Additional information on publications by Martin Nyffeler

In this paper, we present an update on our knowledge on egg predation (oophagy) by spiders. Based on a survey of 233 reports, ghost spiders (Anyphaenidae), lynx spiders (Oxyopidae), jumping spiders (Salticidae), and yellow sac spiders (Cheiracanthiidae) were the most prominent groups of spiders engaged in oophagy. Around 75% of the reports referred to the consumption of lepidopteran and spider eggs worldwide. Another 10% referred to the consumption of eggs/embryos of anurans – especially predation upon embryos of glass frogs (Centrolenidae) by spiders from the families Anyphaenidae and Trechaleidae in the Neotropics. The remaining 17% included rare instances of feeding on eggs of coleopterans, dermapterans, dipterans, heteropterans, homopterans, hymenopterans, acarids, neuropterans, opilionids, and squamates. Our study demonstrates that oophagy in spiders is much more widespread than previously thought, both geographically and taxonomically. The finding that spiders feed on eggs/embryos from so many different invertebrate and vertebrate taxa is novel.

Keywords: Anyphaenidae - Cheiracanthiidae - Oxyopidae - Salticidae - egg predation - Invertebrata - Anura - Squamata

In this paper, 319 incidents of snake predation by spiders are reported based on a comprehensive global literature and social media survey. Snake-catching spiders have been documented from all continents except Antarctica. Snake predation by spiders has been most frequently documented in USA (51% of all incidents) and Australia (29%). The captured snakes are predominantly small-sized with an average body length of 25.9 6 1.3 cm (median 1?4 27 cm; range: 5.8–100 cm). Altogether .90 snake species from seven families have been documented to be captured by .40 spider species from 11 families. About 60% of the reported incidents were attributable to theridiids (’0.6–1.1 cm body length), a spider family that uses strong tangle webs for prey capture. Especially the Australian redback spider (Latrodectus hasselti Thorell, 1870), the African button spider (Latrodectus indistinctus O. Pickard-Cambridge, 1904), an Israeli widow spider (Latrodectus revivensis Shulov, 1948), and four species of North American widow spiders (Latrodectus geometricus C.L. Koch, 1841, Latrodectus hesperus Chamberlin & Ivie, 1935, Latrodectus mactans (Fabricius, 1775), and Latrodectus variolus Walckenaer, 1837) – equipped with a very potent vertebrate-specific toxin (a- latrotoxin) – have proven to be expert snake catchers. The use of vertebrates as a supplementary food source by spiders represents an opportunity to enlarge their food base, resulting in enhanced survival capability. Interestingly, the snakes captured by spiders also encompasses some species from the families Elapidae and Viperidae known to be highly toxic to humans and other vertebrates. Not only do spiders sometimes capture and kill snakes, quite often the tables are turned – that is, a larger number of arthropod-eating snake species (in particular nonvenomous species in the family Colubridae) include spiders in their diets.

Keywords: Araneae - Serpentes - black widow - Latrodectus - Theraphosidae - predation - intraguild predation - venomous spiders - venomous snakes

In this paper 374 incidents of frog predation by spiders are reported based on a comprehensive global literature and social media survey. Frog-catching spiders have been documented from all continents except for Antarctica (>80% of the incidents occurring in the warmer areas between latitude 30° N and 30° S). Frog predation by spiders has been most frequently documented in the Neotropics, with particular concentration in the Central American and Amazon rain forests and the Brazilian Atlantic forest. The captured frogs are predominantly small-sized with an average body length of 2.76 ± 0.13 cm (usually ≈0.2–3.8 g body mass). All stages (eggs/embryos, hatchlings, tadpoles, emerging metamorphs, immature post-metamorphs, adults) of the frogs’ life cycle are vulnerable to spider predation. The majority (85%) of the 374 reported incidents of frog predation were attributable to web-less hunting spiders (in particular from the superfamilies Ctenoidea and Lycosoidea) which kill frogs by injection of powerful neurotoxins. The frog-catching spiders are predominantly nocturnal with an average body length of 2.24 ± 0.12 cm (usually ≈0.1–2.7 g body mass). Altogether >200 frog species from 32 families (including several species of bitter tasting dart-poison frogs) have been documented to be hunted by >100 spider species from 22 families. Our finding that such a high diversity of spider taxa is utilizing such a high variety of frog taxa as prey is novel. The utilization of frogs as supplementary food increases the spiders’ food supply (i.e., large diet breadth), and this is presumed to enhance their chance of survival. Studies from Australia and South America indicate that frogs might be a substantial component in the diet of some mygalomorph spiders (i.e., families Atracidae, Idiopidae, and Theraphosidae). Many more quantitative investigations on the natural diets of tropical spiders are needed before reliable conclusions on the importance of frogs as spider food can be drawn.

Keywords: Araneae - Anura - predation - dart-poison frogs - nutritional importance - survival capability

In this paper, we present an estimate of the predation impact of the global population of insectivorous birds based on 103 (for the most part) published studies of prey consumption (kg ha^-1 season^-1) of insectivorous birds in seven biome types. By extrapolation—taking into account the global land cover of the various biomes—an estimate of the annual prey consumption of the world’s insectivorous birds was obtained. We estimate the prey biomass consumed by the world’s insectivorous birds to be somewhere between 400 and 500 million metric tons year^-1, but most likely at the lower end of this range (corresponding to an energy consumption of ≈ 2.7 × 10¹⁸ J year^-1 or ≈ 0.15% of the global terrestrial net primary production). Birds in forests account for > 70% of the global annual prey consumption of insectivorous birds (≥ 300 million tons year^-1), whereas birds in other biomes (savannas and grasslands, croplands, deserts, and Arctic tundra) are less significant contributors (≥ 100 million tons year^-1). Especially during the breeding season, when adult birds feed their nestlings protein-rich prey, large numbers of herbivorous insects (i.e., primarily in the orders Coleoptera, Diptera, Hemiptera, Hymenoptera, Lepidoptera, and Orthoptera) supplemented by spiders are captured. The estimates presented in this paper emphasize the ecological and economic importance of insectivorous birds in suppressing potentially harmful insect pests on a global scale—especially in forested areas.

Keywords: arthropods - avifauna - breeding season - global impact - insect pests - predation

Spiders have been suspected to be one of the most important groups of natural enemies of insects worldwide. To document the impact of the global spider community as insect predators, we present estimates of the biomass of annually killed insect prey. Our estimates assessed with two different methods suggest that the annual prey kill of the global spider community is in the range of 400–800 million metric tons (fresh weight), with insects and collembolans composing >90% of the captured prey. This equals approximately 1‰ of the global terrestrial net primary production. Spiders associated with forests and grasslands account for >95% of the annual prey kill of the global spider community, whereas spiders in other habitats are rather insignificant contributors over a full year. The spider communities associated with annual crops contribute less than 2% to the global annual prey kill. This, however, can be partly explained by the fact that annual crop fields are “disturbed habitats” with a low buildup of spider biomass and that agrobiont spiders often only kill prey over short time periods in a year. Our estimates are supported by the published results of exclusion experiments, showing that the number of herbivorous/detritivorous insects and collembolans increased significantly after spider removal from experimental plots. The presented estimates of the global annual prey kill and the relative contribution of spider predation in different biomes improve the general understanding of spider ecology and provide a first assessment of the global impact of this very important predator group.

Keywords: Araneae - Collembola - insects - global impact - predation

The salticid spider Phidippus regius C.L. Koch, 1846 is documented preying on small frogs (Hyla spp., Osteopilus septentrionalis) and lizards (Anolis carolinensis and Anolis sagrei) in Florida, USA. Female as well as male P. regius were engaged in feeding on this type of vertebrate prey. A total of eight incidents of P. regius devouring vertebrates have been witnessed in seven Florida counties. Furthermore, we report an incident of a large unidentified Phidippus sp. (possibly P. bidentatus F. O. Pickard-Cambridge, 1901) preying on an immature anole lizard in Costa Rica. P. regius, otherwise known to feed almost exclusively on insects and spiders, is one of the world’s largest salticid spiders reaching a maximum recorded body length of 2.2 cm. Most other salticid spiders appear to be too small in body size to overcome vertebrate prey. Vertebrate predation by salticid spiders has not been previously documented in the scientific literature. Together with Salticidae, spiders from 27 of 114 families (24%) are currently known to occasionally consume vertebrate prey.

Keywords: generalist predators - predation - prey - Dactyloidae - Hylidae - Southeastern USA

Jumping spiders (Salticidae), a group of predominantly insectivorous predators, occasionally supplement their insect prey by deriving nutrients from plant food (‘facultative phytophagy’). The aim of this paper is to give a brief overview of the plant eating activities of salticids based on the published literature. Plant-eating by salticids has been reported from all continents except Antarctica and Europe. With regard to Antarctica it must be said that salticid spiders are absent from there. The previous lack of observations from Europe, on the other hand, may be explained by the fact that plant-eating by salticids is typically found in the warmer areas of the globe (_ 40° latitude) and because most of Europe is located in colder climates (> 40° latitude), it comes as no big surprise that this type of feeding has not yet been detected in European salticids. In order to exploit plant food resources, salticid spiders have to overcome various hurdles. Firstly, plant products such as floral nectar and pollen, serving to attract pollinators, might be chemically protected to deter nectar robbers and pollen thieves. Defensive chemicals such as alkaloids and cardenolides, if ingested along with plant food, may alter the spiders’ behavior as has been demonstrated in laboratory experiments with non-salticid spiders. Whether such behavior-altering chemicals have also an effect on free-living salticid spiders, remains to be researched. Secondly, plant-derived foods such as extrafloral nectar, Beltian bodies or coccid honeydew are aggressively defended by ant bodyguards and spiders must break through the ant defenses in order to get access to these types of food. Salticids detect ants by sight and are able to actively avoid them in most cases. Another situation does occur when the approaching salticid is an ant-mimic perceived by ants as ant (e.g., genus Myrmarachne or Peckhamia); ant-mimicking salticids appear to have unhindered access to plant-derived foods such as extrafloral nectar or coccid honeydew. Thirdly, spiders (adapted to eat insect prey) might require some specific enzymes enabling them to chemically break down plant materials. Currently it seems to be well understood how spiders accomplish the digestion of liquid plant food, whereas the process of digesting solid plant tissue is not yet completely investigated. As in other predaceous arthropods, the ability of spiders to derive nutrients from plant materials is broadening these animals’ diet which may have survival value during periods of prey scarcity.

Keywords: ant bodyguards - ant-mimics - defensive chemicals - facultative phytophagy - geographic distribution - plant food - Salticidae

In this paper more than 50 incidences of bats being captured by spiders are reviewed. Bat-catching spiders have been reported from virtually every continent with the exception of Antarctica (≈90% of the incidences occurring in the warmer areas of the globe between latitude 30° N and 30° S). Most reports refer to the Neotropics (42% of observed incidences), Asia (28.8%), and Australia-Papua New Guinea (13.5%). Bat-catching spiders belong to the mygalomorph family Theraphosidae and the araneomorph families Nephilidae, Araneidae, and Sparassidae. In addition to this, an attack attempt by a large araneomorph hunting spider of the family Pisauridae on an immature bat was witnessed. Eighty-eight percent of the reported incidences of bat catches were attributable to web-building spiders and 12% to hunting spiders. Large tropical orb-weavers of the genera Nephila and Eriophora in particular have been observed catching bats in their huge, strong orb- webs (of up to 1.5 m diameter). The majority of identifiable captured bats were small aerial insectivorous bats, belonging to the families Vespertilionidae (64%) and Emballonuridae (22%) and usually being among the most common bat species in their respective geographic area. While in some instances bats entangled in spider webs may have died of exhaustion, starvation, dehydration, and/or hyperthermia (i.e., non-predation death), there were numerous other instances where spiders were seen actively attacking, killing, and eating the captured bats (i.e., predation). This evidence suggests that spider predation on flying vertebrates is more widespread than previously assumed.

Current knowledge of spiders in agroecosystems (excluding tree crops) reported in European and US literature is discussed comparatively, in an attempt to relate spider community structure to pest control potential.
The spider fauna of agroecosystems in the northern-temperate zone of Europe is strongly dominated by small linyphiid spiders that capture tiny insects in their sheet webs, including large numbers of pest aphids. In the US, spider guild structure is more complex, and hunters (especially, Oxyopidae, Salticidae, Clubionidae, Thomisidae, and Lycosidae), that have broader diets (including lepidopteran and heteropteran pests), numerically prevail in many locations. Spider populations increase to high densities (2-600 m²) in European field crops, but densities are typically much lower (0.02-14 m²) in US annual crops. Agroecosystem spiders, in both Europe and the US, feed rather infrequently, but they contribute to pest control as part of larger assemblages of natural enemies, and there is potential for increasing their density and impact in both continents.
Many of the differences between continents in spider guild structure, density and feeding patterns highlighted in this paper are likely to be attributable to climatic differences. Most of the US data originate from more southern latitudes (i.e., subtropical and Mediterranean climates) with distinctly higher mean annual temperatures compared to the European study areas, which are in the northern-temperate zone. Spider communities may respond to climate directly, and also indirectly via food availability and antagonists. In addition, differences in crop structure and cultural practices (including habitat diversification and the provision of ground cover) could influence spider density and community organisation. Mean farm size is an order of magnitude less in Europe than in the US and this is likely to be associated with greater habitat diversity, which is known to increase spider abundance.
Currently, there is a dearth of field studies from southern Europe (Mediterranean climate) and the northern regions of the US (humid continental climate). The few data available from such regions indicate that the patterns of spider predation may differ less between the two continents if sufficient study areas with similar climatic conditions could be compared. The conclusions in terms of biological control are, however, widely applicable, because a large proportion of the productive agricultural land area of Europe is located in more northern latitudes and the reverse is true in the US.

Keywords: review - agroecosystem - biological control - ecology - Araneae - Linyphiidae - North America - biodiversity - distribution - abundance - diets - prey - latitude - temperature

A house spider (Tegenaria atrica C.L. Koch 1843, Agelenidae) was observed, filmed and photographed while feeding on an earthworm. An extensive search in the literature revealed that several arachnologists had noted spiders feeding on earthworms, altogether in 11 different families. Earthworm-eating spiders belong mostly to larger sized species dwelling near the ground in woodlands and grasslands. Since earthworms have a high protein content, they could be a welcome supplement to the spider's usual insect diet.

It has been stated in some literature reports that in the highly cannibalistic wolf spiders (Lycosidae) the adult females do not feed while engaged in maternal care (i.e. their predatory behaviour is inhibited), whereas other reports based on laboratory studies indicate that maternal females resume feeding. During a two-year field study on the feeding habits of the wolf spiders Pardosa agrestis, P. palustris and P. amentata, I had the opportunity to investigate the question whether in these species maternal females do feed (or not). Overall, 25 instances of wolf spider mothers feeding during the period of maternal care are reported. Eighteen cases refer to egg sac-carrying females, 7 cases to pulli-carrying females. It must be stated, however, that the feeding rate of maternal females was significantly lower than that of non-maternal females, which is in agreement with the findings of other researchers obtained in the laboratory. It is hypothesised that there may be genusspecific behavioural differences between free-moving and burrowing wolf spider species which may (at least in part) explain the apparent discrepancies between the reports of various authors.

In this article, an overview of the general feeding patterns of common agroecosystem spiders is presented. Five groups of web-weavers (Tetragnathidae, Araneidae, Theridiidae, Linyphiidae, Dictynidae) and five groups of hunters (small-sized Oxyopidae, large-sized Oxyopidae, Thomisidae, Salticidae, Lycosidae) are analyzed comparatively (based on 40 prey analyses previously published by various European and US authors). Fewer than 10 insect orders, as well as the order Araneae, make up the bulk of the prey of these spiders. Web-weavers and hunters both basically feed on the same prey orders, but in different proportions. The observed differences reflect in part the very diverse range of life styles and foraging modes exhibited by the various spider groups and, to some extent, differences in prey availability. Web-weavers are almost strictly insectivorous (insects constituting >99% of total prey). Hunters, however, exhibit a mixed strategy of insectivorous and araneophagic foraging patterns (insects constituting 75-90% of total prey). Diet breadth computed with the Inverted Simpson Index was, on average, significantly higher in the hunting spiders than the web spiders. There seems to be a consistent trend of greater diet breadth of the hunters compared to the web-weavers in agroecosystems. Overall, spider individuals of small size (including large percentages of immatures) numerically dominate the faunas of field crops, and these feed primarily on tiny prey (<4 mm in length).

The ecological impact of spider predation on cotton insects in cotton fields in Texas was investigated. In particular, it was assessed how frequently the spiders feed on four 'key pests' of Texas cotton (i.e., cotton fleahopper Pseudatomoscelis seriatus [Heteroptera: Miridae], boll weevil Anthonomus grandis grandis [Coleoptera: Curculionidae], bollworm Helicoverpa zea [=Heliothis zeal] [Lepidoptera: Noctuidae], and tobacco budworm Heliothis virescens [Lepidoptera: Noctuidae]) and to what extent this may impact the mortality of these pests. The data were collected over a period of totally ≈ 200 h of visual observations in the course of two field projects: The first project was conducted during the summer of 1985 in an unsprayed (6.5 ha) cotton plantation near Austonio, Houston County, East Texas. The second project was undertaken during the summer of 1988 in an unsprayed (13.6 ha) cotton plantation located near Snook, Burleson County, Central Texas, approximately 100 km southwest of the previous study site.
The spider assemblages found in cotton in Austonio and Snook were quite similar and represent a species complex typical for extensive cotton growing areas throughout the U.S. cotton belt, with lynx spiders (Oxyopidae) numerically predominating. Lynx spiders consistently constituted > 50% of the spider total throughout the growing season. The second most abundant spider group, the orb-weavers (Araneidae and Tetragnathidae), constituted ≈ 10% of the spider total. Two species of lynx spiders occur in these fields: the 'striped lynx' Oxyopes salticus and the 'green lynx' Peucetia viridans. The numerically dominant Oxyopes occurred in average densities of ≈ 1-1.5/m² during mid-season in both plantations. [Peucetia is less frequently found in cotton and is therefore expected to be of minor importance as a potential natural enemy of pests in the cotton fields. ] The studies focussed primarily on the numerically dominant lynx spiders and orb-weavers.
To evaluate the predatory significance of the lynx spiders relative to the other predaceous arthropods occurring in cotton, the total number of predation events observed attributable to lynx spiders versus other arthropod predators was compared based on the data which had been collected in Snook. A total of 134 arthropod predators with prey in their chelicerae/mandibulae were monitored during the 108 h observation period, which included 94 lynx spiders versus 40 other predators. Thus, 70% of all predation events observed were attributable to lynx spiders which indicates that these spiders were the dominant predators in this cotton plantation. Similar patterns of a predominance of lynx spider predation were observed in Austonio, too.
The predation rate (: no. prey killed/spider/day) was estimated with a visual method based on average feeding frequency (percentage spiders with prey in their chelicerae) observed in the field, average handling time, and hunting (searching) time; it was estimated that a subadult/adult Oxyopes (representing a typical agroecosystem spider) may capture ≈ 1 prey organism on an average rainfree day in the field (during the middle of the growing season). The same spiders feed at several times higher rates in laboratory feeding experiments if food is offered ad libitum (as is known from literature), which suggests that in the field these spiders often feed below their maximum feeding capacity. Thus, the spiders can be expected to increase their predation rate during severe outbreaks of insect pests (i.e., 'functional response').
The majority of the lynx spiders in cotton were of small size (i.e., Oxyopes). Oxyopes captures a wide variety of small-sized arthropods ranging from 0.6 to 6 mm length ( ≈ 2.5 mm optimal prey length). [ In contrast to this, the larger Peucetia feeds over a broader range of prey size classes and consequently captures a higher proportion of the larger prey organisms, but because this species is much less abundant than Oxyopes, its contribution to the overall predation impact is rather low. ] Likewise, most orb-weavers occurring in cotton were of small body size. Overall, spider individuals of small size (including large percentages of immatures) numerically dominate the faunas of the investigated cotton fields, and these spiders feed primarily on tiny prey organisms (≤ 3 mm in length).
With a body length range of 1.1-2.9 mm (third instar to adult) cotton fleahoppers ideally fit the optimal prey length of ≈ 2.5 mm for Oxyopes. [ Peucetia, that captures on the average significantly larger-sized prey than Oxyopes, seems to be less efficient in capturing fleahoppers.] Oxyopes shows considerable flexibility in switching its feeding patterns in response to prey availability. - In the cotton plantation in Austonio, the numbers of cotton fleahoppers were below the economic threshold, and consequently very low predation rates on fleahopper prey by spiders were observed (0% fleahoppers in the diet of Oxyopes); instead, Oxyopes fed heavily on red imported fire ants (22% of the diet) and other nonfleahopper prey. - A totally different scenario was observed in the cotton plantation in Snook, where cotton fleahoppers occurred in fairly high numbers; in this situation, Oxyopes fed heavily on these pests (fleahoppers constituting 24% of the diet). - These data indicate that Oxyopes may feed heavily on other predators such as fire ants when pests are rare; however, when pests become abundant this spider can largely switch to pestiferous species such as fleahoppers as a major food source.
The assessment of the killing power of Oxyopes, based on the predation rate and the predator-to-prey ratio (i.e., number of Oxyopes individuals per fleahopper), suggests that this spider contributes significantly to mortality of the cotton fleahopper (≥ 15% prey mortality per day, in the middle of the growing season) in the plantation in Snook; additional fleahopper mortality is attributable to other spiders and predaceous insects, though they are less effective than Oxyopes. - The other key pests (i.e., boll weevil, bollworm, and tobacco budworm) were poorly represented in the spider diets, which apparently reflects that these pests occurred in numbers far below economic injury levels (it is assumed that fire ants are the cause of the low pest levels). - The contribution of the spiders to fleahopper mortality, however, varies between the different fields and within different years, due to the spatial and temporal fluctuations of the numbers of spiders and fleahoppers. An approximately 30 times higher frequency of predation on fleahoppers was recorded in Snook compared to Austonio. Consequently the economic benefit due to these predators varies in different situations.
Based on population density counts in the cotton plantation in Austonio and the assessment of the predation rate, it was estimated that lynx spiders killed perhaps ≈ 0.6% of the potential prey per day in the middle of the growing season; it is assumed in the literature that mortality rates of that magnitude already have a significant positive impact on the community stability; thus, spiders can be considered to serve as 'stabilizing agents' (compare Turnbull, 1973, "Ecology of the true spiders", in: Annu. Rev. Entomol. 18, 305-348).

Although the beneficial status of the spiders as insectivores has been widely recognized for quite some time, biologists by and large seem to be rather unfamiliar with the specific feeding habits of this very diverse order. We present an overview of the feeding patterns of 10 groups of common agroecosystem spiders to inform entomologists and ecologists concerned with issues of natural biological control. The various spider groups discussed in this article exhibit a very diverse range of life styles and foraging modes, which is reflected in the diversity of their feeding patterns. Implications of the insectivorous activities of these predators for natural pest control are discussed.

Keywords: spiders - predation - diets

Spiders aid in the control of cotton pest insects by direct predation and through incidental mortality (e. g., aphids adhering to a spider web and suffering mortality without spider intervention). Some spider species can be key predators (causing irreplaceable mortality to a pest species) of key insect pests such as the cotton fleahopper, Pseudatomoscelis seriatus (Reuter), a prey type for which spiders provide probably the most effective natural control. Most spider species serve as members of vast predator assemblages within cotton ecosystems, helping to restrict major and minor pests to low densities. Evidence suggests that arrays of spider species may act as ecological indicators of the degree to which pest insects are under control in cottonfields. Spider species have been observed feeding upon every major and most minor, secondary, or occasional insect pests of Texas cotton.
The discussion presented in this bulletin of pest categories and of appropriate corresponding biological control agents can help to unify the biological control concept for cotton and other agricultural crops. The three pest groups discussed consist of sessile external (SE) arthropod pests; sessile internal (SI) arthropod pests; and mobile, visually acute (MV) arthropod pests. Although spider predation influences all the groups to some degree, it is most effective against the MV category of pests.
A key and illustrations to all known species of spiders found on Texas cotton is provided to help in species identification. The known biology and predation ecology of each spider species found on Texas cotton is discussed both from the field experiences of the authors and from the literature.

Keywords: spiders - Araneae - taxonomy - biocontrol agent - cotton - Texas - identification key - predation ecology

Spiders inhabiting the soil surface of a winter wheat field were examined using pitfall traps near Zurich, central Europe. The soil surface spider community was dominated by two species of wolf Spiders Pardosa agrestis (WESTRING) and Pardosa palustris (L.) (Lycosidae) and three species of sheet-web weavers Erigone atra (BLACKWALL), Erigone dentipalpis (WIDER) and Oedothorax apicatus (BLACKWALL) (Linyphiidae). The identity and average number of spiders collected in the traps over time between field border and center were compared revealing that the number of wolf spiders on the border did not differ significantly from the center. However, the sheet-web weavers expressed a consistent trend of slightly greater numbers in the field's center compared to the border. Computation of the dispersion index (after MORISITA) indicates aggregated patterns throughout the field for both Lycosidae and Linyphiidae caught in the pitfall traps. The combined number of spider individuals showed an overall increase as the season progressed. Over 12000 spiders were collected from the 2 ha winter wheat field by means of 45 (7 cm diam.) pitfall traps in less than 3 months, whereby this high number is providing additional evidence for previous work reported in the literature of winter wheat field colonization by large numbers of spiders. The capacity of soil surface spiders to build up these high numbers, potentially consuming field crop insect pests at elevated rates suggests that they may play a significant role as natural control agents. The effectiveness of these spiders as natural enemies may be limited only by their apparently low feeding frequency reflecting a low rate of metabolism.

Spider predators were studied on flowering lemon horsemint, Monarda citriodora Cervantes, Lamiaceae, at two Texas locations to assess their potential as agroecosystem colonizers and natural control agents of insect pests. Oxyopes salticus Hentz, Peucetia viridans (Hentz), Misumenops celer (Hentz), and Metaphidippus galathea (Walckenaer) were predominant and are known (1) to disperse via air currents (ballooning), (2) to colonize cotton fields, and (3) to forage on cotton insect pests. About 90% of the spider individuals found on horsemint plants represent species known to attack and kill cotton fleahoppers, Pseudatomoscelis seriatus (Reuter), a key pest of cotton.

Keywords: horsemint - wild plants - spiders - predators - cotton fleahopper - Texas

The efficacy of predators of immature cotton fleahoppers, Pseudatomoscelis seriatus (Reuter), was calculated using field and laboratory cage confinement tests for consumption rate. The predators tested were the striped lynx spider, Oxyopes salticus Hentz; the black and white jumping spider, Phidippus audax (Hentz); the celer crab spider, Misumenops celer Hentz; and the red imported fire ant, Solenopsis invicta Buren. The spider predators were evaluated in a cotton field using predator-prey confinement cages on cotton plants. Average percent control (sensu Abbott, 1925) of fleahoppers by O. salticus, P. audax, and M. celer were 42 %, 66 % and 32 % respectively. The rate of fleahopper consumption by red imported fire ants was measured in the laboratory using various numbers of ants and fleahoppers. Daily percent control by ants ranged from 0.5 % (single ant and fleahopper) to 100 % (colony linked). The functional response of the 4 arthropod species to different prey numbers is illustrated and discussed as is the relative potential usefulness of natural enemies to suppress fleahoppers on cotton.

Keywords: Pseudatomoscelis seriatus - predation - Miridae - cotton - natural control

Examples of spiders preying upon the eggs of Araneae and Insecta are given from descriptions found in the literature from different regions of the world. In many cases, spiderlings or female spiders were feeding on the eggs of conspecifics (cannibalism). Evidence of conspecific predation on eggs has been reported for the families Dipluridae, Uloboridae, Scytodidae, Loxoscelidae, Pholcidae, Theridiidae, Agelenidae, Lycosidae, Gnaphosidae, Clubionidae, Thomisidae and Salticidae. Spiders feeding on the eggs of other species (interspecific predation by Salticidae upon eggs of other Salticidae and Uloboridae; Theridiidae upon the eggs of orb-weaving spiders) has also been noted. Evidence of spiders as predators of insect eggs is reported from North and South America, and Australia, largely in agroecosystems and forest ecosystems. In most cases, the spiders were observed feeding on the eggs of Lepidoptera (families Noctuidae, Tortricidae, Lymantriidae, Pyralidae and Sphingidae), and to a lesser extent, on coleopteran eggs (family Curculionidae).

Predation by the jumping spider, Plexippus paykulli (Audouin), was recorded in a synanthropic habitat in Texas. Prey ranged in size from 3.4 to 19mm (x̅ ± SE = 6.79 ± 0.96mm) and consisted almost entirely of the German cockroach, Blatella germanica (L.) (96%, N=28). When compared to 9 other species of cursorial hunting spiders using Levins'niche breadth formula, the value for P. paykulli was 3 times lower than the value for the species with the narrowest prey diversity, to 53 times lower than the species with the broadest, indicating a trend toward monophagy. However, P. paykulli is known as a highly polyphagous predator with a broad feeding niche and the low dietary diversity observed is probably facultative monophagy, a feeding strategy invoked by a plethora of a single prey species accompanied by scarcity of alternative prey within the habitat. The ability of jumping spiders to narrow down their feeding niche during periods of an abundance of a single prey species and simultaneous rarity of other prey is significant from the standpoint of natural control, both in urban and agricultural settings.

In an unsprayed cotton field in east Texas, orb weavers were one of the numerically dominant groups of spiders, constituting 10% of all spiders collected by D-vac during the summer of 1985 (range, 0.04 individuals/m² in June to 0.72 individuals/m² in August). Direct counts, conducted during peak orb-weaver density in August, showed that 0.86 individuals/m² were found. Their prey consisted of insects (> 99%) and spiders (< 1%). Aphids, which occasionally reach pest status in Texas cotton, were the most abundant prey of all five spiders (34.6-90%). Other important prey included small dipterans, cicadellids, and hymenopterans. Differences among the five spider species indicate that prey selection was occurring; this seems to be determined by web location, web inclination, and web strength.

Keywords: Arachnida - orb-weaving spiders - cotton - predation

Predation by wolf spiders (Pardosa spp.) was studied for two years in two winter wheat fields in eastern Switzerland, one field being investigated each year. The following wolf spiders predominated in the investigated wheat fields: Pardosa agrestis (Westr.), Pardosa amentata (Clerck), and Pardosa palustris (L.). P. agrestis constituted greater than or equal to 75% of all Pardosa spp. observed in the field. Diptera, Collembola, and aphids constituted the major components in the spiders' diet (combined ca. 80% of the identified prey by numbers).

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In winter wheat fields of eastern Switzerland, the foraging of the comb-footed spider Achaearanea riparia (Blackw.) was studied. This spider - occurring in the winter wheat ecosystem in estimated numbers of ca. 0.6 ind./m² - was observed to be a generalist predator of small to medium-sized arthropods. With its irregular webs - which A. riparia spins in the lowest 15% of the foliage - this spider captured a variety of arthropods, primarily of the orders Hymenoptera (36% by numbers, mostly apterous ants), Coleoptera (19%, mostly Staphylinidae, and Carabidae of the genus Amara), Homoptera (14%, mostly aphids), Diptera (6%), and Araneae and Acari (6%, Micryphantidae and Oribatidae).

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Diets of the four small-sized web-building spiders Dictyna segregata Gertsch and Mulaik, Theridion australe Banks, Tidarren haemorrhoidale (Bertkau), and Frontinella pyramitela (Walckenaer) were studied in an unsprayed cotton agroecosystem in eastern Texas by analyzing prey found in these spiders' webs. Aphids were the most dominant food category in the potential prey complex (D-Vac samples) as well as in the actual prey (insects found in webs) of the four spider species. Since these spiders captured mainly small insects with a size of <3mm, they can be considered to be potential predators of the cotton fleahopper.

In a dry grassland (Bromus meadow) located in the protected "Katzensee" area (eastern Switzerland) the composition of foliage-dwelling spiders was studied by taking sweep net samples during one summer season. The total number of immature plus adult spiders per 100 single sweeps increased (quadrupled) from June to August (egg-laying of many adults in spring followed by hatching of the spiderlings in summer). A yearly total of 234 adult specimens - composing > 2/3 females and representing 21 identified species - was collected by sweeping (based on more than 3000 single sweeps). Immature stages (overall, 82%) outnumbered the adult spiders in the sweep net samples. Thirteen spider families were found in the dry meadow. The seven families Thomisidae, Salticidae, Micryphantidae, Tetragnathidae, Pisauridae, Theridiidae, and Araneidae prevailed in the yearly total of collected spiders (combined 89% of the 1295 immature plus adult specimens, 96% of the adults). Six species - Enoplognatha ovata (Clerck), Evarcha arcuata (Clerck), Heliophanus flavipes (Hahn), Hylyphantes nigritas (Simon), Tetragnatha pinicola L. Koch, and Xysticus cristatus (Clerck) - combined made up > 80% of all collected adult spiders. The non-webbuilding spiders E. arcuata and X. cristatus considered to be insectivorous generalist predators were the two most frequently collected species. The results are compared with data of the foliage-dwelling spider community of another grassland habitat located in the same geographic area.

Twenty females of the orb-weaving spider Argiope aurantia Lucas were introduced into a cotton field in east Texas in order to study the feeding ecology of this spider. In the 24 h after the release of these spiders in the cotton field, one had moved over a distance of 53 m. The released spiders spun webs with an average diameter of 33.5 cm with the hub an average of 39 cm above the ground. The diet of A. aurantia was diverse which characterizes this species as a food generalist. Major food components were aphids (30 %), Diptera (26.8 %), grasshoppers (17.9 %), and Hymenoptera (12.6 %). The spiders' prey length ranged from 0.4 to 47 mm (mean = 7.7 ± 0.83 mm). Adult females of A. aurantia have the potential to kill prey of up to ca. 200 % of their own size. However, two-thirds of the prey items had a length of < 3 mm, while only 25 % of the prey items had a length of ≥ 20 mm. A. aurantia was found to be a predator of the cotton fleahopper (about 1 % of the spiders' diet), which is a key pest of cotton.

Keywords: Spiders - cotton - Argiope - orb-weavers - prey size

Predation by green lynx spider, Peucetia viridans (Hentz), was studied on cotton and woolly croton plants in East Texas. This species feeds both diurnally and nocturnally. P. viridans was observed feeding on insects of orders Diptera, Hymenoptera, Heteroptera, Homoptera, Coleoptera, Lepidoptera, Neuroptera, and Odonata, as well as on several spider species. Predaceous arthropods (e.g., Hippodarnia conuergens Guérin-Méneville, Coccinellidae; Chrysoperla rufiIabris [Burmeister], Chrysopidae) constituted more than half of the spiders' diet. In cotton, P. viridans was found to be a predator of the pests Heliothis zea (Boddie) and Alabama argillacea (Hübner) (together 8% of the spiders' prey). Size of killed prey in cotton ranged between 0.14- and 1.3-fold the spiders' size (average prey length, 5.90 ± 0.99 mm). On woolly croton plants, P. viridans was often seen feeding on cotton fleahopper, Pseudatomoscelis seriatus (Reuter) (numerically almost 30% of the spiders' prey), which is a key pest in cotton. It was estimated that on cotton and croton plants in East Texas, one P. viridans captured an average of less than one prey daily. Our results are compared with data in the literature on the diet of P. viridans.

Keywords: Peucetia - Pseudatomoscelis - cotton - croton - predation - diet

The foliage-dwelling spiders of an abandoned grassland ecosystem (Valeriano-Filipenduletum, Carex acutiformis Ehrh. type) in eastern Switzerland were studied from June to September by the sweeping technique. A total of 632 adult specimens representing 22 identified species had been collected by sweeping (based on totally ca. 2000 single sweeps). More than two thirds of the sampled adult spiders were females. At all times, more immature than adult spiders were captured (overall, 83% immatures). Among the 3756 collected spiders (immatures plus adults), the six families Agelenidae, Araneidae, Micryphantidae, Pisauridae, Salticidae, and Tetragnathidae prevailed in the sweep net samples (combined ca. 90% of all spiders). The five species Evarcha arcuata (Clerck), Hylyphantes nigritus (Simon), Neottiura bimaculata (L.), Pisaura mirabilis (Clerck), and Tetragnatha extensa (L.) constituted combined > 80% of all adult spiders sampled by sweeping. The web-building spiders T. extensa and H. nigritus were the two species most frequently captured. Adults of large orb-weaving spiders (Argiope bruennichi [Scopoli], Araneus quadratus Clerck, and Araneus diadematus Clerck) were abundant in the investigated grassland habitat (assessed by web counts), but obviously underproportionately represented in the sweep net samples. Considering the total number of spiders (immatures plus adults) per 100 single sweeps, a strong increase from spring to late summer was noticed which is considered to be primarily due to egg-laying of the most dominant species in spring followed by hatching of the spiderlings in the course of the summer. Since spiders are abundant predators in this grassland ecosystem (ca. 0.1 m² web area/m² ground area, alone due to orb-weavers in August/Sept.), they may be important mortality agents of grassland arthropods.

Prey records of the orb-weaving spider Cyclosa turbinata (Walckenaer) and the wolf spider Lycosa rabida Walckenaer in an east Texas agroecosysten are presented. Aphids were numerically the most dominant component in the potential prey (based on D-Vac samples) as well as in the actual prey found in webs of C. turbinata. L. rabida was studied during the night using the head-light method (gleaming eyes) and ca. 4% of those collected where feeding. It is estimated that L. rabida captured less than one prey per spider daily.

In a spruce forest near Aarau (Switzerland) a small erigonid spider, Troxochrus nasutus Schenkel, was observed feeding on Hylurgops palliatus Gyll. and Pityogenes chalcographus L. bark beetles.

A note on spiders killing bark beetles - In a spruce forest near Aarau (Switzerland) web-building spiders were observed to be predators of Hylurgops palliatus Gyll. and Pityogenes chalcographus L. bark beetles.

A field study near Zurich (Switzerland) has shown that the orb-weaving spider Argiope bruennichi (Scopoli) has a predatory behaviour towards Lepidoptera which is similar to that of Argiope-species in other continents. Instead of the normal sequence: wrapping up of prey → bite, lepidopterous insects are first bitten and then wrapped up.

The most important literature on the ecological importance of spiders for forest ecosystems was compiled and analyzed. Forest spiders normally live in densities of 50 to 200 individuals/m² and prey, at least in Europe, predominantly on small soft-bodied insects (Diptera and Collembola mainly). However, bigger insects, including various forest pests, are also found in their prey. According to the present stand of knowledge the spiders of the soil surface seem to be important insect predators, whereas the ecological importance of spiders living on the trees is still controversial.

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From 1976-1979, the ecology of spiders was investigated in abandoned grasslands, cultivated meadows and cereal fields near Zurich (Switzerland). The spiders of such ecosystems live in two strata, (1) on the ground surface, (2) in the vegetation zone. Different spider communities are found in the two strata.
In abandoned grasslands, the spiders live undisturbed all year round. They can therefore build up relatively large populations in these biotopes (near Zurich about 10 spiders/m²; significantly higher values are reported in literature). Cultivated fields, on the other hand, are periodically mown, whereby the living space and the egg sacs of many spiders are destroyed. Only relatively small spider populations live therefore in the vegetation zone of cultivated fields (about 1 spider/m² in cultivated meadows and 0.1-0.6 spiders/m² in cereal fields). The ground surface of cultivated fields is rather densely populated (15-42 spiders/m² in cultivated meadows and 10-50 spiders/m² in cereal fields).
The spiders in the vegetation zone of cultivated meadows and cereal fields are primarily predators of Diptera and Homoptera. In the vegetation zone of abandoned grasslands, in addition honey bees and/or grasshoppers can form an essential part of the prey biomass of large web-building spiders. On the ground surface of cultivated meadows and cereal fields, the predominant spiders are mainly predators of small, soft-bodied insects (Collembola, Diptera, aphids etc.). From the food analyses it follows that the spiders are predators of pest insects (e.g. cereal aphids), indifferent species (most Diptera), and of beneficial arthropods as well (honey bees, Chrysopidae, Coccinellidae etc.).
The energy flow (prey killed) through the spider communities of the vegetation zone of abandoned grasslands can be high, e.g. >900 MJ/ha/year in a megaphorbe meadow. In comparison, the energy flow through the spider communities of cultivated fields is significantly lower, e.g. 1.1-6.5 MJ/ha/year in cereal fields, and <0.5 MJ/ha/year in maize fields. The energy flow through the ground-dwelling spider communities of cultivated fields should amount to about 10-50 MJ/ha/year.
Abandoned grasslands often are veritable spider paradises. In these ecosystems, the spiders of the vegetation zone represent an important predator group. In the vegetation zone of cereal fields, on the contrary, spiders do not seem to play a significant ecological role. Further studies will show, to what extent the ground-dwelling spiders in cultivated meadows and cereal fields are of ecological importance.

The results of studies on the feeding ecology of spiders from 1974-1980 can be summed up as follows: All species of spiders examined fed exclusively on evertebrates (Insecta, Arachnida, Isopoda, Myriapoda, Lumbricidae). In most cases, more than 90 % of the food consisted of insects.
Numerous spiders living in the vegetation stratum feed mainly on small flying insects, such as Diptera and aphids. The same is true for the dominant spiders living on the surface of the soil, though their prey spectrum is supplemented by Collembola and apterous aphids. Thus in the average prey spectrum of spiders small insects with a soft cuticle dominate. Exceptions are found with Argiope bruennichi, a predator of grasshoppers and bees, Agelena spp. feeding mainly on relatively large insects, Xysticus cristatus, which, when hunting on the ground, preys on ants and spiders, Achaearanea riparia, preying on ants and-beetles, Coelotes terrestris, a specialized predator of beetles, and Pholcus phalangioides, preying on wood-lice, spiders, opilionides etc. The prey spectra of the spider species examined vary considerably in breadth. So the food spectrum of the funnel-web spiders of the polyphagous genus Agelena is large compared to that of the oligophagous C. terrestris. Whereas in most spider species the size of their prey is relatively small or only reaches the size of the predator (size of prey ≤ size of predator), some species, mainly of Thomisidae and Theridiidae, prey at times upon prey larger than they are.
Spiders are secondary consumers belonging predominantly to herbivor food chains. Wolf spiders living on forest grounds intervene also in detritus food chains. Scorpionflies (genus Panorpa) often feed on prey animals in spider webs (food robbery).

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In a beech spruce forest near Zurich (Switzerland) studies on the feeding ecology of the wolf spider Pardosa lugubris (Walck.) were carried out. Only 6% of 513 wolf spiders caught by hand held a prey (strongly deformed) between their chelicerae. The food of P. lugubris exclusively was composed of small, soft-bodied arthropods (Insecta, Arachnida). > 85 % of the identified prey animals consisted of Collembola (Genera Orchesella and Tomocerus) and small Diptera

In the vegetation stratum of uncultivated meadows spiders represent a great potential of insectivorous predators. If uncultivated meadows are converted to cultivated land the predator potential of the vegetation is lost to a great part. Contrary to this the epigeous spiders reach relatively high densities also in cultivated land and may therefore stabilize certain insect populations of meadows and cereal fields.

Dead insects caught in spider webs attract diverse carnivorous arthropods (predators and saprophages). Especially juvenile stages of orb-weaving spiders (Nuctenea umbratica, N. cornuta, N. sclopetaria) as well as adult scorpionflies enter the webs of adult spiders and feed there on the dead insects. Since the intruders feed on the potential prey of the web-owners the relationship between the two must be classified as parasitism. However, these intraspecific and interspecific thefts of food are probably special forms of nutritional parasitism with transitions to commensalism. The question how the kleptoparasites avoid being killed by the host spiders has been discussed. Our observations are compared with other published reports and lead to the conclusion that all transitions from purely occasional thefts of food to permanent and compulsory kleptoparasitism exist.

Ecological investigations on spider populations of cereal and rape fields near Zurich (Switzerland) and their prey spectra in 1976/77 led to the conclusion that the population densities of spider populations of the vegetation strata were low (< 0.1-0.1 spiders/m² in corn fields, and 0.1-0.6 spiders/m² in other fields) and their impact on insect populations almost insignificant (100-1200 g insects/ha/year, mostly small diptera and aphids). Due to the destruction of the spider eggs at harvest at the end of July, the fields have to be repopulated from extensively or not cultivated small biotopes such as road sides and the margins of woods etc. every year. The yearly preying activity of the spiders of cereal and rape fields is thus restricted to 60-70 d between immigration and harvest, except for corn fields harvested later in the year. Numerically most dominant in the vegetation of cereal and rape fields were Theridium impressum, Tetragnatha extensa, Mangora acalypha, Araneus cucurbitinus, A. cornutus, and A. ceropegius

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