Jumping vampire spiders pick their prey by antennae
Vampire spiders, like their mythological namesakes, always go for the blood.
Evarcha culicivora, or jumping vampire spiders, tend to be picky eaters. They're found in Kenya in environments teaming with insects, and they usually feast on mosquitoes. But they don't settle for just any bug.
Ximena Nelson and Robert Jackson, from the University of Canterbury, New Zealand, studied the arachnid's eating habits and found that the spiders are extremely selective. They feed indirectly, so they can't get nutrients from male mosquitoes, who do not drink blood.
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The prey they prize most are female mosquitoes who have recently fed on blood, but the researchers wanted to know just how they select that specific supper from swarms of mosquitoes that look the same to the average person.
"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 Nelson. Male Anopheles mosquitoes have fluffy antennae, while female's are less elaborate.
In order to see which feature the spiders use to separate the females from the crowd, Nelson and Jackson created 'Frankenstein' mosquitoes by mixing the insects body parts - female abdomens with male antennae, male abdomens with female antennae, and every other combination possible.
They found that when they served these hybrid mosquitoes to the spiders, the clear favorite was the intact blood-engorged female corpse, which means blood is indeed a factor when selecting prey.
But when Nelson offered the spiders a choice between a Frankenstein female (the head and thorax of one female fused to the blood-engorged abdomen of another female) and a hybrid with male antennae on a female abdomen, the spiders usually chose the hybrid with female antennae.
"The thing that really amazed me is that I couldn't actually see the difference [in antennae] when I was looking at the screen", Nelson said. But the spiders could, and they based their feeding decisions on the look of the antennae.
"In the past it was thought that jumping spiders responded to very basic stimuli that triggered predatory behavior. Something along the lines of, 'It is small and it moves, therefore it is prey,'" Nelson told LiveScience. This new study, published in the Journal of Experimental Biology, shows that it's not quite that simple.
"It is clear from these results that this type of 'algorithm' is not used by E. culicivora [the jumping spider]. At the very least, it is much more sophisticated," Nelson said.
Nelson now wants to test whether the spiders take in all prey characteristics simultaneously, or if they tick of a checklist before deciding to pounce.
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