Alternative predatory tactics of an araneophagic assassin bug (Stenolemus bituberus)

Predators of dangerous prey risk being injured or killed in counter-attacks and hence may use risk-reducing predatory tactics. Spiders are often dangerous predators to insects, but for a few, including Stenolemus bituberus assassin bugs, web-building spiders are prey. Despite the dangers of counter-attack when hunting spiders, there has been surprisingly little investigation of the predatory tactics used by araneophagic (spider-eating) insects. Here, we compare the pursuit tendency, outcome and predatory tactics of S. bituberus against five species of web-building spider. We found that S. bituberus were most likely to hunt and capture spiders from the genus Achaearanea, a particularly common prey in nature. Capture of Achaearanea sp. was more likely if the prey spider was relatively small, or if S. bituberus was in poor condition. S. bituberus used two distinct predatory tactics, ‘stalking’, in which they slowly approached the prey, and ‘luring’, in which they attracted spiders by manipulating the web to generate vibrations. Tactics were tailored to the prey species, with luring used more often against spiders from the genus Achaearanea, and stalking used more often against Pholcus phalangioides. The choice of hunting tactic used by S. bituberus may reduce the risk posed by the prey spider.     

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.     

Prey capture tactics of spiders: An analysis based on a simulation model for spider's growth

The prey capture tactics of spiders was analyzed, considering the energy gained by the capture of prey and that required for it. For the purpose of it, a growth model of spiders was constructed, expressing the flow rate of prey biomass to the spider's body by differential equations. Solving these equations under the differing values of three parameters, growth curves of spiders was obtained. These three parameters are the amount of prey biomass supplied daily to spiders, x₀, the rate of prey capture of spiders, α, and a coefficient of the respiration rate required for the capture of prey, k. When the value of k increased, spiders could grow only at high value of x₀. These results suggest that habitats with small prey biomass are preferred by spiders adopting a sit-and-wait tactics for prey capture, which requires small values of k. Wolf spiders are one of these spiders showing that tactics. On the other hand, web-builders which require large amount of energy for spinning webs (namely, take large value of k), are able to grow only in the habitats with large prey biomass. Each species of spiders are considered to locate in a certain point between both extremes of these tactics for the capture of prey.     

The feeding behaviour of New Zealand Dolomedes species (Araneae: Pisauridae)

Abstract

The prey spectrum and predatory behaviour of Dolomedes sp. (‘D. III’), D. aquaticus, and D. minor are described from a series of field and laboratory investigations, the former made around Nelson and on Banks Peninsula, Canterbury, during summer months. All species are large, robust spiders that capture prey by directly seizing it in their mouthparts, not using silk at any stage of predation. Adult aquatic insects are their main prey, but these are available only irregularly during their activity period (night-time), and the spiders are opportunistic in their feeding habits. They will eat virtually any available small animal, and at least the largest species, D. III, is able to capture and ingest small fishes. Dead as well as live organisms are taken. Furthermore, the spiders are capable of feeding infrequently; when feeding on small prey organisms they may capture several sequentially, to increase the size of the meal. Live prey is caught while it is in flight, or on the ground, or at the water surface (rarely submerged), and is detected primarily by touch and airborne sound; vision is unnecessary for normal predation. Prey is captured very rapidly, even though this may initially involve a dash of up to 40 cm across the water surface to locate the organism. Stages in the behaviour of an active spider, from waiting for prey to grooming after ingestion, are described.     

Prey use of the fishing spider Dolomedes triton (Pisauridae,Araneae): an important predator of the neuston community

Summary Prey of feeding juvenile and adult Dolomedes triton (Walckenaer 1837) were sampled over two seasons on three small ponds in central Alberta, Canada. Prey were mainly insects active at the water surface with truly aquatic species making up about 14% of the diet. Throughout the season aquatic and semi-aquatic Heteroptera represented about 30% of the prey. Diptera and adult Odonata were also important prey items but their abundance in the diet was more variable seasonally. Of the 625 prey items recorded nearly 50% were represented by taxa taken no more than once by spiders in one of the five size classes (adult females, adult males, large, intermediate and small juveniles). Large spiders did not take the smallest prey available, although small and intermediate-sized spiders fed on nearly the full size range taken by larger spiders. Cannibalism was common, accounting for 5% of the observations, with females and large juveniles as the most frequently observed cannibals. We hypothesize that intraguild predation (including cannibalism) could be an important coevolutionary force structuring phenology, population dynamics and microhabitat use of the predatory guild of the neuston community.     

Chaoborus americanus predation on various zooplankters; Functional response and behavioral observations

Summary Predation rates for Chaoborus americanus on different types of noncyclomorphic zooplankton prey were determined in the laboratory as a function of both prey species and density. The sequence of events leading to consumption of prey was also observed, and probabilities determined for the various components.Predation rates generally reached an upper limit as the density of prey increased to high levels. Larger prey were always less vulnerable to Chaoborus predation. Among the species of zooplankton prey examined Holopedium gibberum suffered the lowest rates of predation, while those of the other plankters (Daphnia pulex, D. rosea, Moina hutchinsoni, Diaptomus birgei, D. leptopus, Cyclops vernalis) were approximately equivalent for any given size category.Observation of the predatory sequence indicates that for all the plankters except H. gibberum there were relatively high rates of evasion of attack by C. americanus and low rates of escape after capture. For H. gibberum the situation was reversed, and escape after capture was particularly important in determining the predation rate.The gelatinous envelope of Holopedium gibberum seems to operate as an effective anti-predator device which reduces the likelyhood of retention by Chaoborus after contact has been made.     

The Nutritional Content of Prey Affects the Foraging of a Generalist Arthropod Predator

While foraging theory predicts that predatory responses should be determined by the energy content and size of prey, it is becoming increasingly clear that carnivores regulate their intake of specific nutrients. We tested the hypothesis that prey nutrient composition and predator nutritional history affects foraging intensity, consumption, and prey selection by the wolf spider, Pardosa milvina. By altering the rearing environment for fruit flies, Drosophila melanogaster, we produced high quality flies containing more nitrogen and protein and less lipid than low quality fruit flies. In one experiment, we quantified the proportion of flies taken and consumption across a range of densities of either high or low quality flies and, in a second experiment, we determined the prey capture and consumption of spiders that had been maintained on contrasting diets prior to testing. In both cases, the proportion of prey captured declined with increasing prey density, which characterizes the Type II functional response that is typical of wolf spiders. Spiders with similar nutritional histories killed similar numbers of each prey type but consumed more of the low quality prey. Spiders provided high quality prey in the weeks prior to testing killed more prey than those on the low quality diet but there was no effect of prior diet on consumption. In the third experiment, spiders were maintained on contrasting diets for three weeks and then allowed to select from a mixture of high and low quality prey. Interestingly, feeding history affected prey preferences: spiders that had been on a low quality diet showed no preference but those on the high quality diet selected high quality flies from the mixture. Our results suggest that, even when prey size and species identity are controlled, the nutritional experience of the predator as well as the specific content of the prey shapes predator-prey interactions.     

Predatory Versatility in Females of the Scorpion <Emphasis Type="Italic">Bothriurus bonariensis</Emphasis> (Scorpiones: Bothriuridae): Overcoming Prey with Different Defensive Mechanisms

Scorpions are dominant predators in some environments. Nevertheless, most studies of predatory behavior in scorpions have focused on diet composition whereas some other relevant aspects, such as predatory strategy, have been poorly explored. Herein we evaluate the prey acceptance and predatory strategy of the scorpion Bothriurus bonariensis against sympatric prey with different defenses. As prey, we selected earwigs (Forficula cf. auricularia) which use pincer-like defensive appendages, hard-bodied isopods (Armadillium vulgare) known for their conglobation defensive strategy, soft bodied isopods (Porcellio cf. scaber), which secrete noxious substances as defense mechanisms, cockroaches with limited defensive mechanisms (Blatta cf. orientalis.) and spiders (Lycosa cf. poliostoma) which possess venomous fangs. Prey were offered to 21 adults of B. bonariensis in random order until all prey had been offered to all scorpions. Prey consumption and the number of attempts needed for capture were recorded. We also evaluated the effect of sting use on immobilization time as well as the prey capture strategies on the most consumed prey. We found that despite using a similar number of attempts for capturing all prey, spiders and armadillid isopods were less consumed than other prey. Immobilization times were longer for earwigs than for armadillid isopods and cockroaches. Scorpions used alternative predatory strategies against these aforementioned prey, although the stinger was used against all of them. These results show that scorpions are able to use different predatory strategies which might allow them to include prey with diverse defensive strategies in their diet.     

Asymmetric interactions in semiaquatic insects

Summary Interspecific interactions were studied in three coexisting species of predatory semiaquatic insects: Gyrinus substriatus Steph. (Coleoptera), Gerris lacustris (L.) and Gerris argentatus Schumm. (Hemiptera). Prey capture success was observed in trials with individuals of two different species. Two prey sizes were used: fruit flies Drosophila melanogaster and Mediterranean flour moths Ephetia kuehniella (Zeller). When the two species were starved for the same period of time, G. substriatus was generally more successful at catching prey than either Gerris species, independent of prey size. However, when individuals from the formerly dominant species of the pair were less hungry (i.e. fed shortly before trials), their prey capture success decreased. Prey sharing and prey stealing were observed in trials with large prey and occurred both intra- and interspecifically. The shift in dominance with differing hunger levels and the existence of prey sharing and prey stealing may make the interspecific competition more symmetric allowing these species to coexist.     

Characterization of restricted area searching behavior following consumption of prey and non-prey food in a cursorial spider, Hibana futilis

Cursorial spiders are important predators of crop pests in a variety of agricultural systems. Their survivorship, growth, and fecundity can be enhanced by the consumption of extra‐floral nectar. We recently showed that Hibana futilis (Banks) (Araneae: Anyphaenidae) engages in restricted area search following contact with nectar, is stimulated by nectar aroma, and can learn to recognize novel aroma cues. Studies have shown that H. futilis is also responsive to solvent extracts of the eggs and scales of the corn earworm, Helicoverpa zea Boddie (Lepidoptera: Noctuidae), one of its primary prey insects in cotton. The arrestment behavior of cursorial spiders following consumption of prey and non‐prey food has not been characterized. In the present study, the responses of spiders were measured following consumption of prey (H. zea eggs) or non‐prey (droplets of dilute honey) food items and compared with individuals tested without food items. The food items were presented to the spiders in test arenas constructed from the top of an inverted glass Petri dish cover. A combination of real time and recorded observations were made via a video camera attached to a computer. The behaviors and movement patterns of individual spiders were analyzed with behavioral tracking software. Significant differences in the behaviors and motion paths of spiders tested in the different treatments were observed. Hibana futilis displayed significantly more dispersal behavior on a blank test arena, than on test arenas supplied with honey droplets or moth eggs. Likewise, spiders tested on the blank arena crawled faster and their motion paths were significantly less tortuous than those of spiders tested in the arenas with honey or moth eggs. Following consumption of both the honey droplets and moth eggs, spiders showed elevated levels of restricted area search and lowered levels of dispersal behavior. The analysis showed that these spiders could crawl rapidly for extended distances. Behaviors such as restricted area search and learned recognition of food‐based stimuli would facilitate efficient location of the food resources needed to maintain their high activity levels.     

Trophic niche,capture efficiency and venom profiles of six sympatric ant‐eating spider species (Araneae: Zodariidae)

The arms race between specialist predators and their prey has resulted in the evolution of a variety of specific adaptations. In venomous predators, this can include venom composition, particularly if predators are specialized on dangerous prey. Here, we performed an integrative study using six species of highly specialized ant‐eating spiders of the genus Zodarion to investigate their phylogeny, realized trophic niche, efficacy in the capture of various ant species and venom composition. Data on natural diet obtained by next‐generation sequencing and field observations showed that the six Zodarion species exploit different ant species. Their phylogeny, based on mitochondrial and nuclear genes, correlated with the composition of their natural prey, indicating that closely related Zodarion species specialize on similar ant species. Prey‐capture parameters differed among Zodarion species suggesting prey‐specific efficacy. Similarly, the venom profiles of both low and high molecular compounds differed among species. Only the profiles of low molecular compounds were correlated with capture efficacy parameters, suggesting that the venom of Zodarion spiders contains prey‐specific components. Our study suggests that Iberian Zodarion spiders are specialized on particular ant species.     

Advantages of social foraging in crab spiders: Groups capture more and larger prey despite the absence of a web

Among group‐living spiders, subsocial representatives in the family of crab spiders (Thomisidae) are a special case, as they build protective communal leaf nests instead of extensive communal capture webs. It could thus be inferred that antipredator benefits (e.g., enhanced protection in larger nests) rather than foraging‐related advantages (e.g., capture of more and larger prey) promote sociality in this family. Nonetheless, subsocial crab spiders do share prey, and if this behaviour does not reflect mere food scramble but has a cooperative character, crab spiders may offer insights into the evolution of social foraging applicable to many other cooperative predators that hunt without traps. Here, we performed a comparative laboratory feeding experiment on three of the four subsocial crab spider species—Australomisidia ergandros, Australomisidia socialis and Xysticus bimaculatus—to determine if crab spiders derive advantages from foraging in groups. In particular, we tested artificially composed groups of five sibling spiderlings vs. single siblings in terms of prey capture success and prey size preference. Across species, groups had higher prey capture success (measured in terms of capture rates and capture latency) and were more likely to attack large, sharable prey—dynamics leading to reduced food competition among group members in favour of living and foraging in groups. Within groups, we further compared prey extraction efficiency among the three applied social foraging tactics: producing, scrounging and feeding alone. In A. ergandros, individuals were exceptionally efficient when using the non‐cooperative scrounger tactic, which entails feeding on the prey provided by others. Thus, our multispecies comparison confirms foraging advantages in maintaining a cooperative lifestyle for crab spiders, but also demonstrates the relevance of research into exploitation of cooperative foraging in this family.     

Do the Color and Pattern of <Emphasis Type="Italic">Micrathena gracilis</Emphasis> (Araneae: Araneidae) Attract Prey? Examination of the Prey Attraction Hypothesis and Crypsis

Recent studies have provided evidence that spiders’ color and pattern may attract prey items to their webs, thus increasing their foraging success. However, these studies were conducted on tropical spiders, and no studies have examined this phenomenon in temperate spiders. We examined the role of color and pattern in a North American spiny orb-weaver, Micrathena gracilis. We found that prey capture rates were similar between webs that contain spiders and webs in which spiders were removed. Additionally, we found a trend that painted spiders captured more prey than unpainted spiders. Although our results were not statistically significant, they contradict previous studies examining the role of color in prey attraction.     

Conspicuous colouration attracts prey to a stationary predator

Abstract 1. Conspicuous body colouration is counter‐intuitive in stationary predators because sit‐and‐wait tactics frequently rely on concealed traps to capture prey. Consequently, bright colours and contrasting patterns should be rare in predators using traps as they may alert potential prey. Yet, some orb‐weaving spiders are brightly coloured and contrastingly patterned. How can conspicuousness of trap‐building sit‐and‐wait predators be favoured by natural selection? 2. Observations of spiny spiders Gasteracantha fornicata in north‐eastern Australia showed that the size of spiders relative to their orb webs correlated positively with relative prey numbers already captured in their webs. A possible explanation is that the relatively larger appearance of the yellow–black striped dorsal surface of this spider attracts more visually oriented prey items. Prey attracted to webs may get trapped, thereby increasing the spiders' foraging success. 3. To test this hypothesis for the function of conspicuous body colouration, a field experiment was conducted that documented the prey capture rates of spiny spiders after manipulating or sham‐manipulating their appearance. 4. As predicted, spiders that were dyed black on their striped dorsal surface caught relatively fewer prey items than did control spiders. Thus, conspicuous dorsal body colouration may be adaptive in spiny spiders because it increases foraging success and, presumably, survival rates and reproductive outputs. Overall, these data support the colour‐as‐prey‐attractant hypothesis in a stationary, trap‐building predator.     

Predation in a temporary pond with special attention to the trophic role of Triops cancriformis (Crustacea: Branchiopoda: Notostraca)

Temporary ponds are described as environments with a low predation pressure. Notostracans inhabit these types of ponds, and some populations acquire a high proportion of larger individuals, whose feeding behaviour is mainly predatory. The predation nature of Triops cancriformis is not widely accepted, because its diet is still partly controversial. We analysed the diet of one population of T. cancriformis in a Mediterranean temporary pond (Espolla pond, NE Iberian peninsula) to evaluate its predation behaviour. The gut content of the individuals bigger than 10 mm is mainly composed of detritus, plant fibres and microcrustaceans (cladocerans, ostracods and copepods). The prey number increases with the body size of individual T. cancriformis as previously described. Sex-biased predation was observed for one copepod prey, but not for the other. Predation pressure in that community was monitored along six hydroperiods as the percentage of predator biomass (not only T. cancriformis) in relation to the non-predator biomass. The proportion of predator biomass is high, and this contrasts with the low predation pressure expected for a temporary system with short hydroperiods.     

Capture efficiency and trophic adaptations of a specialist and generalist predator: A comparison

Specialist true predators are expected to exhibit higher capture efficiencies for the capture of larger and dangerous prey than generalist predators due to their possession of specialized morphological and behavioral adaptations. We used an araneophagous spider (Lampona murina) and a generalist spider (Drassodes lapidosus) as phylogenetically related model species and investigated their realized and fundamental trophic niches and their efficacy with respect to prey capture and prey handling. The trophic niche of both species confirmed that Lampona had a narrow trophic niche with a predominance of spider prey (including conspecifics), while the niche of Drassodes was wide, without any preference. DNA analysis of the gut contents of Lampona spiders collected in the field revealed that spiders form a significant part of its natural diet. Lampona captured significantly larger prey than itself and the prey captured by Drassodes. As concerns hunting strategy, Lampona grasped the prey with two pairs of legs possessing scopulae, whereas Drassodes immobilized prey with silk. Lampona possess forelegs equipped with scopulae and a thicker cuticle similar to other nonrelated araneophagous spiders. Lampona fed for a longer time and extracted more nutrients than Drassodes. We show that specialized behavioral and morphological adaptations altogether increase the hunting efficiency of specialists when compared to generalists.     

Foraging advantages of mixed-species association between solitary and colonial orb-weaving spiders

This study investigated association between solitary orb-weaving spiders and a colonial orb-weaving spider, Metepeira incrassata (Araneae: Araneidae). Spiders were sampled along transects and an index of species association showed that two of the species were associated more frequently than expected based on a null hipothesis of random co-occurrence. The potential advantages of mixed-species association were investigated by comparing prey-capture success of one of these associates, Nephila clavipes (Araneae: Tetragnathidae), when it occurs alone, in single-species groups, and when associated with M. incrassata colonies. Field observations of prey-capture success by all three of these categories of N. clavipes revealed that individuals in M. incrassata colonies captured significantly more prey than solitaries or individuals in single-species groups. The increase in prey capture by N. clavipes in M. incrassata colonies may result from utilization of a foraging niche which intercepts a diffirent spectrum of prey than that available to single-species groups or solitaries. Related to this enhanced prey consumption is greater fecundity of spiders in association with M. incrassata as compared to solitaries or individuals in single-species groups.     

Experimental assessment of trophic ecology in a generalist spider predator: Implications for biocontrol in Uruguayan crops

Conservative biological control promotes the use of native natural enemies to limit the size and growth of pest populations. Although spiders constitute one of the most important groups of native predators in several crops, their trophic ecology remains largely unknown, especially for several generalist taxa. In laboratory, we assessed the predatory behaviour of a wandering spider (the wolf spider Lycosa thorelli (Keyserling, 1877) against several arthropods varying in size and trophic positions, all found in South American soybean and rice crops. As prey we used the bug Piezodorus guildinii (Westwood, 1837) as well as larvae and adults of the moth Spodoptera frugiperda (Smith, 1797), both being considered important pests in Uruguayan crops. We also used several non-pest arthropods as prey, sarcophagid flies, carabid beetles and wolf spiders. All prey were attacked in more or less high, although not statistically differing, proportions. However, carabids were not consumed, and bugs were consumed in significantly lower proportions than flies. A negative correlation was found between prey size and acceptance rate. Immobilization times were longer against larvae when compared to moths and flies, while predatory sequences were longer for bugs when compared to flies, moths and spiders. In addition, we found a positive effect of prey size on predatory sequence length and complexity. Our results confirm the ability of spiders to attack and feed upon prey with different morphologies, included well-defended arthropods, and their potential use as natural enemies of several pests in South American crops.     

Distinct feeding strategies of generalist and specialist spiders

1. Feeding behaviour of generalist and specialist predators is determined by a variety of trophic adaptations. Specialised prey‐capture adaptations allow specialists to catch relatively large prey on a regular basis. As a result, specialists might be adapted to exploit each item of prey more thoroughly than do generalists. 2. It was expected that obligatory specialist cursorial spiders would feed less frequently than generalists but for a longer time and, thus, that their foraging pause would be longer. First, the feeding frequencies of three generalist spider species (Cybaeodamus taim, Harpactea hombergi, Hersiliola sternbergsi) were compared with those three phylogenetically related specialist species: myrmecophagous Zodarion rubidum, and araneophagous Nops aff. variabilis and Palpimanus orientalis. 3. Generalists captured more prey, exploited each item of prey for a significantly shorter time, and had a shorter foraging pause than was the case for specialists. Generalists also gained significantly less relative amount of prey mass than did specialists. 4. Second, the study compared the prey DNA degradation rate in the gut of generalists and specialists by means of PCR. The degradation rate was not significantly different between specialists and generalists: the detectability half‐life was estimated to exist for 14.3 days after feeding. 5. This study shows that the feeding strategies of cursorial generalist and obligatory specialist spiders are different. Obligatory specialists have evolved a feeding strategy that is based on thorough exploitation of a few large prey, whereas generalists have evolved a strategy that is based on short exploitation of multiple small items of prey.     

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.