"The next day we came back and the ground was littered with Argentine ants. There were dead ants all around and there was a lot of fighting around the nest entrances."
In earlier observations, the students had noticed the winter ants occasionally secreting a whitish fluid from their abdomens and, by prodding a few with a paperclip, had figured out that the ants tended to secrete when hassled.
"They would curl their abdomens around and deposit the white secretion on the paper clip used to prod them," said Trevor Sorrells, then a junior who was a teaching assistant for the class.
Watching the combat, the students saw the winter ants use their lethal secretions against the invaders. Intrigued, the group decided to continue the research after the class ended.
Kuritzky did a chemical analysis of the secretion, using gas chromatography and mass spectrometry. She determined that part of the secretion consisted of a type of hydrocarbon, which many social insects use to carry a colony-specific odor that helps them identify friend from foe. But what substance gives the secretion is lethal punch still has to be determined.
"Whatever it is, it is clearly very toxic," Gordon said.
To assess the lethality of the secretion and how freely the winter ants wielded it Sorrells and the other students ran a series of "trials by combat" in palm-sized shallow glass petri dishes in the lab.
He organized some group rumbles with 20 ants per dish, varying the ratio of winter ants to Argentine ants to see if that had an effect. He also ran some one-on-one gladiatorial combat in a one-centimeter square "ring."
"It turns out the winter ants use the secretion only when they are really overwhelmed, so it is probably energetically very expensive for the winter ant to manufacture and use this stuff," Gordon said.
In the great outdoors, without petri dish arenas in which to settle their disputes, the winter ants
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