Ant-mimicry in reverse by a colourful jumping spider from South-East Asia

Christina Painting *1, Matthew Bulbert 2, Gwendolyn Chow 3, Y Norma-Rashid 4, Daiqin Li 3

1 University of Auckland, Auckland, New Zealand
2 Macquarie University, NSW, Australia
3 National University of Singapore, Singapore
4 University of Malaya, Kuala Lumpur, Malaysia

Batesian mimics avoid predators by imitating visual, acoustic or chemical signals of a dangerous or unpalatable prey species. Ants are a particularly common model for mimics to resemble. Many predators have a strong aversion to ants because they have an arsenal of defences such as being able to sting, bite or spray acid. Orsima ichneumon is a jumping spider from South-East Asia that has been proposed to be an ant-mimic in reverse. They have elongated spinnerets that resemble insect antennae and mouthparts, and strong abdominal constrictions which gives the appearance of an ant’s head and thorax. However, O. ichneumon are spectacularly coloured, leading researchers to question their likelihood as ant-mimics. We hypothesised that despite their bright colouration, O. ichneumon avoid predation using ant-like shape and movement. We conducted experiments using an ant-averse, spider-eating predator (Portia labiata) and compared the probability and time to attack between O. ichneumon, a closely related typical jumping spider (Cosmophasis umbratica), and an ant (Camponotus auriventris) found in association with O. ichneumon. We found a gradient in the probability of attack, with the typical jumping spider attacked most frequently, followed by O. ichneumon, and the ant attacked least often. Portia labiata also took longer to decide whether to attack when presented with O. ichneumon, compared to the typical jumping spider or the ant. A comparison of outline shape using Fourier analysis also revealed that O. ichneumon resembles an ant when considered in reverse, but in normal orientation looks like a jumping spider. Our results suggest that imperfect ant mimicry confuses predators and allows O. ichneumon time to escape.

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