The introduced wasps' taste for flesh shocked her—the insects' prey spans 14 taxonomic groups of animals, including tree lice, spiders, rats, and geckos.
Although the wasps don't kill larger animals such as birds and lizards, they do scavenge them, the team reports this week in the journal Proceedings of the National Academy of Sciences.
In addition, the adult wasps collect huge amounts of nectar, draining resources for native insects and birds such as the Hawaiian honeycreeper.
The wasps' hunger for nectar may even be disrupting pollination of native plants, the study authors write.
Overall, the wasps have been filling in the role of top insect-eater, left open as Hawaii's bird populations dwindle.
But Wilson said that prey insects can easily rebound if yellowjacket nests are removed.
Spiders and caterpillars that had been locally wiped out have returned within a few months when nearby wasp nests were taken out, Wilson said.
Picking apart the wasps' "little masticated balls of prey items" and analyzing their molecular structures was an important part of this study, said P. Kirk Visscher, an associate professor of entomology at the University of California, Riverside, who studies social insects.
"It's one of the earlier applications of this [technology, and a] nice demonstration of what it's capable of doing," he added.
Without the DNA work, the researchers would not have been able to identify the precise species that the wasps were collecting.
But according to Visscher, yellowjackets eat pretty much anything in their native habitats, so their wide-ranging Hawaiian diet is "not very surprising."
"Straight for the Head"
Even with an expanded Hawaiian menu, the wasps' vicious killing strategies haven't changed in their new habitat, lead study author Wilson said.
"If you have something like a caterpillar, they'll take their time a bit more, jump on it, and cut it into pieces," Wilson said.
"If you have something that can fight back, like a honeybee then they go straight for the head," decapitating the bee to disable it.
"The honeybee will still be moving—it's pretty gruesome."
And although humans aren't exactly on the menu, Wilson has been a target of the aggressive insects during her fieldwork.
"You always get stung," she said. "They can sense any heat that's escaping from your [bee] suit, and if you have a tiny little hole, they'll get you."
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