Biological mimicry is widespread in nature. Many poisonous or otherwise unpalatable organisms display warning signs, such as black and yellow or black and red stripes, to deter would-be predators. Batesian mimicry to refers to non-poisonous organisms which closely resemble poisonous ones. (This phenomenon is named after Walter Henry Bates, who first proposed it in 1862.) Some organisms, such as the stick insect, are camouflaged, while others behave in deceptive ways when approached by a predator.
Some organisms are known to lure prey by mimicking them, but the converse situation, in which prey mimics its predator, is very rare. In the first edition of the new online open access journal PLoS One, Rota and Wagner show that metalmark moths have wing markings which resemble the markings on jumping spiders. The moth also behaves in such a way as to enhance its resemblance of the spider. When perched on leaves, they adopt a particular posture, with their hindwings fanned out and brought forward, and positioned perpendicular to the forewings. In this position, the white markings closely resemble those found on the jumping spider:
Rota and Wagner carried out trials in which jumping spiders were presented with metalmark moths and other types of moths which do not display wing markings. The metalmarks had far higher survival rates than the other moths: 5 out of 69 were caught by the spiders, compared to 43 out of 69 of the other moths.
The resemblance between the moth and the spider is quite astonishing. Although the jumping spider’s sense of vision is among the most acute of all the arthropods, it is not good enough to distinguish between the metalmark and another spider – the spiders were often observed performing territorial displays when they encountered the metalmarks, providing further evidence that they mistook the moths for other jumping spiders:
The wing markings of the metalmark may also confer another advantage. Because the spiders move extremely quickly, they often evade capture by birds swooping down on them from above. Rota and Wagner suggest that the markings may also fool birds into thinking that metalmarks are jumping spiders; if this is the case, birds might be less likely to attempt to capture the moths. A review by the authors of the wing markings of other insects suggests that mimicry of jumping spiders may be more widespread than was previously thought.