Female cockroaches living in groups with other females are more likely to have their unfertilized eggs hatch, a research team at Hokkaido University has found, providing a possible explanation for the reason the insect has managed to survive for hundreds of millions of years.

When three female American cockroaches ¡ª a species widely found throughout the world ¡ª were placed together in a study, ootheca, or the egg case of the cockroaches, formed more quickly than when a single female was observed, the team said.

¡°It explains well the fact that several female cockroaches will be able to maintain a colony in a more stable manner than a single female cockroach,¡± which can be regarded as a sign of cooperative behavior that is optimized for reproduction seen in other insects like white ants, the research team said in a news release Monday.

A group of more than 15 female cockroaches was able to maintain a colony for more than three years, indicating that ootheca form faster the more cockroaches there are, it said.

¡°We found that ootheca formation is facilitated when a female cockroach recognizes another female by touching it with their antennae, which are also used for smelling and tasting,¡± said Ko Kato, a graduate student who took part in the study.

Backing the findings, ootheca formation in a group of female cockroaches with severed antennae was slower than those with the sensory appendages, the team said.

In a case in which a female cockroach and a male cockroach incapable of copulating were placed together, the formation of ootheca took longer than the female-only group, the team said.

To exterminate cockroaches, ¡°It will be essential to prevent the spread of the females, as there are cockroaches that can expand their habitat range through parthenogenesis,¡± or asexual reproduction, the team said.

The findings will be published on the zoology journal website Zoological Letters.