Wasps are notorious for devouring other creatures from the inside out. Now scientists have learned that after they have killed something, they wrap themselves up in its cocoon for good measure and exhibit strange jumping behaviour while in that cocooned state. Bathyplectes anurus wasps are not perilous to humans, but for the alfalfa weevil, they're a nightmare incarnate. The wasps find cocooned weevil larvae and inject their eggs into them. The young wasps eventually hatch and burst out of the cocooned weevil larvae, using them as a food source.
Just because the wasp has no more use for the weevil larva body doesn't mean it's over. Wasps know very well the dangers that can befall a cocooned animal, and they take measures to prevent themselves from experiencing the weevil's fate. Although they spin a cocoon of their own, they do so only inside the weevil's own cocoon, using it as an outer defence.
They also retain more mobility. Some wasp cocoons, including those made by Bathyplectes anurus, hop around a lot. A recent study done at Kyusho University found out that jumping a lot made the wasps smaller upon hatching. There's only a limited amount of food for the wasp, and if it uses its energy on jumping, it can't grow as well.
So why do they jump? Wasps tend to hop away from hotter conditions. The warmer the Japanese researchers made the environment around the larva, the more they hopped. They also hopped more in brighter conditions and less humid conditions. And they hopped to get away from predators. When the researchers put Japanese giant ants near the larvae, the hopping commenced in earnest, meaning the larvae know they need to get away from specific predators while still in the cocoon.
The researchers only looked at a few larvae at a time, but things can get borderline-horrifying when large amounts of larvae are all together. One person, who heard a "sizzling sound" from a ditch, found that the noise was really thousands of wasp larvae, and hopping over each other to get away.