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Species: European earwig (Forficula auricularia)

Habitat: Woods, gardens, vineyards and orchards of Europe and North America

Desperate times call for desperate measures. As food shortages hit, European earwig babies resort to eating each other’s faeces in their underground homes, helping to keep hunger and death at bay.

In times of plentiful food, the earwig offspring, or ‘nymphs’, feast on scraps of plant and insect material that their mother brings back from her trips above ground, and on .

But when faced with limited supplies, the nymphs have to make do with what’s around them to survive.

Unlike many other insects that live in groups, European earwigs don’t clear their nest of faeces. Availability of faeces in hard times keeps the nymphs alive for about two more days on average than without them, researchers have now found.

In the lab, researchers deprived 56 five-day-old nymphs of food, and offered 28 of them faeces from their siblings. Nymphs with nothing to feed on survived for an average of 14 days, but those with access to their siblings’ faeces lived for an average of 16 days. According to of the Johannes Gutenberg University of Mainz in Germany, this is probably because the faeces of nymphs are poorly digested, so there are leftover nutrients.

Faecal supplements

Körner’s team also presented 60 nymphs with a choice between regular food and faeces of their nest mates. A total of 48 nymphs preferred food over faeces, but around half of these supplemented their diet with some faeces – indicating that something else, in addition to the simple aim of survival, may be at play.

Munching on faeces might be a crucial way for the young to acquire essential gut microbes, says Körner.

The nutritional and microbial gains from exchanging faeces may even have kept earwig offspring from straying and probably gave rise to family life in the species, says Körner.

Earwig nymphs are not completely dependent on their mother for food: once they get past their first, crucial stage of development, they can leave the nest and fend for themselves. But the benefits of sharing faeces as food might be the reason nymphs stick around until they mature into adults.

“This is very likely to be an early form of sociality that is maintained for a long time. There is competition but some benefits of staying with your siblings,” says Körner. “You will benefit from the overall food availability even if you didn’t get enough by yourself.”

“Unfortunately, we cannot go back in time to see what environmental factors, including diet, were responsible for the evolution of social tendencies,” says  at Northeastern University in Boston, Massachusetts. “So the manipulations performed by the authors are only a first step to understand the dynamics between environmental stress and sociality.”

Although the evolution of any trait is probably the end result of multiple genetic and environmental factors, she says, “the added benefit of sharing [nutrients] with others was probably one of the several factors that influenced the evolution of social behaviour in some insects”.

Journal reference: Behavioral Ecology, DOI:

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