Newly Discovered Wasp Plugs Nest With Cork of Ant Corpses

Here’s a  great home security tip from nature: if you don’t want people breaking into your house, stuff your hallway with corpses. Ideally, use the corpses of dangerous and foul-smelling people.

For specific hints, you need to travel to the forests of China. There, Michael Staab from the University of Freiburg has discovered a new species of wasp that protects its young by stuffing the entrance to its nests with ant cadavers. The practice reminded him of European ossuaries—buildings like the amazing Sedlec Ossuary that are piled high and deep with human skeletons. In honour of these sites, Staab named the insect Deuteragenia ossarium. It’s the bone-house wasp.

Staab discovered the creature as part of a huge project to study the ecology of China’s forests. He was especially interested in spider-hunting wasps that nest in cavities, such as mud cells that they build themselves or tunnels bored by beetles. These insects are hard to spot. To study them, Staab’s team set up artificial nests, consisting of hollow canes strapped to a post.

Female wasps built their nests in 829 of these canes, and most followed a standard design. They drag a paralysed spider into the far end of the cane, lay an egg on it, and then seal it off with a plug of resin, plant matter, and soil. The wasp then returns with another spider and repeats the process, until the hollow cylinder is filled with a row of separated ‘brood cells’. When the young wasps hatch, they devour their spider meals, transform into adults, and then chew their way out through the plugs.

Staab saw this pattern again and again. But in 73 of the nests, he found a surprise: the final chamber was packed with up to 13 dead ants. You can see this clearly in the image on top. Each cell in the long cane contains the cocoon of a wasp grub which had long since eaten its spider. The ants are on the far left, like some gruesome corpse cork.

The wasp that emerged from these nests had never been seen before—a pitch-black, half-inch-long insect with a small golden beard. It was clearly part of the Deuteragenia group, but it’s the only one of the 50 known species that plugs its nests with ants.

“We do not know if it actively hunts for the ants or if the specimens are collected from the refuse piles of ant colonies,” says Staab. “However, since all ant specimens were in a very good condition and not seriously decayed, we think that the wasp does actively hunt living ants.”

He’s also certain that the antechamber protects the wasp’s young. Cavity-nesting wasps may be parasites that feed their young on spiders, but they have parasites of their own: flies and other wasps that lay eggs on their young. Staab found these ‘hyperparasites’ in 16 percent of the nests that he set up, but a mere 3 percent of the bone-house wasp’s nests.

He thinks the ants are responsible for this difference. Ants are covered in distinctive chemicals that help them to recognise each other and can persist on the shells of dead individuals for a long time. These chemicals could confuse parasites that are searching for wasp nests. They might also be active deterrents, since ants are powerful predators that viciously defend their colonies against intruders. Indeed, Staab found that the ant most commonly found in a bone-house wasp’s nest is a big aggressive species with a powerful sting.

Ants are such good predators that many animals use them to protect themselves. The caterpillars of blue butterflies turn ants into bodyguards and babysitters by mimicking their sounds and smells. The banded cat-eyed snake also lays eggs in the gardens of leaf-cutter ants. And one species of assassin bug covers itself with the bodies of the ants that it eats—a coat of many corpses that puts off spiders, and rivals the bone-house wasp’s ossuary in the grisly stakes.

Reference: Staab, Ohl, Zhu & Klein. 2014. A Unique Nest-Protection Strategy in a New Species of Spider Wasp. PLoS ONE 9(7): e101592. http://dx.doi.org/10.1371/journal.pone.0101592