Variable dependence on detrital and grazing food webs by generalist predators: aerial insects and web spiders

Recent studies have shown that organisms from the detritus food web subsidize generalist predators in aboveground food webs, but its significance in space and time is largely unknown. Here we report seasonal dynamics of aerial insects from grazing and detritus food webs in both forest and grassland habitats, and show how these patterns influence the dependence of web spiders on the detritus food web. Detrital insects were more abundant in spring, decreased in summer, and then increased slightly in autumn. This pattern was most conspicuous in Nematocera. Due to different seasonal activity patterns of grazing and detrital insects, the proportion of detrital insects was greater in spring and autumn. Detrital insects were relatively more abundant in the forest than in the grassland. Prey captured by web spiders generally reflected seasonal and spatial patterns of aerial insect abundance. In particular, Leucauge spiders reversed their dependence on the two food webs seasonally. Body size of spiders was negatively correlated with the proportion of detrital prey, suggesting that the detrital subsidy is essential for relatively small predators. This size effect probably resulted from interaction of the following two factors: 1) the maximum body size of prey that can be caught increased with spider body size, 2) larger body size classes of aerial insects included a higher proportion of insects from the grazing food web.     

Prey selection by linyphiid spiders: molecular tracking of the effects of alternative prey on rates of aphid consumption in the field

A molecular approach, using aphid-specific monoclonal antibodies, was used to test the hypothesis that alternative prey can affect predation on aphids by linyphiid spiders. These spiders locate their webs in cereal crops within microsites where prey density is high. Previous work demonstrated that of two subfamilies of Linyphiidae, one, the Linyphiinae, is web-dependent and makes its webs at sites where they were more likely to intercept flying insects plus those (principally aphids) falling from the crop above. The other, the Erigoninae, is less web-dependent, making its webs at ground level at sites with higher densities of ground-living detritivores, especially Collembola. The guts of the spiders were analysed to detect aphid proteins using enzyme-linked immunosorbent assay (ELISA). Female spiders were consuming more aphid than males of both subfamilies and female Linyphiinae were, as predicted, eating more aphid than female Erigoninae. Rates of predation on aphids by Linyphiinae were related to aphid density and were not affected by the availability of alternative prey. However, predation by the Erigoninae on aphids was significantly affected by Collembola density. Itinerant Linyphiinae, caught away from their webs, contained the same concentration of aphid in their guts as web-owners. However, nonweb-owning Erigoninae, living away from Collembola aggregations at web-sites, contained significantly higher concentrations of aphid. For both subfamilies there was evidence of a disproportionate increase in predation on aphids once Collembola populations had declined. It was concluded that nonaphid prey, by helping to maintain spiders in the field, can significantly affect predation on aphids.     

Collembola as alternative prey sustaining spiders in arable ecosystems: prey detection within predators using molecular markers

Collembola comprise a major source of alternative prey to linyphiid spiders in arable fields, helping to sustain and retain these predators as aphid control agents within the crop. Polymerase chain reaction primers were developed for the amplification, from spider gut samples, of DNA from three of the most abundant species of Collembola in wheat crops in Europe, namely Isotoma anglicana, Lepidocyrtus cyaneus and Entomobrya multifasciata. The primers amplified fragments of the mitochondrial cytochrome oxidase subunit I (COI) gene and were designed following alignment of comparable sequences for a range of predator and prey species. Each of the primer pairs proved to be species-specific to a Collembola species, amplifying DNA fragments from 211 to 276 base pairs in length. Following consumption of a single collembolan, prey DNA was detectable in 100% of spiders after 24 h of digestion. We report the first use of DNA-based techniques to detect predation by arthropods on natural populations of prey in the field. All three species of Collembola were consumed by the spiders. By comparing the ratios of the Collembola species in the field with the numbers of spiders that gave positive results for each of those species, it was possible to demonstrate that the spiders were exercising prey choice. Overall, a single target species of Collembola was eaten by 48% of spiders while a further 16% of spiders contained DNA from two different species of Collembola. Preference was particularly evident for I. anglicana, the species most frequently found in spider guts yet the least numerous of the three target species in the field.     

Contributions of detrital subsidies to aboveground spiders during secondary succession, revealed by radiocarbon and stable isotope signatures

Prey subsidies originating from detritus add nutrients and energy to arboreal communities. Measurement of this subsidy is required in the understanding of how food web dynamics respond to changes in surrounding environments. Shrub spiders are one of the key predators involved in food web coupling. We evaluate the effects of potential changes in prey availabilities during secondary succession on the contribution of subsidy from detrital food webs to shrub spiders and how different spider feeding guilds used the subsidy of prey from detrital food webs. We measured the relative importance of the subsidy for the spider feeding guilds, using the ratios of stable isotopes of C (δ¹³C), and N (δ¹⁵N) and C isotope discrimination (Δ¹⁴C). Diet age was calculated from Δ¹⁴C values, because old diet ages of spiders indicate that the spiders consume prey from detrital food sources. Dominant aerial prey (Diptera) had a distinctively old diet age compared with arboreal prey, which indicates that aerial prey were subsidized from detrital food webs. Sit-and-wait spiders tended to have an older diet age than active hunting spiders, which indicates that sit-and-wait spiders depended more on subsidies. Diet age varied only slightly for spiders in stands of different ages, indicating that rates at which spiders use grazing and detrital prey are probably determined more by foraging strategies and not by stand age. A dominance of sit-and-wait predators will lead to higher detrital subsidy inputs in shrub habitats. This study highlights the effect of shrub spider community structure (feeding guild composition) on the volume of the subsidy received from the detrital food web.     

Pollen interception by linyphiid spiders in a corn agroecosystem: implications for dietary diversification and risk-assessment

Dietary diversification, including consumption of plant tissues such as pollen, can enhance the fecundity of generalist predators, resulting in improved control of pest prey. Supplemental pollen feeding has been observed in many natural enemies, including sheet-web spiders (Araneae: Linyphiidae), which represent a major component of food webs in agroecosystems. Their horizontal, ground-based webs have the potential to intercept pollen grains during anthesis of crop plants, providing the opportunity for consumption of pollen to occur. In laboratory feeding trials, Frontinella communis and Tennesseellum formicum (Araneae: Linyphiidae) readily fed on pollen grains dusted on their webs, with 82 and 92% of spiders consuming pollen within the 210 min trial. These results revealed a strong potential for dietary supplementation with pollen in ground-based sheet-web spiders, indicating that pollen feeding may be an important component of the feeding biology of linyphiids. To measure pollen and prey interception in simulated linyphiid webs, a 20 m × 20 m grid of miniature sticky traps was established within and downwind of a corn agroecosystem. Traps were exposed for 24 h, all intercepted material was transferred to the laboratory for subsequent identification, and replaced with additional traps for 28 consecutive days in July and August 2008, to encompass periods before, during and after anthesis. Over 150,000 corn pollen grains and 5,000 prey items (dominated by Collembola and Hemiptera) were intercepted at simulated web-sites. Dates of peak anthesis resulted in pollen counts as high as 4,000 grains per web-site in the interior of the cornfield. Spatial Analysis by Distance Indices (SADIE) indicated significant temporal and spatial variability in pollen interception within and outside the corn field, but interestingly there was no significant spatial association between pollen and prey. Furthermore, transgenic Bacillus thuringiensis corn expresses insecticidal proteins in pollen, posing an exposure risk to non-target arthropods. Consumption of corn pollen may be a route to transgenic protein exposure in this important taxon of generalist predators.     

Prey use by web-building spiders: stable isotope analyses of trophic flow at a forest-stream ecotone

A forest-stream trophic link was examined by stable carbon isotope analyses which evaluated the relationship of aquatic insects emerging from a stream to the diets of web-building spiders. Spiders, aquatic and terrestrial prey, and basal resources of forest and stream food webs were collected in a deciduous forest along a Japanese headwater stream during May and July 2001. The ¹³C analyses suggested that riparian tetragnathid spiders relied on aquatic insects and that the monthly variation of such dependence is partly associated with the seasonal dynamics of aquatic insect abundance in the riparian forest. Similarly, linyphiid spiders in the riparian forest exhibited ¹³C values similar to aquatic prey in May. However, their ¹³C values were close to terrestrial prey in both riparian and upland (150m away from the stream) forests during June to July, suggesting the seasonal incorporation of stream-derived carbon into their tissue. In contrast, araneid spiders relied on terrestrial prey in both riparian and upland forests throughout the study period. These isotopic results were consistent with a previous study that reported seasonal variation in the aquatic prey contribution to total web contents for each spider group in this forest, implying that spiders assimilate trapped prey and that aquatic insect flux indeed contributes to the energetics of riparian tetragnathid and linyphiid spiders.     

Multitrophic effects of nutrient addition in upland grassland

Although the effects of nutrient enhancement on aquatic systems are well documented, the consequences of nutritional supplements on soil food webs are poorly understood, and results of past research examining bottom-up effects are often conflicting. In addition, many studies have failed to separate the effects of nutrient enrichment and the physical effects of adding organic matter. In this field study, we hypothesised that the addition of nitrogen to soil would result in a trophic cascade, through detritivores (Collembola) to predators (spiders), increasing invertebrate numbers and diversity.Nitrogen and lime were added to plots in an upland grassland in a randomised block design. Populations of Collembola and spiders were sampled by means of pitfall traps and identified to species.Seventeen species of Collembola were identified from the nitrogen plus lime (N+L) and control plots. Species assemblage, diversity, richness, evenness and total number were not affected by nutrient additions. However, there was an increase in the number of Isotomidae juveniles and Parisotoma anglicana trapped in the N+L plots.Of the 44 spider species identified, over 80% were Linyphiidae. An effect on species assemblage from the addition of N+L to the plots was observed on two of the four sampling dates (July 2002 and June 2003). The linyphiid, Oedothorax retusus, was the only species significantly affected by the treatments and was more likely to be trapped in the control plots.The increased number of juvenile Collembola, and change in community composition of spiders, were consequences of the bottom-up effect caused by nutrient inputs. However, despite efforts to eliminate the indirect effects of nutrient inputs, a reduction in soil moisture in the N+L plots cannot be eliminated as a cause of the invertebrate population changes observed. Even so, this experiment was not confounded by the physical effects of habitat structure reported in most previous studies. It provides evidence of moderate bottom-up influences of epigeic soil invertebrate food webs and distinguishes between nutrient addition and plant physical structure effects. It also emphasises the importance of understanding the effects of soil management practices on soil biodiversity, which is under increasing pressure from land development and food production.     

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.     

Various competitive interactions explain niche separation in crop‐dwelling web spiders

Competition for resources is a major organizing principle in communities of organisms that share similar ecological niches. Niche separation by means of exploitation or interference competition was investigated in two taxa of crop‐inhabiting spiders that overlap in microhabitat use and have similar web design. Competition for prey and web sites was tested in microcosm experiments with the most common species that build sheet‐webs: Enoplognatha gemina (Theridiidae) and Alioranus pastoralis (Linyphiidae). A field survey over the crop season provided data on spatial and temporal dispersion of Enoplognatha spp. (Theridiidae) and linyphiid spiders (Linyphiidae) and on availability of prey over the season. In the microcosm experiments, both taxa took springtails as prey, but only Enoplognatha fed on aphids. Differences in diet, however, could not be attributed to either exploitative or interference competition. Spatial separation of websites was attained by vertical displacement of webs in the vegetation (Enoplognatha) and by avoidance of patches occupied by conspecific or heterospecific individuals (linyphiids). In the field, densities of linyphiids and Enoplognatha were correlated negatively and webs were over‐dispersed relative to a random distribution. Both taxa colonized the field at the start of the season; linyphiids colonized as adults, quickly reproduced, and had a second adult peak; Enoplognatha matured in the middle of the season and their numbers remained fairly constant over the season. The combined experimental manipulations and field data suggest that niche separation occurs at different scales. The hypothesis of competition for websites was partially supported, while prey preference (or tolerance) and temporal differences in life history stages also may explain the negative correlations between densities of the two taxa.     

Web-site selection strategies of linyphiid spiders in alfalfa: implications for biological control

Site-specific foraging can enhance the ability of generalist predators to provide effective and sustainable levels of pest control in agroecosystems. This can result from increased growth rates, higher population densities, and improved capture frequencies of pests at high prey density microsites. We tested the hypothesis that linyphiid spiders would exhibit microhabitat-specific web-site selection strategies in alfalfa. This was predicted to result in high prey densities at web-sites compared to paired non-web-sites through direct, or indirect, selection of prey-rich habitats. A total of 22,242 potential prey items were collected from mini-sticky traps located at 896 microsites. Web-centered mini-sticky traps on the ground, representative of Erigone autumnalis Emerton (Araneae: Linyphiidae) webs, captured similar numbers of potential prey as paired non-web-centered traps nearby. However, aerial sticky traps at web-sites of Bathyphantes pallidus (Banks) (Araneae: Linyphiidae) contained significantly more Diptera and Empoasca fabae (Harris) (Homoptera: Cicadellidae) than paired non-web-centered sticky-traps. Prey activity-densities also varied between web-sites of E. autumnalis and B. pallidus. Diptera were dominant at aerial microsites of B. pallidus whilst Collembola were abundant on ground-based traps of E. autumnalis. These results suggest that in alfalfa, the pressure for selecting prey-rich web-sites by erigonine spiders is low, but B. pallidus exhibits a selective web-location strategy targeted towards high quality dipteran prey. These sites also captured large numbers of E. fabae, a major pest of alfalfa, thus implicating aerial-based linyphiines as valuable predators in biological control.     

Trophic structure of the spider community of a Mediterranean citrus grove: A stable isotope analysis

Spiders are dominant terrestrial predators that consume a large variety of prey and engage in intraguild predation. Although the feeding habits of certain species are well known, the trophic structure of spider assemblages still needs to be investigated. Stable isotope analysis enables characterisation of trophic relationships between organisms because it tracks the energy flow in food webs and indicates the average number of trophic transfers between a given species and the base of the web, thus being a useful tool to estimate the magnitude of intraguild predation in food webs. Using this technique, we studied the trophic groups of spiders and their links within the arthropod food web of a Mediterranean organic citrus grove. We assessed the trophic positions of the 25 most common spider species relative to other arthropod predators and potential prey in the four seasons of the year, both in the canopy and on the ground. The analyses showed great seasonal variation in the isotopic signatures of some arthropod species, as well as the existence of various trophic groups and a wide range of trophic levels among spiders, even in species belonging to the same family. Differences in δ¹⁵N between spiders and the most abundant prey in the grove usually spanned two trophic levels or more. Our findings provide field evidence of widespread intraguild predation in the food web and caution against using spider families or guilds instead of individual species when studying spider trophic interactions.     

Potential positive effect of the ant species Lasius niger on linyphiid spiders

Ants are highly abundant generalist predators and important ecosystem engineers which can strongly affect the composition of animal communities. We manipulated the density of the ant species Lasius niger with baits in a small‐scale field experiment to study the role of intraguild predation, top‐down control and bottom‐up effects of ants in a dry grassland surrounded by agricultural fields. Two different kinds of baits (honey and tuna) were presented near to the nests and at a distance of 2 m from six L. niger colonies in a dry grassland habitat, where L. niger was a highly abundant, omnipresent species. The experiments were performed for 1 month in spring. Additionally, the natural abundance of L. niger varying with the distance to their nests was used to study the effects on spiders and potential prey groups. The activity of L. niger was significantly higher at tuna baits compared with that at honey baits and empty control dishes. We found no effects of higher activity of L. niger on the arthropod community. However, there is evidence for a facilitation effect of ants on Collembola near to their colonies, probably due to habitat modification, which also influenced the density of Linyphiidae. Both groups had up to four times higher denisities next to L. niger colonies than at a distance of 2 m. Furthermore, δ¹³C values demonstrated that linyphiid spiders and L. niger predominantly feed on Collembola. We conclude that there is no evidence of top‐down effects of L. niger in a grassland in spring, but we found a facilitation of linyphiid spiders and their prey by the ants, which acted as ecosystem engineers.     

Evidence of exploitative competition among young stages of the wolf spider Schizocosa ocreata

Summary Previous research by many investigators has demonstrated food limitation in both web-building and wandering spiders. Field experiments have tested for exploitative competition for prey in web-building, but not wandering species. As a first step to examining the question of whether spiders without webs exhibit exploitative competition, we manipulated densities of young stages of a common wolf spider, Schizocos ocreata, and measured (1) spider growth rate and (2) numbers of Collembola, a potential prey organism. Replicate populations of recently hatched S. ocreata were established in 1-m² fenced plots at four levels: 0×, 0.25×, 1× and 4× natural density. Increasing spider density had a negative effect on spider growth rate, defined as increase in weight or cephalothorax width. Early in the experiment spider density had a weak negative effect on Collembola numbers [p(F)=0.08]. Taken together, this probable response by Collembola and the clear effect of spider density on growth rate constitute the first experimental evidence of intraspecific exploitative competition for prey in a species of wandering spider. We discuss (1) the strength of this evidence given the constraints of the experiment's design, and (2) the implications of the strong convergence in spider densities that had occurred after 2.5 months.     

Intraguild interactions between spiders and ants and top-down control in a grassland food web

In most terrestrial ecosystems ants (Formicidae) as eusocial insects and spiders (Araneida) as solitary trappers and hunters are key predators. To study the role of predation by these generalist predators in a dry grassland, we manipulated densities of ants and spiders (natural and low density) in a two-factorial field experiment using fenced plots. The experiment revealed strong intraguild interactions between ants and spiders. Higher densities of ants negatively affected the abundance and biomass of web-building spiders. The density of Linyphiidae was threefold higher in plots without ant colonies. The abundance of Formica cunicularia workers was significantly higher in spider-removal plots. Also, population size of springtails (Collembola) was negatively affected by the presence of wandering spiders. Ants reduced the density of Lepidoptera larvae. In contrast, the abundance of coccids (Ortheziidae) was positively correlated with densities of ants. To gain a better understanding of the position of spiders, ants and other dominant invertebrate groups in the studied food web and important trophic links, we used a stable isotope analysis (¹⁵N and ¹³C). Adult wandering spiders were more enriched in ¹⁵N relative to ¹⁴N than juveniles, indicating a shift to predatory prey groups. Juvenile wandering and web-building spiders showed δ¹⁵N ratios just one trophic level above those of Collembola, and they had similar δ¹³C values, indicating that Collembola are an important prey group for ground living spiders. The effects of spiders demonstrated in the field experiment support this result. We conclude that the food resource of spiders in our study system is largely based on the detrital food web and that their effects on herbivores are weak. The effects of ants are not clear-cut and include predation as well as mutualism with herbivores. Within this diverse predator guild, intraguild interactions are important structuring forces.     

Substrate Availability May Be More Important than Aquatic Insect Abundance in the Distribution of Riparian Orb-web Spiders in the Tropics

Spiders that are abundant along streams may depend on energy subsidies across land–water ecotones, but the effects of season and habitat structure on this trophic linkage remain poorly understood in the tropics. We carried out surveys and a manipulative experiment to investigate the effects of season and substrate availability on the distribution of riparian orb-web spiders in Hong Kong, southern China. In the surveys, spider abundance, prey, substrate use, and web orientation were recorded. The experiment involved installation of in-stream artificial substrates (ropes and bamboo poles) to increase substrate availability for web attachment. We found no seasonal difference in web abundance, but seasonal differences were observed for the prey on webs: aquatic insects (mostly Ephemeroptera and chironomid midges) contributed 69 percent of total prey collected during the wet season, but only 38 percent during the dry season. Most webs (50–80%) were < 0.5 m above the water and 45–51 percent of them tended to be orientated horizontally to the water surface and supported by overhanging vegetation and boulders. The addition of artificial substrates resulted in a 23–34 percent increase in the number of webs at the four treatment sites compared to controls, indicating that availability of web-building substrates is a critical determinant of the spider distribution. Our results suggest that riparian zones are potential 'hotspots' of food availability for spiders, and that the aquatic insect subsidy allows this habitat to support increased densities of spiders when the constraint of substrate availability is relaxed.     

Selectivity underlies the dissociation between seasonal prey availability and prey consumption in a generalist predator

Generalist predators are capable of selective foraging, but are predicted to feed in close proportion to prey availability to maximize energetic intake especially when overall prey availability is low. By extension, they are also expected to feed in a more frequency‐dependent manner during winter compared to the more favourable foraging conditions during spring, summer and fall seasons. For 18 months, we observed the foraging patterns of forest‐dwelling wolf spiders from the genus Schizocosa (Araneae: Lycosidae) using PCR‐based gut‐content analysis and simultaneously monitored the activity densities of two common prey: springtails (Collembola) and flies (Diptera). Rates of prey detection within spider guts relative to rates of prey collected in traps were estimated using Roualdes’ c_st model and compared using various linear contrasts to make inferences pertaining to seasonal prey selectivity. Results indicated spiders foraged selectively over the course of the study, contrary to predictions derived from optimal foraging theory. Even during winter, with overall low prey densities, the relative rates of predation compared to available prey differed significantly over time and by prey group. Moreover, these spiders appeared to diversify their diets; the least abundant prey group was consistently overrepresented in the diet within a given season. We suggest that foraging in generalist predators is not necessarily restricted to frequency dependency during winter. In fact, foraging motives other than energy maximization, such as a more nutrient‐focused strategy, may also be optimal for generalist predators during prey‐scarce winters.     

Subsidy from the detrital food web, but not microhabitat complexity, affects the role of generalist predators in an aboveground herbivore food web

The activity and density of generalist predators, such as carabid beetles, rove beetles and spiders, may increase in response to: (1) increased availability of prey from the belowground subsystem and/or (2) enhanced complexity of aboveground vegetation. Organic farming practices support decomposer populations and enhance habitat complexity due to an increased weed density. A response by generalist predators to such below‐ or aboveground changes could affect predation rates on herbivores in the aboveground food web. We tested this hypothesis in a replicated field experiment conducted in a winter wheat field, where increased predator activity could lead to improved control of herbivorous pests. In a crossed design, we increased and lowered densities of decomposer prey, and manipulated vegetation complexity using artificial plants in order to examine the effect of structural complexity in isolation from effects of plant‐attracted additional prey. Isotomid Collembola exhibited lowest activity‐densities (AD) in plots treated with soil insecticide and had gradually increasing AD in untreated plots and plots receiving detrital subsidies. Carabid beetles and cursorial spiders did not respond to increased availability of isotomid prey, and they unexpectedly displayed higher AD in the structurally less‐complex plots. Aphid density mirrored the positive response of isotomids to detrital subsidies, suggesting that aphids benefited from reduced predation due to predators switching to abundant prey in the decomposer subsystem. The absence of a numerical response by surface‐active predators apparently strengthened this indirect effect of isotomids on aphids. Our results suggest that indirect predator‐mediated prey‐prey interactions can reduce beneficial effects of detrital subsidies on pest suppression. We further demonstrated that generalist predators may not per se benefit from structural complexity. Both results document the challenges associated with management practices that support generalist predators, as these measures may not necessarily improve herbivore suppression.     

The non-filter function of orb webs in spiders

Summary Experiments with artificial webs show that there is no correlation between prey size and mesh width. The number of prey items per thread increases with mesh width. Spiders with narrow-meshed webs catch more prey, whilst spiders with wide-meshed webs save more spinning material.     

Evidence for competition between carnivorous plants and spiders

Several studies have demonstrated that competition between disparate taxa can be important in determining community structure, yet surprisingly, to our knowledge, no quantitative studies have been conducted on competition between carnivorous plants and animals. To examine potential competition between these taxa, we studied dietary and microhabitat overlap between pink sundews (Drosera capillaris) and wolf spiders (Lycosidae) in the field, and conducted a laboratory experiment examining the effects of wolf spiders on sundew fitness. In the field, we found that sundews and spiders had a high dietary overlap with each other and with the available arthropod prey. Associations between sundews and spiders depended on spatial scale: both sundews and spiders were found more frequently in quadrats with more abundant prey, but within quadrats, spiders constructed larger webs and located them further away from sundews as the total sundew trapping area increased, presumably to reduce competition. Spiders also constructed larger webs when fewer prey were available. In the laboratory, our experiment revealed that spiders can significantly reduce sundew fitness. Our findings suggest that members of the plant and animal kingdoms can and do compete.