Scientists in New Zealand did an experiment with wild insects that studied the common wasp, an alien invader to the island country, competing for food with the native ant species Prolasius advenus.
When the wasp approached a mound of food swarming with ants, it would pluck an ant from the pile, fly a ways off, and drop the living insect from its jaws.
Common wasps (Vespula vulgaris) are native to North America but were introduced to New Zealand in the 1970s. The wasps eat nectar and other insects, capturing live prey or scavenging.
This led to the establishment of an experiment where wasps and ants were presented with samples of high-protein food: little chunks of tuna fish.
The samples were placed at 48 stations in a natural beach forest; cameras were set up near each one. Both ants and wasps visited 45 of the 48 stations, and the cameras recorded 1,295 interactions between the insects.
Most of the time, the ants and wasps avoided one another. Although, the researchers documented 341 cases when the ants were aggressive toward the wasps, charging, biting or spraying them with formic acid; a natural defense mechanism.
In only 90 encounters the wasps were the aggressors, including 62 cases of ant dropping. The researchers suspect the other 28 times were ant-dropping attempts which the wasps botched.
In the majority of the cases, the wasps’ ant-dropping behavior was unprovoked, ants being grabbed and flown away. Sometimes the ants were unruly before they were grappled and carried off.
The team argues that the acid defense may be why the wasps “ant drop” rather than just killing the smaller insects outright.