Enlarge / 2023 marked the first sighting of a yellow-legged hornet in the United States, sparking fears that it may spread and devastate honeybees as it has in parts of Europe. (credit: Miguel Riopa/AFP via Getty Images)

In early August 2023, a beekeeper near the port of Savannah, Georgia, noticed some odd activity around his hives. Something was hunting his honeybees. It was a flying insect bigger than a yellowjacket, mostly black with bright yellow legs. The creature would hover at the hive entrance, capture a honeybee in flight, and butcher it before darting off with the bee’s thorax, the meatiest bit.

“He’d only been keeping bees since March… but he knew enough to know that something wasn’t right with this thing,” says Lewis Bartlett, an evolutionary ecologist and honeybee expert at the University of Georgia, who helped to investigate. Bartlett had seen these honeybee hunters before, during his PhD studies in England a decade earlier. The dreaded yellow-legged hornet had arrived in North America.

With origins in Afghanistan, eastern China, and Indonesia, the yellow-legged hornet, Vespa velutina, has expanded during the last two decades into South Korea, Japan, and Europe. When the hornet invades new territory, it preys on honeybees, bumblebees, and other vulnerable insects. One yellow-legged hornet can kill up to dozens of honeybees in a single day. It can decimate colonies through intimidation by deterring honeybees from foraging. “They’re not to be messed with,” says honeybee researcher Gard Otis, professor emeritus at the University of Guelph in Canada.

Enlarge / Xorides praecatorius is a parasitoid wasp. (credit: TorriPhoto via Getty)

If you puncture the ovary of a wasp called Microplitis demolitor, viruses squirt out in vast quantities, shimmering like iridescent blue toothpaste. “It’s very beautiful, and just amazing that there’s so much virus made in there,” says Gaelen Burke, an entomologist at the University of Georgia.

M. demolitor  is a parasite that lays its eggs in caterpillars, and the particles in its ovaries are “domesticated” viruses that have been tuned to persist harmlessly in wasps and serve their purposes. The virus particles are injected into the caterpillar through the wasp’s stinger, along with the wasp’s own eggs. The viruses then dump their contents into the caterpillar’s cells, delivering genes that are unlike those in a normal virus. Those genes suppress the caterpillar’s immune system and control its development, turning it into a harmless nursery for the wasp’s young.

The insect world is full of species of parasitic wasps that spend their infancy eating other insects alive. And for reasons that scientists don’t fully understand, they have repeatedly adopted and tamed wild, disease-causing viruses and turned them into biological weapons. Half a dozen examples already are described, and new research hints at many more.