Spider wasps are known (and feared) for having an intensely painful sting. Now there’s a new reason for revulsion: They build nests with the corpses of dead ants. The newfound species of spider wasp has been given an appropriately hardcore name: Deuteragenia ossarium, or “bone-house wasps,” after graveyard bone houses and ossuaries.
Ecologist Michael Staab and colleagues based in China and Germany came across bone-house wasps in southeast China’s Gutianshan National Nature reserve when they were collecting nest samples for a different project, and they describe them in a PLOS ONE paper published today. Wasps typically build nests at ground level and create chambers made of plant debris, resin, and soil, but they will also use abandoned cavities. Staab’s team capitalized on this by leaving out plastic tubes, called “trap nests,” in which wasps could build their nests.
After trap nests were colonized by wasps, Staab collected the traps and opened them with a knife to see what was inside. Mother wasps build nests to house their larvae, so as terrifying as larval wasps may be to a layperson, Staab was not surprised to find those. What was surprising was his discovery of a bunch of dead ants.
“The first time I saw it, I thought maybe I wasn’t seeing it clearly,” he said. “But then I found 10 to 15 more nests.” When the wasp larvae from the ant-filled nests hatched, Staab saw that they were all the same species. After analysis by taxonomic experts, the team discovered that they had stumbled upon a new species.
But why would wasps put ants in their nests? Staab and his colleagues think the bodies may help protect wasps’ nests through their scent. Ants communicate mostly by pheromones, and even after ants die, that scent lingers for days. Mother wasps abandon their larvae after nest-building, so the young are very vulnerable: Other animals co-opt wasps’ nests for their own eggs or break in to eat the larvae inside. Ants’ smell could deter animals from approaching the nest, especially if those animals have had bad experiences with ants in the past. They could also serve as an olfactory camouflage.
Staab and his colleagues are working with a chemist to figure out what compounds go into ant pheromones. “If we’re able to synthesize them, we want to do behavioral studies,” says Staab, such as testing whether ant pheromones really do repel parasites.
The researchers also want to determine how wasps get ants for their nests. Do they collect dead ants or hunt live ones? Staab thinks the good condition of the ants means they were freshly killed. “They were not decayed or molded,” he said, describing the ants he found. “That leads us to the assumption that they probably hunt live ants.”
Plus, like other spider wasps, the bone-house wasps hunt spiders. And the way a mother spider wasp does so is truly horrifying: She stings a spider, paralyzing it, then drags it back to her nest. There, she eats the non-essential parts of the spider, like its legs, leaving the body immobile but still alive. “That way, it is preserved for her larvae,” says Staab. Finally, she leaves it in the nest for her larvae to consume after she abandons them there.
So, while a spider wasp’s sting may be akin to “dropping a running hair dryer into your bubble bath,” as one entomologist describes it, you can be grateful that it can’t dismember you, let its young eat you alive, or use your corpse as a nest decoration.