Spider Feeding Habits
Evarcha culicivora is a species of jumping spider from Kenya. It is also known as the "Vampire Spider." It is the only known animal that selects its prey based on what the latter has eaten. This species selects blood-filled mosquitoes more often than unfed ones. How could these picky spiders pick out blood-engorged Anopheles mosquitoes from the swarms of similarly sized insects infesting the area? In new research it was identified that Anopheles mosquitoes (males and females) is quite straightforward. "The bodies of Anopheles mosquitoes rest on a 45 degree angle from the substrate but most others rest parallel", the authors explains. But what other distinguishing features could the famished spiders use when selecting the females specifically? "Obviously, blood-fed females have an engorged red abdomen and the other difference that comes to mind between males and females is the antennae". The research studies the spider's psychology in selecting which mosquito to then dine on.
The study was published in The Journal of Experimental Biology.
Collecting male and female Anopheles and Culex mosquitoes at the International Center for Insect Physiology and Ecology in Kenya, the researchers constructed hybrid mosquitoes. Combining the head and thorax of one insect with the abdomen of another, the team was able to produce Frankenstein mosquitoes with blood-engorged female abdomens and male antennae, slender male abdomens and female antennae, and every other combination in between. Then, they mounted the hybrid mosquitoes in their correct postures and tested the spiders' preferences.
"The great thing about jumping spiders is they're very decisive", recalls Nelson one of the authors, who could clearly see that the spiders preferred intact blood-engorged females over everything else, even females engorged with transparent sugar solution. And, when Nelson offered the spiders 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. When she then tempted the spiders with animated simulations of blood-engorged mosquitoes with either male or female antennae, the spiders consistently pounced on the simulated female.
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", recalls Nelson. Even when she got down to the spider's level, the mosquitoes were too small for Nelson to discern the insects' minute antennae.
Having found that picky E. culicivora can identify the tastiest mosquitoes by their antennae, Nelson is curious next to find out how they process this visual information. After all their brains are mighty small.
The article can be found at Jumping Spiders,
Spider image via Wikipedia.