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These suicidal aphids repair their home with their own bodily fluids

The gall aphid’s home repair strategy gives new meaning to the phrase “sweat equity.” These insects use their own bodily fluids to patch holes in the walls of their colony’s home—a hollow growth called a gall that forms on the branches of trees where they set up shop. Once an invader pierces the gall, the aphid soldiers lay down beads of a thick, milky fluid from their abdomens and don’t stop until they seal the breach. Some wring themselves dry until they are lifeless husks, others drown in their own secretions, and a few trap themselves outside—all to ensure the safety of their brethren inside the gall.

But scientists didn’t know what this goop was made of or how the gall aphids (Nipponaphis monzeni) produced it. Now, researchers have untangled the biochemical recipe for the aphid’s natural building materials.

To study the aphid’s natural mortar, researchers first collected it from galls on winter hazel trees in Japan in spring, when they first form. When they put the fluid under the microscope, they discovered scores of what looked like blood cells packed with oily lipids. Biochemical analysis revealed the presence of the enzyme phenoloxidase, the amino acid tyrosine, and a previously unknown protein.

When mixed together by the aphid soldiers’ legs, the lipid-laden cells rupture and then the ingredients clot and harden like a scab in about an hour, the researchers report today in the Proceedings of the National Academy of Sciences. Other bugs use these same ingredients to seal wounds and keep out infections—but in this species, they’re produced in mass quantities to defend the colony.

The authors say understanding how the gall aphid’s extreme teamwork evolved could offer insights into how natural selection leads to specialized social adaptations in other species. Their next step is to figure out how the aphids trick plants into forming galls in the first place. They plan to start with a close look at another of the aphid’s bodily fluids—its spit.