By Dr. Becker
Nest-building members of the insect kingdom use a variety of nest protection strategies to defend their eggs from predators. Wasps, for example, dig holes in which to nest, or move into pre-existing holes, such as in wood. These nests contain brood cells separated by thin layers of soil, resin, or plant debris.
Recently, scientists discovered not only a new species of wasp, but also a new, rather dark twist on its nest building behavior.
Research Team Makes Two Important Discoveries
Michael Staab, a researcher at the University of Freiburg in Germany, and his colleagues were studying cavity-nesting wasps in southeast China. They set up trap nests in a subtropical evergreen forest in the Yangtze River Basin.
When they gathered the trap nests for examination, the researchers were surprised to discover that several dozen had an outer cell packed tight with, of all things, the whole bodies of dead ants. And to their further astonishment, inside the nests was a never-before identified species of spider-hunting wasp.
Staab and his team named the newly discovered insect the “bone-house wasp” (Deuteragenia ossarium), after graveyard bone-houses or ossuaries (containers that hold the bones of the dead).
This image depicts a 'bone house' wasp nest protection overview
Credit: Staab et al, doi:10.1371/journal.pone.0101592; CC-BY
Does the Scent of Ants Frighten Predators?
The researchers were stumped by why the wasps chose to use dead ants until they realized the tiny corpses were always located in the outer vestibular cell of the nest. The vestibular cell is a structure the female wasp builds to close the nest after she lays her eggs, and it is usually empty. Once the nest is sealed, the female wasp abandons it. She doesn’t take care of her young or provide protection beyond what the nest offers.
Staab and his colleagues suspect the bone-house wasps may use dead ants because of their smell, which could provide a chemical cue to predators to stay away. As it turns out, ants are fiercely protective of their own nests, and the type of ant the wasps use to build with is an aggressive species with a painful sting. So it could be the wasps’ nest protection strategy helps insure the survival of their larvae.
The research team noted that the ant bodies in the vestibular cells were in very good condition, which led them to conclude the wasps actively hunt and kill the ants rather than simply collecting dead ants as they find them.
Many other species also use ants for protection, for example, certain spiders and butterflies, but they typically disguise themselves and live inside an ant colony.
Other species of wasps also employ some rather grotesque measures to insure their larvae make it to wasp-hood. A species of parasitic wasp, for example, lays its eggs in a particular type of spider. The larvae then eat their way out of their host.
Ant Aroma May Also Deter Parasites
According to the study’s findings, which were published in the open-access journal PLOS ONE,1 only 3 percent of the bone-house wasp larvae had parasites, which is low compared to around 16 percent of larvae parasitized in other nests the research team inspected. Since the corpses are coated with complex chemicals the ants use on their exoskeleton, it’s possible that parasites and predators mistake the wasp nest for an ant colony and leave it alone.
"Our discovery demonstrates in an impressive way, what fascinating strategies of offspring-protection have evolved in the animal kingdom,” said Dr. Staab.