The amber-colored victim is known as the "crypt gall wasp" (Bassettia pallida). It nests in tiny cavities called "crypts" on its host tree, which provides free nutrition throughout its development. When the adult wasp is ready to leave, it chews a hole through the tree's woody tissue and makes its way out. But for some gall wasps, things don't go according to plan. [The 10 Most Diabolical and Disgusting Parasites]
Instead of exiting the hole they make, the wasps would plug the holes with their head and die, researchers found. This is because the wasps are being manipulated by another crypt-residing wasp that capitalizes on the gall wasps' ability to chew a hole for its own exit. After the "crypt-keeper wasp" gets its host to create a hole, it eats its own way through the host. This grisly behavior earned the wasp its scientific name, Euderus set (Set being the ancient Egyptian god of evil).
To learn how the wasp benefits from manipulating its host into plugging the hole, scientists covered some head-plugged holes with bark. When the crypt-keeper wasp had to get through the extra bark, it was three times more likely to get trapped in the crypt and die than a wasp that had to get through only the head and no bark, said lead study author Kelly Weinersmith, a parasitologist at Rice University in Houston.
"So, it looks like the specific purpose of the manipulation is to help the crypt-keeper wasps emerge, because they are weaker excavators than their hosts," Weinersmith told Live Science. "They need the hosts to do that work for them, so they can get out."
Details of how a crypt-keeper female zeroes in on a developing gall wasp's crypt are yet to be uncovered. Weinersmith thinks a female either lays an egg directly into the body of the host or into the crypt next to the host using its egg-laying organ.
|In this photo, the bark has been dissected away to reveal two Bassettia pallida adults residing within their crypts.|
|The crypt gall wasp, Bassettia pallida.|
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