1. Selection imposed by visually hunting predators has driven the evolution of colour-based antipredator defence strategies such as crypsis, masquerade, mimicry and aposematism. Individuals of many animals are generally considered to rely on a single type of defence strategy, but individuals of some species use multiple colour-based defences. Many animals switch between colour-based defences against visually hunting predators during ontogeny. However, why this occurs remains poorly understood.2. The crab spider Phrynarachne ceylonica is an often-cited example of a bird dropping masquerade. It has recently been demonstrated that P. ceylonica crab spiders gain protection from their predators by being misidentified as bird droppings by their predators. P. ceylonica females show an ontogenetic shift in colour defences: early instars possess a dark and cryptic form, while at later instars and as adults, the spiders resemble bird droppings. We hypothesised that this shift may be driven by differential changes in predation risk of two defence strategies with increasing body size due to ontogeny. We tested this hypothesis by presenting naïve domestic chicks with 3Dprinted artificial spiders of two different sizes (small, large) and two colours (dark, bird dropping-like), and determined whether larger bird dropping-like spiders are more readily found and attacked than cryptic forms by chicks.We found that small cryptic spiders were more difficult to detect than small bird dropping masquerading spiders, but large cryptic spiders were attacked much more quickly and more frequently than large bird dropping masquerading spiders.4. Increasing predation pressure on larger, cryptic spiders during ontogeny suggests that switching to bird dropping masquerade may be a more effective defence as spiders increase in size. We thus conclude that the ontogenetic shift from crypsis to masquerade is adaptive.

Animals may consider both biotic and abiotic factors in foraging site choice. Among the biotic factors, food availability and predation risk are two widely reported important factors in determining foraging site fidelity. Their earlier investments, such as those retreat-building species' efforts in retreats construction, however, have been largely ignored. The orb-web spider Cyclosa monticola constructs a long column of masquerading detritus decoration in its web for predator avoidance purpose. This detritus decoration also functions as a retreat. However, the role of the detritus decoration for its foraging site fidelity is unknown. By manipulating three factors, presence of detritus decoration, prey availability and predation risk to the spider webs in the field, we show that the self-constructed detritus decoration is as important as prey availability and predation risk in mediating foraging site fidelity. In addition, the web area also has a significant impact to the foraging site fidelity of the spider, those with larger webs were more likely to leave after being manipulated. However, other factors such as spider body size, decoration length and rain all have no significant impact. Our study may strengthen the current understanding of the movement and foraging of animals, especially those building retreats.

When sexual conflict selects for reproductive strategies that only benefit one of the sexes, evolutionary arms races may ensue. Female sexual cannibalism is an extreme manifestation of sexual conflict. Here we test two male mating strategies aiming at countering sexual cannibalism in spiders. The “better charged palp” hypothesis predicts male selected use of the paired sexual organ (palp) containing more sperm for their first copulation. The “fast sperm transfer” hypothesis predicts accelerated insemination when cannibalism is high. Our comparative tests on five orbweb spider species with varying levels of female sexual cannibalism and sexual size dimorphism (SSD) reveal that males choose the palp with more sperm for the first copulation with cannibalistic females and that males transfer significantly more sperm if females are cannibalistic or when SSD is biased. By supporting the two hypotheses, these results provide credibility for male mating syndrome. They, however, open new questions, namely, how does a male differentiate sperm quantities between his palps? How does he perform palp choice after assessing his cannibalistic partner? By conducting follow-up experiments on Nephilengys malabarensis, we reveal that it is sperm volume detection, rather than left-right palp dominance, that plays prominently in male palp choice.

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