Scientists have discovered how cockroaches recognise ‘their own’

Immediately after hatching, the gut of young cockroaches contains almost no bacteria, which they need to survive.

To obtain these bacteria and additional nutrients, they feed on the waste produced by adult cockroaches in their group. At the same time, the young insects become familiar with the characteristic odour of the place where they grew up.

This odour may vary slightly from one group to another. It is influenced by diet, living conditions and the bacteria present in the cockroaches’ bodies.

Details

Scientists compared two groups of young cockroaches. One group lived alongside other cockroaches from the moment they hatched and fed on their waste. The other group did not have this experience.

The cockroaches in the second group showed equal interest in the odours of different colonies. They did not yet know which odour to regard as familiar.

However, the insects that had grown up alongside their own group were later more likely to choose that particular scent. This suggests that they had memorised it and could distinguish it from unfamiliar scents.

In another experiment, the scientists associated one of the odours with sweet food.

Afterwards, the cockroaches were more likely to head towards the scent near which they had previously received a treat. In this way, the researchers confirmed that the insects are capable of learning from their own experience and remembering useful cues.

Essentially, the scent acts as a cue for them: food, shelter and other cockroaches may be nearby.

German cockroaches do not form complex families or colonies, like bees or ants. However, they live in groups and are able to remember the scent of the place where they grew up.

Therefore, the expression ‘they recognise their own’ should be taken with a pinch of salt. Cockroaches do not identify relatives nor do they experience feelings of friendship. They simply prefer the familiar scent of their own group.

This behaviour helps them to stay in a safe place where there is food, shelter and the bacteria their bodies need.

This discovery may help in the fight against cockroaches

Young cockroaches rarely stray far from their group, as they find everything they need nearby. Because of this, conventional traps and poisoned baits may be less effective.

Scientists suggest that, in the future, it may be possible to create a scent that attracts cockroaches from different groups. This could then be added to traps and baits.

There is no such universal solution as yet. The research has merely shown which odours influence cockroach behaviour and why the insects gather in one place.

Why this is important

The study has shown that cockroaches’ behaviour depends not only on innate habits. They are capable of remembering odours and altering their behaviour based on their experiences.

This helps us better understand why cockroaches form persistent clusters and why it can be difficult to lure them out of their hiding places.

Source

Study: Ayako Wada-Katsumata et al. Group recognition in the German cockroach, a subsocial omnivore, is based on faecal odour preference that is modulated by coprophagy, diet and learning.

Journal: Proceedings of the Royal Society B: Biological Sciences, 2026.