Alien-Wasp Swarms Devouring Birds, Bugs in Hawaii

Christine Dell'Amore
National Geographic News
July 23, 2009

Attacking from nests as big as pickup-truck beds, invasive western yellowjacket wasps in Hawaii are munching their way through an "astonishing diversity" of creatures, from caterpillars to pheasants, a new study says.

Adult yellowjackets consume only nectar. But they kill or scavenge prey to deliver needed protein to their growing broods.

"They basically just carry it in their mandibles—you see them flying with their balls of meat," said lead study author Erin Wilson, who just finished her Ph.D. at the University of California, San Diego.

In their native habitat in the western U.S., the wasps die off in winter. But in Hawaii the wasps survive the winter, possibly due to mild year-round temperatures or subtle genetic changes.

A longer life-span gives the insects more time to build up their nests. So what would normally be a basketball-size nest can become, at the extreme, several feet long—big enough to fill the back of a pickup truck, Wilson said.

The extra room allows a colony of 50,000 workers to explode to 500,000 or more. Larger colonies mean that the insects deplete more prey than in areas where the wasps die off in winter.

(Related: "Stinging Wasps Moving North Due to Warming?")

Picnic Pests

Western yellowjackets—best known as picnic pests—were accidentally introduced to Hawaii during the 1900s, with the last wave of arrivals, in the 1970s, coming from the U.S. Pacific Northwest.

To learn more about the invaders' impact, Wilson and colleagues studied ten colonies in two national parks where the wasps are now widespread: Hawaii Volcanoes on the Big Island and Haleakala on Maui. (Hawaii map.)

The team collected bits of food from the jaws of 50 wasps and ran DNA analyses to determine what the insects had eaten.

Wilson had guessed that the aggressive bugs mostly go after slow-moving caterpillars and other "big, gooey organisms" and don't bother with many other types of prey.

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