Social Insects and Matricide: Why Some Bees, Wasps, Ants Kill Their Nearest Relative

Some social insects kill their mother. There, we said it. Why do they do that? An entomologist from the University of California Riverside, Kevin J. Loope, wanted to know and recently published a report on his findings in the journal Current Biology.

Loope began to wonder after reading about matricidal behavior among some social insects, a release noted. In general, these insects, including ants, wasps and bees, spend their lives not killing their mother. The workers--all female--work instead of reproducing, while the queen is left free to bring new offspring to the hive or colony. But why does matricide occur in some cases?

"People think of social insects as workers toiling mindlessly for the good of the queen or the colony. But it appears that workers are more calculating, and help or harm the queen depending on the circumstances they find themselves in," observed Loope in the release.

In the study, Loope observed colonies of yellow jacket wasps in his lab, filmed them in continuous tracks with video cameras, then was an innocent bystander when they killed their mother. In addition, he gathered wild colonies to increase the size of his study sample. From observing behavior, he concluded that worker wasps perform matricide when they have many full siblings, but not when their colonies are mixes of half and full siblings.

"Workers are assessing the situation in their colony and deciding to revolt against the queen only when the genetic makeup of the colony makes it favorable to do so," Loope said in the release. "The main advantage is to allow your sister workers to lay male eggs, rather than the queen, who typically stops worker reproduction by egg eating, attacking reproducing workers, and by laying many of her own eggs. By eliminating the queen, a matricidal worker allows other workers and herself to lay male eggs."

Male social insects have short life spans--born at the end of the year, later mating with the new queens, then dying. Even though worker insects don't mate, they can lay male eggs because of an oddity in their genetic make-up. The study notes that at times the workers compete with the queen for production of males, the release confirmed.

"They only altruistically give up reproduction when the context is right, but revolt when it benefits them to do so," said Loope in the release.

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