Saturday, October 29, 2005

Secondhand Vampire Spiders!

` Dory pointed this article out to me from Very strange indeed... it's about an East African jumping spider, studied by Ximena Nelson...

The spider, Evarcha culicivora, lacks the ability to pierce skin and to sip blood, so instead it feeds indirectly on blood by choosing, as its preferred meal, female mosquitoes that have just engorged themselves with a victim's blood.

The blood-hungry spider is the first predator ever identified that selects its prey based upon what the prey just ate. Similar to a protein shake, blood can be a highly nutritious drink that goes down smoothly.

` A spider that feeds on second-hand blood! It can consistently tell a blood-filled female mosquito apart from other mosquitoes by both its sense of smell alone and by sight alone.
` It can accurately pick out a blood-fed mosquito and pursue only that one!
` So, why not crawl onto prey and get blood directly? One reason is that it could get swatted before it could crawl away (and I guess this would make sense since they can't fly like mosquitos can). Also, their mouthparts are held close to the face, instead of pointing forwards as in mosquitos. If they should stab themselves, accidentally, they could die.
` (It is easy to see how the primarily nectar-feeding mosquitoes could have evolved to feed on blood - they had sucking mouthparts to begin with.)
` Really, I guess it makes sense that they don't go to the source of blood, as jumping spiders are made to pounce on small insects. This species merely singles out the ones that are full of blood, and Africa is a hotspot for those.
` The article concludes:

Steve Heydon, senior scientist and collection manager for the Bohart Museum of Entomology at the University of California at Davis, was surprised to hear of the discovery.

"I know of parasitic wasps that find their caterpillar prey based on the smell of the caterpillar's feces, but I'd never heard of a spider like this before," Heydon told Discovery News. "Spiders don't have much sense of smell, so that part of the study is especially surprising."

Heydon agrees with Nelson that spiders now probably lack the right body parts and structure to evolve into direct bloodsuckers, but he does not completely rule this out for the distant future.

"Maybe spiders will end up like bed bugs," he said. "They could have that bed-bug lifestyle of laying around and coming out at night when a big, huge, monstrous food item comes tantalizingly near them and simply goes to sleep."

` In other words, this is a possible way that a jumping spider could evolve into a parasite by graduating from secondhand blood in mosquitoes to fresh blood in large vertebrates, which was just what I had been thinking.


Aaron said...

Well, I guess secondhand vampire spiders are better than firsthand vampire spiders.

S E E Quine said...

` Hee hee... just wait a million years...