Why Do Wasps Kill Their Mothers?

Colonies of social insects like ants, bees and wasps are often thought of as superbly well-oiled machines—ones that are made up of individual insects that perform specific roles assigned by birth until the day they die. Typically, colonies are led by queens that give birth to the next generations of queens, and the workers or drones help ensure the continued functioning of the colony. So why do Insects kill their Mothers?

One curious event has been observed in these colonies: Workers sometimes kill their queens, despite the fact that these queens are actually their own mothers.

What could be spurring these workers into taking such action against the queens of their colonies?

A closer look at Wasp behavior

A postdoctoral researcher at the University of California, Riverside names Kevin J. Loope has conducted research to get at the bottom of this mystery. He reared 18 colonies of yellow jacket wasps in a lab, along with 31 mature colonies from the wild that exhibit signs of the alleged matricide, (such as lacking a queen).

To understand the structure of colonies, keep in mind that a single queen wasp establishes a colony by giving birth first to female workers; later, she will give birth to male drones and new queens. These young queens will eventually fly off to mate with males, hibernate, and start their own colonies elsewhere.

Female workers spend their lives taking care of and defending the nest, gathering food, and helping the queen give birth. But as previously mentioned, there are times when these female workers would kill their queen—their mother.

Loope studied the genes of female workers from 21 of the 31 colonies he gathered. He discovered that workers killed the queen when the colony has a lot of full siblings (or many of the members of the colony had the same father); this did not happen when the colony is made up of a mix of full and half siblings.

The occurrence of matricide would depend on the workers’ ability to lay eggs. Although thought to be sterile, some female workers can give virgin birth to male eggs. However, if this happens, the queen would eat the workers’ eggs and attack the egg-laying workers.

Studying Wasp evolution

These actions are thought to be influenced by an evolutionary drive among organisms to typically favor close relatives over more distant ones.

If a queen wasp would die (get killed), theoretically, female workers could then lay male eggs. If all of these workers are siblings, then all the resulting males would be their sons or nephews. This assures them of a greater chance of passing on their genes.

On the other hand, if the queen dies and the female workers are not closely related, the males they give birth to would be either sons or more distant relatives, which reduces their chance of passing on their genes.

The study reveals that rather than being mindless automatons that simply work for the benefit of the queen and the colony, female workers are “more calculating, and help or harm the queen depending on the circumstances they find themselves in,” according to Loope. If they can tell that the colony consists of more distant relatives than close ones, the female workers will revolt against their “sterile” status and look after their own interests of passing on their genes instead of the queen’s.

Essentially, the research shows how social insects can respond adaptively when they are faced with conflicting interests as to how the colony should move forward, genetically.