Spatial and temporal variation in a suite of life-history traits in two species of wolf spider

Abstract.  1. Life-history traits and density were assayed in seven populations of two sympatric species of wolf spider for three consecutive years. The goal of the study was to quantify population dynamics and its relation to spatial and temporal life-history variation.
2. Adult female body size and fecundity varied significantly, among field sites and among years, in both species. Female spiders of both species differed in mean relative reproductive effort among sites, but not among years. The size of offspring was invariable, with no significant differences due to site or year.
3. All populations of both species tended to either decrease or increase in density during a given year and this was tightly correlated with changes in prey consumption rates.
4. Since life-history patterns are determined primarily by selection, it is concluded that size at sexual maturity for females is phenotypically plastic and responds to changes in prey availability. Offspring size however is not plastic and it is likely that other selection forces have determined offspring size. Temporal fluctuations in population size are correlated over a large area relative to dispersal capabilities for these species and conservation efforts for invertebrates must take this into consideration.     

Genetic quality of individuals impacts population dynamics

Ample evidence exists that an increase in the inbreeding level of a population reduces the value of fitness components such as fecundity and survival. It does not follow, however, that these decreases in the components of fitness impact population dynamics in a way that increases extinction risk, because virtually all species produce far more offspring than can actually survive. We analyzed the effects of the genetic quality (mean fitness) of individuals on the population growth rate of seven natural populations in each of two species of wolf spider in the genus Rabidosa , statistically controlling for environmental factors. We show that populations of different sizes, and different inbreeding levels, differ in population dynamics for both species. Differences in population growth rates are especially pronounced during stressful environmental conditions (low food availability) and the stressful environment affects smaller populations (<500 individuals) disproportionately. Thus, even in an invertebrate with an extremely high potential growth rate and strong density-dependent mortality rates, genetic factors contribute directly to population dynamics and, therefore, to extinction risk. This is only the second study to demonstrate an impact of the genetic quality of individual genotypes on population dynamics in a wild population and the first to document strong inbreeding–environment interactions for fitness among populations. Endangered species typically exist at sizes of a few hundred individuals and human activities degrade habitats making them innately more stressful (e.g. global climate change). Therefore, the interaction between genetic factors and environmental stress has important implications for efforts aimed at conserving the Earth's biodiversity.     

Food limitation of population density in the orb-wed spider,Nephila clavata

Field studies were conducted to clarify whether variation in food availability among habitats influences population density, and whether population density has a negative effect on foraging success in the orb-web spider, Nephila clavata. Lifetime food consumption per individual (i.e., foraging success) strongly correlated with mean body size of adult females and mean fecundity in populations. Also, there was a positive correlation between foraging success and population density. Since foraging success reflected potential prey availability in the habitat, food resource appeared to be a limiting factor for populations in this spider. Mean fecundity per individual correlated with population density of the following year, suggesting that decreased reproduction is a major component of food limitation on population density. Consistent defferences in mean body size between particular sites were observed over years, while such difference was less obvious in density. Thus, ranking of food abundance among habitats seems to be predictable between years. A field experiment revealed that an artificial increase in population density had no negative effect on the feeding rate of individuals, suggesting that intraspecific competition for food is not important in this species.     

Guiding lights: Foraging responses of juvenile nocturnal orb‐web spiders to the presence of artificial light at night

The reach of artificial light at night (ALAN) is growing rapidly around the globe, including the increasing use of energy‐efficient LED lights. Many studies document the physiological costs of light at night, but far fewer have focused on the potential benefits for nocturnal insectivores and the likely ecological consequences of shifts in predator–prey relationships. We investigated the effects of ALAN on the foraging behaviour and prey capture success in juvenile Australian garden orb‐web spiders (Eriophora biapicata). Laboratory experiments demonstrated that juvenile spiders were attracted to LED lights when choosing foraging sites, but prey availability was a stronger cue for remaining in a foraging site. Field experiments revealed a significant increase in prey capture rates for webs placed near LED lights. This suggests that any physiological costs of light at night may be offset by the foraging benefits, perhaps partially explaining recently observed increases in the size, fecundity and abundance of some orb‐web spider species in urban environments. Our results highlight the potential long‐term consequences of night lighting in urban ecosystems, through the impact of orb‐web spiders on insect populations.     

Temperature dependency of predation: Increased killing rates and prey mass consumption by predators with warming

Temperature dependency of consumer–resource interactions is fundamentally important for understanding and predicting the responses of food webs to climate change. Previous studies have shown temperature‐driven shifts in herbivore consumption rates and resource preference, but these effects remain poorly understood for predatory arthropods. Here, we investigate how predator killing rates, prey mass consumption, and macronutrient intake respond to increased temperatures using a laboratory and a field reciprocal transplant experiment. Ectothermic predators, wolf spiders (Pardosa sp.), in the lab experiment, were exposed to increased temperatures and different prey macronutrient content (high lipid/low protein and low lipid/high protein) to assess changes in their killing rates and nutritional demands. Additionally, we investigate prey mass and lipid consumption by spiders under contrasting temperatures, along an elevation gradient. We used a field reciprocal transplant experiment between low (420 masl; 26°C) and high (2,100 masl; 15°C) elevations in the Ecuadorian Andes, using wild populations of two common orb‐weaver spider species (Leucauge sp. and Cyclosa sp.) present along the elevation gradient. We found that killing rates of wolf spiders increased with warmer temperatures but were not significantly affected by prey macronutrient content, although spiders consumed significantly more lipids from lipid‐rich prey. The field reciprocal transplant experiment showed no consistent predator responses to changes in temperature along the elevational gradient. Transplanting Cyclosa sp. spiders to low‐ or high‐elevation sites did not affect their prey mass or lipid consumption rate, whereas Leucauge sp. individuals increased prey mass consumption when transplanted from the high to the low warm elevation. Our findings show that increases in temperature intensify predator killing rates, prey consumption, and lipid intake, but the responses to temperature vary between species, which may be a result of species‐specific differences in their hunting behavior and sensitivity to temperature.     

Size and fecundity hierarchies in an herbaceous perennial

Summary Inequalities in size in populations have potentially important effects on fitness but have rarely been examined in natural populations. I measured size (number of culms) and fecundity (number of spikelets) in five populations of the grass Danthonia spicata from 1981 to 1985. The populations were in sites in a Pinus-Quercus-Populus forest in northern lower Michigan, USA comprising a secondary succession sequence. The sites had been burned in 1980, 1954, 1948, 1936, and 1911, respectively. Mean sizes and fecundities and the amount of hierarchy in size and fecundity, measured by the Gini coefficient, were compared between the YOUNG population, 1980 burn site, and the OLD populations, 1954, 1948, 1936, and 1911 burn sites. I found large differences in mean size and fecundity between the YOUNG and OLD populations with much larger individuals in the YOUNG population. No differences in size hierarchies were found in either the first year of measurement or after five years. The fecundity hierarchies showed no significant difference among the populations in the first year but after five years the YOUNG population showed a significant decrease in amount of inequality. The longterm patterns of size and fecundity hierarchies differed because fecundity was a cumulative trait while size was not. Size inequalities may not always be a good measure of fecundity inequalities. Short-term measures of inequality in perennials may not be a good indicator of long-term values. In contrast to greenhouse studies, habitat light levels did not affect size hierarchies although they did affect fecundity hierarchies.     

Food consumption and diet composition of the web-building spider Agelena limbata in two habitats

Summary Prey capture rate, food consumption, and diet composition of all developmental stages of the funnelweb spider Agelena limbata were estimated in woody and open habitats by a sight-count method. Prey availability was evaluated on the basis of two indices, i.e. the ratios of daily food consumption to dry weight of predator and to daily standard metabolic rate. These indices varied seasonally and between instars in this spider. Comparison of these indices between arthropod predators suggests that A. limbata live under conditions of relatively limited food supply. In the open habitat, the spiders reduced foraging activities to avoid heat stress at midday in summer because the sheet web was exposed to the direct rays of the sun and its temperature exceeded 40°C. The daily food consumption of adult spiders in the open habitat was about half of that in the woody habitat. The lower rate of energy intake of spiders in the open habitat may cause the observed smaller size of adults and lower fecundity. A. limbata captured a great range of prey comprising ten orders of arthropods and ate chemically defended insects, e.g. stink bugs, lady beetles, and ants which were rejected by many spiders. This generalistic foraging may be associated with limited and heterogeneous food supply in this spider.     

Retention, capture and consumption of experimental prey by orb-web weaving spiders in coffee plantations of Southern Mexico

This study focuses on the predatory capacity of four sympatric species of web- building spiders that inhabit coffee plantations in Southern Mexico: Gasteracantha cancriformis, Cyclosa caroli, and the morphologically similar species pair Leucauge mariana and L. venusta which were considered as one species group. The retention capabilities of the webs of these species and the incidence of prey capture and consumption were measured using eight types of insect prey belonging to the orders Coleoptera (1 species), Hymenoptera (3), Diptera (2) Lepidoptera (1) and Homoptera (1). The different characteristics of each prey such as body weight, body size, defensive behaviour, etc., were recorded. The incidence of prey retention, capture and consumption were significantly higher in G. cancriformis than in any of the other species. The lowest rates of retention, capture and consumption were observed in C. caroli, while L. mariana/venusta were intermediate in their predatory capabilities. Significant negative correlations between prey size and percent consumption were detected in L. mariana/venusta and in G. cancriformis; in both cases, large prey were less likely to be immediately consumed than small prey items. The results can be interpreted in the light of the morphological characteristics of the spiders. G. cancriformis possesses long legs and a carapace and appeared to have few difficulties to manipulate all types of prey. In contrast, C. caroli showed lesser abilities to manipulate and subdue aggressive prey items, perhaps due to the short leg length and unprotected body of this species. The consumption of prey items may be related to the predatory strategy of each spider. G. cancriformis constructs a new web every morning and prey storage was never observed. The absence of prey storage behaviour could explain why this species consumes prey soon after capture. In contrast, C. caroli constructs a permanent web and stores captured prey on a stabilimentum that may explain the very low incidence of immediate consumption of prey observed in this species.     

An order-specific monoclonal antibody to Diptera reveals the impact of alternative prey on spider feeding behavior in a complex food web

Generalist predators have the capacity to restrict pest population growth, especially early in the season before densities increase. However, their polyphagous feeding habits sometimes translate into reduced pest consumption when they target alternative prey. An order-specific monoclonal antibody was developed to examine the strength of trophic connections between Diptera, a major category of non-pest prey, and linyphiid spiders in alfalfa. We report the development and characterization of a monoclonal antibody with order-level specificity to Diptera. This antibody elicited strong absorbance to 22 Diptera from 13 families, no false-positive reactivity to non-dipteran invertebrates, and antigen detection periods following prey consumption that were comparable between spiders. Over 900 field-collected females of the linyphiid spiders Erigone autumnalis and Bathyphantes pallidus were screened for Diptera antigen. Significantly more B. pallidus screened positive for Diptera (40%) compared to E. autumnalis (16%), indicating differential reliance on these prey. In parallel with the collection of spiders for gut-content analysis, prey availability was estimated at web sites. The two spiders exhibited different feeding responses to prey availability. Consumption of Diptera by B. pallidus was strongly correlated with Diptera abundance whilst the availability of other potential prey did not influence predation rates. Conversely, E. autumnalis did not prey upon Diptera in proportion to availability, but increased Collembola activity-density reduced dipteran consumption. Integration of molecular gut-content analysis with precise sampling of prey demonstrated how two closely related linyphiid spiders exhibit different feeding responses to the availability of prey under natural field conditions. Elucidating the feeding preferences of natural enemies is critical to effective incorporation of biological control by generalist predators in the management of agricultural pests.     

Resource-mediated demographic variation during the midsummer succession of a cladoceran community

SUMMARY. 1. The midsummer succession of cladoceran zooplankton in Lake Texoma was examined by demographic characterization of lake populations and a parallel set of life table experiments in which the dominant cladoceran species were raised on naturally occurring lake phytoplankton at lake temperatures. Diaphanosoma leuchtenbergianum occurred throughout the study period (mid June-mid August 1981) but Daphnia parvula, D. galeata mendotae and Ceriodaphnia lacustris were rarely detected after 15 July.
2. Analyses of size structure and size-specific fecundity of the cladoceran populations showed that (1) size structure shifted to smaller individuals in mid July, (2) size-specific fecundity was relatively constant in the smaller size classes and was constant or declined in larger females of each species, and (3) size at maturation did not vary significantly during the study of any population.
3. Individual growth rates of the two Daphnia species and Ceriodaphnia in the life table experiments were significantly lower in mid July when populations were declining and when size structure of each population was more dominated by smaller Individuals. The reduction in individual growth rates was short-lived in the life table experiments; growth rates returned to pre-decline levels by the end of July.
4. Two effects of temporary reductions in individual growth rates when size-specific fecundity and size at maturation are constant are (1) that size structure is temporarily shifted to smaller individuals, and (2) the potential rate of population growth is reduced because of delays in reproduction. Because data on size structure and size-specific fecundity are commonly used to evaluate the relative effects of predators and resource changes on populations it is noteworthy that erroneous conclusions about the mechanism of population decline may be reached when individual growth rates vary.     

Rain,prey and predators: climatically driven shifts in frog abundance modify reproductive allometry in a tropical snake

To predict the impacts of climate change on animal populations, we need long-term data sets on the effects of annual climatic variation on the demographic traits (growth, survival, reproductive output) that determine population viability. One frequent complication is that fecundity also depends upon maternal body size, a trait that often spans a wide range within a single population. During an eight-year field study, we measured annual variation in weather conditions, frog abundance and snake reproduction on a floodplain in the Australian wet-dry tropics. Frog numbers varied considerably from year to year, and were highest in years with hotter wetter conditions during the monsoonal season (“wet season”). Mean maternal body sizes, egg sizes and post-partum maternal body conditions of frog-eating snakes (keelback, Tropidonophis mairii, Colubridae) showed no significant annual variation over this period, but mean clutch sizes were higher in years with higher prey abundance. Larger females were more sensitive to frog abundance in this respect than were smaller conspecifics, so that the rate at which fecundity increased with body size varied among years, and was highest when prey availability was greatest. Thus, the link between female body size and reproductive output varied among years, with climatic factors modifying the relative reproductive rates of larger (older) versus smaller (younger) animals within the keelback population.     

Variations in Fecundity and Egg Size of Female Nile Tilapia, Oreochromis niloticus, from Man-made Lakes of Côte D'Ivoire

Fecundity and oocyte size of Oreochromis niloticus females were studied over a period of two annual cycles in six small agropastoral and three large hydroelectric reservoirs of Côte d'Ivoire. Important differences in fecundity and oocyte size were observed among populations and within the same population between successive years. An inverse correlation was found between size and number of oocytes produced by females. This inverse relationship occurred for a constant spawn weight during the first year of study, but not during the second year. Monthly mean residuals of regressions between fecundity and female body weight have shown a seasonal variation in fecundity. The peak of fecundity corresponded with the maximum resource availability and the flooding eminence, which may have a great impact on parents and offspring fitness.     

Survival benefits select for group living in a social spider despite reproductive costs

The evolution of cooperation requires benefits of group living to exceed costs. Hence, some components of fitness are expected to increase with increasing group size, whereas others may decrease because of competition among group members. The social spiders provide an excellent system to investigate the costs and benefits of group living: they occur in groups of various sizes and individuals are relatively short-lived, therefore life history traits and Lifetime Reproductive Success (LRS) can be estimated as a function of group size. Sociality in spiders has originated repeatedly in phylogenetically distant families and appears to be accompanied by a transition to a system of continuous intra-colony mating and extreme inbreeding. The benefits of group living in such systems should therefore be substantial. We investigated the effect of group size on fitness components of reproduction and survival in the social spider Stegodyphus dumicola in two populations in Namibia. In both populations, the major benefit of group living was improved survival of colonies and late-instar juveniles with increasing colony size. By contrast, female fecundity, female body size and early juvenile survival decreased with increasing group size. Mean individual fitness, estimated as LRS and calculated from five components of reproduction and survival, was maximized for intermediate- to large-sized colonies. Group living in these spiders thus entails a net reproductive cost, presumably because of an increase in intra-colony competition with group size. This cost is traded off against survival benefits at the colony level, which appear to be the major factor favouring group living. In the field, many colonies occur at smaller size than expected from the fitness curve, suggesting ecological or life history constraints on colony persistence which results in a transient population of relatively small colonies.     

Effects of an experimental increase in prey abundance upon the reproductive rates of two orb-weaving spider species (Araneae: Araneidae)

Summary A field experiment was performed to determine if food is a limited resource for adult females of two species of orb-weaving spiders, Mecynogea lemniscata and Metepeira labyrinthea. Spiders built webs after being added to open experimental units located in a mixed deciduous-pine forest in Maryland, USA. Each unit was a frame supporting dead branches of the type used by both species for anchoring webs. Spiders on half the units were exposed to natural prey densities only, while each spider on the other units was given laboratory-reared flies in order to increase prey availability above natural levels. Supplemental feeding continued for 2.5 months. At the end of the experiment all egg sacs were removed from the units.Providing additional prey did not increase the survival rate on the units (net effect of mortality, emigration and immigration). However, both species responded to additional prey by significantly increasing the number of eggs produced per female, indicating that food was a limited resource for these species. Median egg production per female increased from 34 to 62 for Mecynogea lemniscata and from 65 to 145 for Metepeira labyrinthea. Egg weight was not affected.Feeding rates and nearest neighbor distances were determined for spiders in non-experimental populations, which permitted evaluation of the experiment's naturalness. The effects of food supply upon the reproductive rates of the two species are discussed in relation to their numerical response and population dynamics.     

Density dependence,prey accessibility and prey depletion by fisheries drive Peruvian seabird population dynamics

In marine ecosystems top predator populations are shaped by environmental factors affecting their prey abundance. Coupling top predators’ population studies with independent records of prey abundance suggests that prey fluctuations affect fecundity parameters and abundance of their predators. However, prey may be abundant but inaccessible to their predators and a major challenge is to determine the relative importance of prey accessibility in shaping seabird populations. In addition, disentangling the effects of prey abundance and accessibility from the effects of prey removal by fisheries, while accounting for density dependence, remains challenging for marine top predators. Here, we investigate how climate, population density, and the accessibility and removal of prey (the Peruvian anchovy Engraulis ringens) by fisheries influence the population dynamics of the largest sedentary seabird community (≈ 4 million individuals belonging to guanay cormorant Phalacrocorax bougainvillii, Peruvian booby Sula variegata and Peruvian pelican Pelecanus thagus) of the northern Humboldt Current System over the past half‐century. Using Gompertz state–space models we found strong evidence for density dependence in abundance for the three seabird species. After accounting for density dependence, sea surface temperature, prey accessibility (defined by the depth of the upper limit of the subsurface oxygen minimum zone) and prey removal by fisheries were retained as the best predictors of annual population size across species. These factors affected seabird abundance the current year and with year lags, suggesting effects on several demographic parameters including breeding propensity and adult survival. These findings highlight the effects of prey accessibility and fishery removals on seabird populations in marine ecosystems. This will help refine management objectives of marine ecosystems in order to ensure sufficient biomass of forage fish to avoid constraining seabird population dynamics, while taking into account of the effects of environmental variability.     

Diet and foraging behaviour of huntsman spiders in the Namib dunes (Araneae: Heteropodidae)

Diet and foraging behaviour of three species of burrowing huntsman spiders, Leucorchestris arenicola, L. steyni and Carparachne aureoflava , from the Namib dunes were investigated over a three-year period. These nocturnal spiders are polyphagous predators that prey on more than 97 species of insects, arachnids and reptiles. Most prey were nocturnal or crepuscular tenebrionid beetles, moths and weevils. Diet varied regionally owing to faunal differences, but was relatively constant over seasons. Although spiders occasionally captured prey greater than themselves, average prey length was about two-thirds their own length. Prey size was not strongly related to spider size. Larger spiders were both cannibals and intraguild predators. Foraging pattern of L. arenicola was variable with several nights of activity followed by one or several nights of rest. Spiders foraged within 3 m of the burrow, but occasionally pursued prey or neighbouring conspecifics further. Large prey (> 3 mm) were captured approximately every five weeks in summer and every seven weeks in winter, producing an average annual consumption of ≅ 10 prey/spider. Namib huntsmen are sit-and-wait predators within narrow territories waiting for the fortuitous arrival of prey and are thus unlikely to limit prey populations. They compensate for food shortages by cannibalism, thus restricting their own population.     

CHAOBORUS PREDATION AND LIFE-HISTORY EVOLUTION IN DAPHNIA PULEX: TEMPORAL PATTERN OF POPULATION DIVERSITY,FITNESS, AND MEAN LIFE HISTORY

The effect of predation by the aquatic dipteran larva Chaoborus americanus on genetic diversity and life-history evolution in the cladoceran Daphnia pulex was investigated in large replicate laboratory populations. Instantaneous daily loss rates of clonal diversity and genetic variance for fitness indicate that 93–99% of initial genetic diversity can be removed from populations during the 8–12 generations of clonal reproduction that occur each year in natural populations. In the absence of predation, the principal evolved changes in mean population life history were smaller immature body size and increased and earlier fecundity. In the presence of size-selective Chaoborus predation, populations evolved toward larger body size and increased and earlier reproduction. The difference between these two trajectories is an estimate of the direct additive effect of Chaoborus predation. This effect was manifested as evolution toward larger body size with a trend toward earlier and increased reproduction.     

Estimating susceptibility of biological control agents to pesticides: influence of life history strategies and population structure

In this study we examined the influences that differing life history strategies and population structures at the time of pesticide exposure have on population susceptibility to pesticides. We used life table data and a matrix projection model to incorporate combinations of mortality (lethal effect) and reductions in fecundity (sublethal effect) into estimates of intrinsic population growth rates (r) for a predator, the seven-spot lady beetle, Coccinella septempunctata L., and its prey, the pea aphid, Acyrthosiphon pisum Harris, and an aphid parasitoid, Diaeretiella rapae (M’Intosh). All three species exhibited differences in key life history variables. The aphid had the highest r and shortest generation time, the ladybeetle had the lowest r and longest generation, while the parasitoid exhibited intermediate life history characteristics. When the model was run with populations started as neonates (aphids) or eggs (lady beetle, parasitoid) for each species, ladybeetle populations were much more susceptible than either aphid or parasitoid populations 30 days after simulated exposure to a pesticide. For example, 50% mortality and a 50% reduction in fecundity resulted in a population headed toward extinction (negative r) for the ladybeetle while the parasitoid population grew exponentially (positive r) even after sustaining 70% mortality and a 70% reduction in fecundity. The aphid species maintained exponential growth after sustaining 80% mortality and an 80% reduction in fecundity. Thus, differences in life history variables accounted for the greater susceptibility of the ladybeetle to a pesticide than its aphid prey or the parasitoid over a set time interval. These differences in susceptibility were greatly reduced when the model was run starting with a mixed age/stage population (the stable age distribution) for each species indicating that population structure at the time of pesticide exposure plays a critical role in population susceptibility. These results suggest that life history attributes as well as population structure at the time of pesticide exposure both play a major role in population susceptibility to pesticides, highlighting the need to explicitly consider differences in life history variables among species when calculating compatibility of pesticides and biological control agents as well as the population structure of beneficial species at the time of pesticide application.     

Nutritional implications for sexual cannibalism in a sexually dimorphic orb web spider

Models predicting mechanisms driving sexual cannibalism in spiders with sexual size dimorphism (SSD) often assume that spiders use post‐copulatory food to channel nutrients into eggs and fecundity is altered through changes in clutch size or egg mass. I tested these assumptions using an orb web spider with extreme SSD, Argiope keyserlingi. I fed mated female spiders prey of either high protein‐low energy or low protein‐high energy composition. I measured egg energy density; a measure of the relative volumes of yolk and albumen. I predicted that if A. keyserlingi increase their egg energy density upon feeding on prey of a specific nutrient composition, they could enhance their fecundity by investing in more energy dense eggs. However, if the egg energy densities are dissimilar to their post‐copulatory prey they must be drawing energy from their somatic reserves to invest in eggs. In a further experiment I allowed female spiders to mate with and cannibalize males to determine if cannibalism induces similar effects on egg energy density. Male spider protein energy ratio was measured and found to resemble the high protein‐low energy prey. I found disagreement between the composition of post‐copulatory food and eggs in both experiments. Additionally, spiders fed high protein‐low energy prey lost weight indicating that they draw on their energy reserves to invest in eggs. I thus concluded that spiders that feed on high protein‐low energy prey or on males increase their egg energy density and, possibly, fecundity. However, the nutrient content of the prey or males cannot provide for investment in eggs. The energy invested in eggs is drawn from somatic reserves, probably induced by an as yet undescribed physiological trigger.     

Prey Capture Behaviour in the Social Spider Anelosimus eximius (Araneae: Theridiidae): Responses to Prey Size and Type

Some species of web building spiders use different capture tactics for different prey types. The main factors influencing the attack behaviour are the ability of the insect to escape, the risks of injury to the spiders and prey size. This study evaluated the effects of size and prey type on prey capture behaviour of the social spider Anelosimus eximius as influenced by the number of spiders attracted by prey movements that did not bite until the immobilization (bystanders) and the number of spiders that contributed to prey immobilization (catchers). We carried out a two‐factor (prey size and type) experiment offering prey belonging to four orders: Diptera, Lepidoptera, Hymenoptera and Orthoptera, in a size gradient within each prey type. Both factors influenced the number of spiders recruited as bystanders, but only prey body size influenced the number of catchers in the subduing process. The possible advantages of the presence of bystanders around the interception site are discussed.