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Lepidoptera is one of the most diverse orders of insects, their larvae are very abundant in many habitats, and frequent prey of various predators. To decrease predation risk, caterpillars developed several means of defence, among them timing their activity to avoid predators (seeking enemy-free time). Although the enemy-free time hypothesis is often invoked to explain caterpillar behaviour, empirical evidence for it is scarce. We tested whether such enemy-free time exists in a temperate forest by comparing predation pressure on artificial caterpillars during day and night on the ground in forest fragments in Denmark. We found a high predation rate, 23.9%d-1, and higher predation rate at night (30.9%d-0.5) than during the day (17.0%d-0.5), both by invertebrate (23.3%d-0.5 vs. 12.4%d-0.5) and vertebrate (8.5%d-0.5 vs. 3.3%d-0.5) predators. The most important predators were chewing insects (73.4% of all attacks) and small mammals (19.0%). Attack rates on red caterpillars were higher (30.0%d-1) than on green ones (19.5%d-1). Overall, these data do not support the idea that night activity can provide enemy-free time for solitary caterpillars on the temperate forest floor. [ABSTRACT FROM AUTHOR]

The effect of viewing distance on the perception of visual texture is well known: spatial frequencies higher than the resolution limit of an observer's visual system will be summed and perceived as a single combined colour. In animal defensive colour patterns, distance-dependent pattern blending may allow aposematic patterns, salient at close range, to match the background to distant observers. Indeed, recent research has indicated that reducing the distance from which a salient signal can be detected can increase survival over camouflage or conspicuous aposematism alone. We investigated whether the spatial frequency of conspicuous and cryptically coloured stripes affects the rate of avian predation. Our results are consistent with pattern blending acting to camouflage salient aposematic signals effectively at a distance. Experiments into the relative rate of avian predation on edible model caterpillars found that increasing spatial frequency (thinner stripes) increased survival. Similarly, visual modelling of avian predators showed that pattern blending increased the similarity between caterpillar and background. These results show how a colour pattern can be tuned to reveal or conceal different information at different distances, and produce tangible survival benefits. [ABSTRACT FROM AUTHOR]

Many animals show conspicuous colour patterns that inform potential predators about their unprofitability due to their toxicity or unpalatability (aposematism). However, no systematic work has evaluated the colouration of crabs in terms of aposematism, even though many species exhibit conspicuous colouration. We conducted a laboratory study to compare predation risk from a fish predator, the barred mudskipper (Periophthalmus argentilineatus), in two sympatric fiddler crab species with different body colour patterns: Austruca perplexa with brownish-white colourations and Paraleptuca crassipes with red-and-black colour patterns. Fiddler crabs and mudskippers are active on tidal flats during low tides. A predation trial by stocking one crab and one mudskipper in a test arena was repeated five times for each species–sex combination. The animal behaviour was video recorded for 24 h, and crabs were confirmed to be alive or dead after 72 h. A. perplexa females were most vulnerable to predation from mudskippers. The attack intensity from mudskippers was stronger during the nighttime than daytime against P. crassipes females and males and A. perplexa males, suggesting that mudskippers may avoid them by visually detecting the body colouration in P. crassipes and the body structure in males of both species (i.e. a large weaponry claw) during the daytime. Mudskippers eventually preyed on and consumed some individuals in both species–sexes. Mudskippers are known to shift their main food components from small crustaceans through polychaete worms to crabs, such as fiddler crabs, and unpalatable polychaete worms tend to be brightly coloured. We suggest that the red colouration of P. crassipes may be incidental mimicry of the unpalatable red/orange-coloured polychaete worms that mudskippers might have learned to avoid. • We compared predation risk from mudskippers in fiddler crabs with different colours. • We employed brownish-white–coloured species and red-coloured species. • Females of brownish-white–coloured species were most vulnerable to predation. • Mudskippers avoided red-coloured species and males of both species. [ABSTRACT FROM AUTHOR]