Masquerading predators deceive prey by aggressively mimicking bird droppings in a crab spider

In aggressive mimicry, a predator accesses prey by mimicking the appearance and/or behavior of a harmless or beneficial model in order to avoid being correctly identified by its prey. The crab spider genus Phrynarachne is often cited as a textbook example of masquerading as bird droppings in order to avoid predation. However, Phrynarachne spiders may also aggressively mimic bird droppings in order to deceive potential prey. To date, there is no experimental evidence to support aggressive mimicry in masquerading crab spiders, therefore, we performed a field survey, a manipulative field experiment, and visual modeling to test this hypothesis using Phrynarachne ceylonica. We compared prey-attraction rates among bird droppings, spiders, and control empty leaves in the field. We found that although all prey combined and agromyzid dipterans in particular were attracted to bird droppings at a higher rate than to spiders, other dipterans and hymenopterans were attracted to bird droppings at a similar rate as spiders. Both spiders and bird droppings attracted insects at a significantly higher rate than did control leaves. As predicted, prey were attracted to experimentally blackened or whitened spiders significantly less frequently than to unmanipulated spiders. Finally, visual modeling suggested that spiders and bird droppings can be detected by dipterans and hymenopterans against background leaves, but they are indistinguishable from each other. Taken together, our results suggest that insects lured by spiders may misidentify them as bird droppings, and bird dropping masquerading may serve as aggressive mimicry in addition to predator avoidance in P. ceylonica.

Captivating color: evidence for optimal stimulus design in a polymorphic prey lure

Araneid spiders use abstract color patterns to attract prey. The chromatic properties of these displays vary extensively, both within and across species, and they are frequently polymorphic. Variation is often expressed in terms of signal hue (color per se), but it is unclear precisely how attractiveness scales with this property. We assessed captures among color-manipulated females of the dimorphic jeweled spider Gasteracantha fornicata in their natural webs. The manipulation magnified the natural variation in stimulus hue independently of chroma (saturation) across a range spanning most of the color spectrum. Catch rate varied across treatments in simple accordance with how greatly stimulus hue deviated from either of the two extant phenotypes. Predictions based upon fly-perceived background contrast were unsupported despite dipterans constituting ~60 % of prey. This study isolates the importance of stimulus hue and supports the premise that extant phenotypes reside in an optimal spectral range for prey attraction.

Color lures in orb-weaving spiders: a meta-analysis

Lures are deceptive strategies that exploit sensory biases in prey, usually mimicking a prey’s mate or food item. Several predators exploit plant–pollinator systems, where visual signals are an essential part of interspecific interactions. Many diurnal, and even nocturnal, orb-web spiders present conspicuous body coloration or bright color patches. These bright colors are regarded as color-based lures that exploit biases present in insect visual systems, possibly mimicking flower colors. The prey attraction hypothesis was proposed more than 20 years ago to explain orb-web spider coloration. Although most data gathered so far has corroborated the predictions of the prey attraction hypothesis, there are several studies that refute these predictions. We conducted a multilevel phylogenetic meta-analysis to assess the magnitude of the effect of conspicuous orb-web spider body coloration on prey attraction. We found a positive effect in favor of the prey attraction hypothesis; however, there was substantial heterogeneity between studies. Experimental designs comparing conspicuous spiders to painted spiders or empty webs did not explain between-studies heterogeneity. The lack of theoretical explanation behind the prey attraction hypothesis makes it challenging to address which components influence prey attraction. Future studies could evaluate whether color is part of a multicomponent signal and test alternative hypotheses for the evolution of spider colors, such as predator avoidance and thermoregulation.

Distribution of native European spiders follows the prey attraction pattern of introduced carnivorous pitcher plants

Carnivorous plants and spiders are known to compete for resources. In North America, spiders of the genus Agelenopsis are known to build funnel-webs, using Sarracenia purpurea pitchers as a base, retreat and storage room. They also very likely profit from the insect attraction of S. purpurea. In a fen in Europe, S. purpurea was introduced ~65 years ago and co-occurs with native insect predators. Despite the absence of common evolutionary history, we observed native funnels-spiders (genus Agelena) building funnel webs on top of S. purpurea in similar ways as Agelelopsis. Furthermore, we observed specimen of the raft-spider (Dolmedes fimbriatus) and the pygmy-shrew (Sorex minutus) stealing prey-items out of the pitchers. We conducted an observational study, comparing plots with and without S. purpurea, to test if Agelena were attracted by S. purpurea, and found that their presence indeed increases Agelena abundance. Additionally, we tested if this facilitation was due to the structure provided for building webs or enhanced prey availability. Since the number of webs matched the temporal pattern of insect attraction by the plant, we conclude that the gain in food is likely the key factor for web installation. Our results provide an interesting case of facilitation by an introduced plant for a local predator, which has developed in a very short time scale.

Attraction of prey

The ability to attract prey has long been considered a universal trait of carnivorous plants. We review studies from the past 25 years that have investigated the mechanisms by which carnivorous plants attract prey to their traps. Potential attractants include nectar, visual, olfactory, and acoustic cues. Each of these has been well documented to be effective in various species, but prey attraction is not ubiquitous among carnivorous plants. Directions for future research, especially in native habitats in the field, include: the qualitative and quantitative analysis of visual cues, volatiles, and nectar; temporal changes in attractants; synergistic action of combinations of attractants; the cost of attractants; and responses to putative attractants in electroantennograms and insect behavioral tests.

Artificial night light alters nocturnal prey interception outcomes for morphologically variable spiders

Artificial night light has the potential to significantly alter visually-dependent species interactions. However, examples of disruptions of species interactions through changes in light remain rare and how artificial night light may alter predator–prey relationships are particularly understudied. In this study, we examined whether artificial night light could impact prey attraction and interception inNephila pilipesorb weaver spiders, conspicuous predators who make use of yellow color patterns to mimic floral resources and attract prey to their webs. We measured moth prey attraction and interception responses to treatments where we experimentally manipulated the color/contrast of spider individuals in the field (removed yellow markings) and also set up light manipulations. We found that lit webs had lower rates of moth interception than unlit webs. Spider color, however, had no clear impact on moth interception or attraction rates in lit nor unlit webs. The results show that night light can reduce prey interception for spiders. Additionally, this study highlights how environmental and morphological variation can complicate simple predictions of ecological light pollution’s disruption of species interactions.

Biología de las plantas carnívoras: aspectos ecológicos y evolutivos

Carnivorous plants have the ability for attracting, catching, digesting and assimilating preys, through morphological and physiological specializations of theirs leaves. In this work we review some poorly studied aspects regarding the ecology of carnivorous plants, as well as, the selective pressures that have shaped the characteristic attributes of these plants. In particular, we emphasize those aspects related with the mechanisms of prey attraction, the selective value of capture, the existence of a trade-off between capture and pollination evolution, and the role of selective constraints on the evolution of the carnivorous habit.

Jewelled spiders manipulate colour-lure geometry to deceive prey

Selection is expected to favour the evolution of efficacy in visual communication. This extends to deceptive systems, and predicts functional links between the structure of visual signals and their behavioural presentation. Work to date has primarily focused on colour, however, thereby understating the multicomponent nature of visual signals. Here I examined the relationship between signal structure, presentation behaviour, and efficacy in the context of colour-based prey luring. I used the polymorphic orb-web spider Gasteracantha fornicata , whose yellow- or white-and-black striped dorsal colours have been broadly implicated in prey attraction. In a manipulative assay, I found that spiders actively control the orientation of their conspicuous banded signals in the web, with a distinct preference for near-diagonal bearings. Further field-based study identified a predictive relationship between pattern orientation and prey interception rates, with a local maximum at the spiders' preferred orientation. There were no morph-specific effects on capture success, either singularly or via an interaction with pattern orientation. These results reveal a dynamic element in a traditionally ‘static’ signalling context, and imply differential functions for chromatic and geometric signal components across visual contexts. More broadly, they underscore how multicomponent signal designs and display behaviours may coevolve to enhance efficacy in visual deception.