Vampire spiders reveal their killing secrets
15 June 2012
UC researchers are sinking their teeth into the picky eating habits of blood-gorging vampire jumping spiders.
New research by Dr Ximena Nelson and Professor Robert Jackson (Biological Sciences), published this month in The Journal of Experimental Biology, has found Evarcha culicivora jumping spiders, also known as vampire spiders, are selective eaters who are able to identify their preferred prey by their antennae.
Dr Nelson, a lecturer in animal behaviour in the School of Biological Sciences, said the Kenyan arachnid lives in an environment that is swamped with insects yet its preferred delicacy was female blood-fed Anopheles mosquitoes. This raised the intriguing question of how the spider spotted its prey among all the other similarly sized insects infesting the area.
Using a combination of “Frankenstein mosquitoes” and animated simulations, Dr Nelson and Professor Jackson were able to determine the mosquito features the vampire spider fixated on.
“Obviously, blood-fed females have an engorged red abdomen and the other difference that comes to mind between males and females is the antennae,” said Dr Nelson.
Male Anopheles have luxuriant fluffy antennae while the female's are less elaborate, she said.
Using the body parts of dead male and female mosquitoes, Dr Nelson and Professor Jackson’s research team created a range of hybrid mosquitoes – combining the head and thorax of one insect with the abdomen of another – to test the jumping spider’s preferences. Animated simulations of blood-engorged mosquitoes with male or female antennae were also offered to the spider.
Dr Nelson said it was clear the spider’s preference was for blood-engorged females, even when presented with females engorged with transparent sugar solution. And, when the spiders were offered the choice between a Frankenstein female (made from the head and thorax of one female fused to the blood-engorged abdomen of a second female) and a hybrid constructed from a male head-and-thorax and a blood-engorged female abdomen, the spiders usually selected the hybrid with the female antennae, even though both hybrids were packed with blood. Also, when she tempted the spiders with animated simulations of blood-engorged mosquitoes with either male or female antennae, the spiders consistently pounced on the simulated female.
Dr Nelson said the spiders weren't just picking out Anopheles mosquitoes with abdomens full of blood – they were able to identify the mosquitoes by their antennae.
“The thing that really amazed me is that I couldn't actually see the difference when I was looking at the screen,” said Dr Nelson, who said the mosquitoes were too small for her to discern the insects' minute antennae even when she got down to the spider’s level.
Having found that picky E. culicivora can identify the tastiest mosquitoes by their antennae, Dr Nelson is now keen to find out how they process this visual information – whether they assess all of the mosquito's characteristics simultaneously or systematically tick features off a check list before deciding to attack.
The full paper, titled The discerning predator: decision rules underlying prey classification by a mosquito-eating jumping spider, can be found at http://jeb.biologists.org.
For more information please contact:
Dr Ximena Nelson
Lecturer in Animal Behaviour
School of Biological Sciences
University of Canterbury
Ph: +64 3 364-2987 ext 4050