Home & Garden Columns
It was an impressive object: somewhere between soccer ball- and basketball-sized, hanging just above eye level in a tanoak tree. A couple of its inhabitants, big black wasps with white markings, were at work on its outer surface. They were white-faced or bald-faced hornets, and the corrugated gray spheroid was their nest.
Hornets and their close relatives, the yellowjackets, represent one of the pinnacles of social evolution among insects. The vast majority of wasps are solitary, but one group of species has all the hallmarks of what biologists call eusociality. Only one female in the colony, the queen, reproduces; her daughters build, maintain, and provision the nest, and care for their younger siblings in their larval state. This state of affairs has evolved several times among insects—in ants and social bees, and the more distantly related termites—as well as in some species of reef-dwelling shrimp and that disconcerting rodent, the naked mole-rat. (Some spiders are colonial but not truly eusocial, and that’s probably a good thing).
Hornets and yellowjackets differ in their architectural style and preferred location. Hornets build out in the open, yellowjackets underground. Although their name is a byword for ferocity—think of the Hornet’s Nest at Shiloh, from which Union troops raked attacking Confederates with gunfire—hornets are actually somewhat less likely to attack humans than yellowjackets are. But neither is to be trifled with.
The nests of both types are similar in basic structure and construction material. They’re made of paper—wood pulp chewed up by the powerful jaws of the wasps and moistened with saliva—and contain tiers of cells, each built to house one of the queen’s eggs. Yellowjackets build to fill whatever nook or cranny they’re in; hornets add one tier below another, encasing the whole assemblage in a tough outer rind.
The project begins in spring, with a single female wasp who has mated the previous fall and overwintered. She makes a small paper disc, then builds it into a pedicel to which a row of cells is attached. Then she surrounds the whole thing with a paper envelope, leaving a hole in the bottom. She lays an egg in each cell; when the larvae hatch, she feeds them chewed-up insects. (Unlike solitary wasps, the social wasps don’t provision their brood cells with paralyzed spiders or caterpillars). After about 12 days as larvae and another 12 as pupae, the queen’s daughter’s emerge. They’re the work force now. The queen no longer hunts, builds, or feeds the brood; all she does is lay more eggs.
And more eggs, and more eggs. The paper city grows, tier after tier. One nest in California—and my hat is off to the man or woman who conducted this study—was found to have 4,768 workers in midseason, and over 10,000 cells. The workers dutifully kill more insects—I’ve seen yellowjackets literally cut a stick insect apart—and bring them home to feed the new mouths.
Then in late summer, a couple of things happen. The queen, who has stored last fall’s sperm and doled it out to fertilize the eggs that hatch into workers, lays a batch of unfertilized eggs that will hatch into male wasps. Other eggs, laid in larger-than-usual cells, get extra rations from the workers and develop into fertile females. They exit and mate. Those of the females who survive the winter will be next year’s queens. The males, having served their purpose, die off.
At some point after this exodus, the colony begins to come unraveled. Discipline breaks down. Instead of hunting insects to feed the larvae, the workers gorge on nectar and overripe fruit, and harass picnickers. They may even ransack the cells and eat any larvae that remain. During this period of anarchy, the queen, who has already ceased to lay eggs, dies. What’s interesting is that this all happens well before the first cold snap of the year. There will still be warm days in which the colony could have flourished. But like the superfluous males, the queen and the workers have done what they needed to do: created a new generation of queens. If it isn’t cleaned out first by a marauding skunk or raccoon, the paper city will be abandoned.
So the hornets I saw performing maintenance duty on that recent day on the downhill side of August were—although they had no way of knowing it—near the end of their road. All that work, all those wasp-hours of chewing paper and tending the brood, as part of a superorganismal queen-making machine, impelled, according to theory, by the drive to perpetuate the genes they shared with their fertile sisters. I just hope they were wired to experience some kind of job satisfaction.
This hornet colony may be home to thousands of workers. Photograph by Ron Sullivan.