A species of wasp has been found using an unusual material for creating a protective barrier around its nest, lining its outer wall with the corpses of ants.
"Bone house" wasps, Deuteragenia ossarium, build their nests in cavities hollowed out in trees or in the soil, then protect developing eggs within by filling the front chamber in the nest, separated from the egg chambers, with as many dead ants as they can collect.
The name given to the newly-discovered species comes from historical human ossuaries, depositories where the bones of the dead are stored.
The females of the wasp species, found in southeastern China, don't hunt their ant victims for food, using them only as the macabre building material, a research team of German and Chinese scientists found.
Gathering that material is not without risk, says study leader and biologist Michael Staab from the University of Freiburg in Germany.
"Most of the ant specimens belong to a big ant species with a powerful sting," he says. "So the female wasp has a certain risk of getting injured or killed."
The wasps' corpse collections are reminiscent of massive skull racks erected in cities of Aztecs and some other Mesoamerican peoples that displayed heads taken from sacrificial victims to inspire fear, the researchers report in the journal PLOS One.
The decomposing ant corpses may be acting as a pheromonal warning to other insects to stay away, they say.
"It might work similarly to the skull racks, just not by vision but by scent," Staab says. "The ant chamber may give the wasp's nest the scent of a fierce ant colony -- and the nest is thus avoided by natural enemies."
It seems to work; the researchers said parasitism rates found in in 'Bone-house' nests were lower than in the nests of related cavity-nesting wasp species.
The females abandon the nest after laying their eggs, depending on the 'death wall' as a nest-protection strategy.
The nesting behavior of D. ossarium has no known parallel in any other wasp species or anywhere in nature for that matter, the researchers say.
"We don't know of any similar behavior in the animal kingdom, where dead bodies of another species are used to protect the offspring," says biologist and entomologists Michael Ohl of the Museum für Naturkunde in Berlin.
'Bone house' wasps are black with brown spots displayed on the wings. Females can be more than half an inch long, while males are somewhat smaller, the researchers said.
