Spider's use of smell nothing to sniff at

A tiny East African jumping spider has proven to University of Canterbury researchers that it uses more than just its eight eyes to hunt prey and find a mate.



Dr Fiona Cross and Professor Robert Jackson (Biological Sciences) have found that the mosquito-eating spider, Evarcha culicivora, uses olfactory search images when looking for its next meal or a mate.



Professor Jackson said search images, also known to cognitive psychologists as selective attention, are relevant when an animal becomes prepared to detect and identify something specific.



He said most studies in this area are based on vision rather than olfaction.



Dr Cross said while it was known that Evarcha culicivora used odour to track mates and blood-carrying mosquitoes, its use of olfactory search images had not been investigated before.



“There have been a couple of olfactory search image studies carried out on skunks and sniffer dogs but those experiments did not do the same things we did. While the skunk and sniffer dog tests looked at what happened when the animals learned a specific odour over an extended period of time, we compared what happens when the odour is conspicuous and when it’s masked by other odours.



“We only found evidence of olfactory search images when the odour was difficult to find, which suggests that the spiders were using selective attention rather than just showing a preference for that odour. The spiders could even do this after only one prior encounter with a particular odour source, which suggests that the search images they called up were innate and not acquired by perceptual learning.



“Jumping spiders are known to have good eyesight for animals of their size, but the results of our experiment suggest that they also make strong use of olfaction.”



Dr Cross and Professor Jackson’s findings, based on research conducted in Kenya, have been published online in the Proceedings of the Royal Society of London (Series B) with the title “Olfactory search image use by a mosquito-eating predator”.



Dr Cross studied Evarcha culicivora for both her masters and PhD, looking at mate choice behaviour and on their use of vision to detect prey and mates. Her current research is being supported by a three-year Foundation for Research, Science and Technology Postdoctoral Fellowship, which she received in February this year.



“With the fellowship I hope to look at the spider’s use of olfactory search images in more detail and find out what exactly is in the odour that the spiders are paying attention to by looking at the chemical make-up of the spiders themselves and the mosquitoes it eats.



“The other thing I’m intrigued by is how, when the spiders feed on blood, they become more attractive to the opposite sex — it’s like they pick up some kind of blood perfume — so I want to look more closely at that as well.”