SMEARING the place you inhabit with faeces is, among people, an act of des­per­a­tion rarely seen out­side the con­fines of a prison. Some cock­roaches, though, do it all the time.

Rebeca Rosen­gaus of North­eastern Uni­ver­sity, in Boston, thinks she knows why. As she and her col­leagues dis­cov­ered in a study just pub­lished in Natur­wis­senschaften, wood-​​cockroach faeces pro­tect the insects from a par­a­sitic fungus. This finding, she thinks, may also explain the exis­tence of one of the world’s most suc­cessful groups of ani­mals: termites.

Wood cock­roaches nest in decaying tree trunks, in crevices they plaster with their faeces. These are also home to fungi that par­a­sitise their insect neigh­bours. Past obser­va­tions have hinted that cock­roach faeces pro­tect against such par­a­sitism. Dr Rosen­gaus decided to test the idea.

She and her col­leagues col­lected cock­roach faeces, mashed them up with water, mixed in fungal spores and smeared the mix­ture onto slides cov­ered in nutrient-​​rich agar. As a con­trol, they repeated the process without the faeces.

The fungus ger­mi­nated on all the con­trol slides. On those smeared with the faecal mix it ger­mi­nated on only a third. Faeces thus stop fungal ger­mi­na­tion and pre­sum­ably pro­tect cock­roaches. And what works for indi­vid­uals might work even better for a huge colony, in which indi­vid­uals ben­efit from the pooled exc­reta of thou­sands of neigh­bours. Which is where the ter­mite con­nec­tion comes in.

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