Named Hydrophylita emporos—emporos is Latin for “passenger”—the female wasps were observed clinging to abdomens of damselflies, an aquatic insect related to a dragonfly. This acrobatic feat eventually pays off: When the damselfly starts laying its eggs on a submerged leaf, the wasp walks down the abdomen of the damselfly like it’s an exit ramp, enters the water, and then lays its own eggs in the damselflies’ eggs. (See “‘Zombie’ Roaches Lose Free Will Due to Wasp Venom.”)
Watch a video of the wasp climbing on the damselfly.
This is “very clever” on the part of the wasp: The quicker access to fresh eggs, the better for the wasp, said study co-author Andrew Polaszek, head of the Division of Terrestrial Invertebrates at London’s Natural History Museum.
Study leader Yuan Tung Shih first saw the wasp-on-damselfly behavior in the wild in Taipei, Taiwan, and told his adviser Polaszek, who was amazed but needed proof. When Shih sent him specimens and a video of the behavior, Polaszek “knew it was something special.”
“I’ve got 25 years of experience doing this, and when I looked at these things I didn’t know what family they belonged to,” said Polaszek, who eventually placed it in Trichogrammatidae, the family of the smallest known insects—the tiniest is 0.17 millimeter.
For one thing, H. emporos looks nothing like other wasps in its genus—it has long, delicate features instead of the “short, stumpy” antennae and legs of its relatives—differences that are still unexplained, he said. The females also have bigger “claws” than other wasps, perhaps an adaptation to walk in freshwater currents.
The wasp’s relative ease in living both in and out of water also surprised the team. For instance, some H. emporos never leave the water after hatching—males, which appear to be very rare at about 125 females for one male, likely stay underwater their entire lives, according to the study, published July 24 in the journal PLoS ONE. (Read: “Parasitic Wasp Swarm Unleashed to Fight Pests.”)
Other parasitic wasps ride on their hosts—it’s a practice called phoresy—but it’s the first time it’s been seen in the Hydrophylita genus, Polaszek added.
Robert Matthews, a professor emeritus of entomology at the University of Georgia, pointed out by email that the newfound wasp and others in its family are notoriously weak fliers, whereas damselflies are agile and highly mobile fliers.
So by hitching a ride, the newfound wasp has “neatly solved the problem” of how to access new hosts with little apparent risk, said Matthews, who was not involved in the study.
But intriguing questions remain, Matthews said, including what cues the wasp receives before it jumps on a damselfly—for instance, how does the wasp know whether it’s a male or a female damselfly? (Also see “Wasps Can Recognize Faces.”)
What’s more, he’s curious about why there are so few males. “Mating behavior,” he said, “will likely prove to be interesting.”