Everybody in our family--even the dog--has been stung by a yellow jacket in the past few weeks. They are everywhere, not just in parks and backyards but on busy streets as well. You stop for a light on, say, Lincoln Avenue, and a yellow jacket flies through the window of your car and starts buzzing around the front seat.
Yellow jackets are always common in September, but this year they seem to have enjoyed a real population explosion. However unpleasant our subtropical summer may have been for people, it was obviously just right for wasps.
My wife got stung on the Ravenswood el. I got it in the middle of my back from a wasp that was apparently sitting on the car seat and got upset when I leaned against her. The dog got it on the foot, and my daughter was stung on the arm.
Only my daughter could trace her sting to the nest of yellow jackets on the back porch, a nest that I have been waffling on for three months: should I destroy it or leave it alone?
It does give a certain edge to hanging out on the porch. You step out the back door more or less into a cloud of hovering wasps. You have to learn to retain your cool while dangerous insects inspect your body. It is a valuable educational experience, a way to prepare yourself for encounters with the Hell's Angels or the Insane Unknowns. Don't get hysterical; don't make any sudden movements. Maybe they will just go away.
It is also the sort of thing you need to have around if you are a nature columnist. You have to be willing to endure nature if you are going to write about it.
Yellow jackets, as I said above, are wasps, members of the order Hymenoptera--a group that also includes bees and ants--family Vespidae, subfamily Vespidinae, genus Vespula. They are easily recognized. They are large insects, a half-inch long or more, marked by a pattern of black and yellow transverse stripes. They hold their bodies horizontally as they fly, and they often hover in one place, especially if the place is right in front of your face.
They are among the most social of wasps. Eusocial, Edward O. Wilson calls them in his book The Insect Societies, meaning that they possess three distinctive traits. First, they cooperate in caring for their young. Second, they display a division of labor in reproduction, with sterile individuals assisting fertile individuals engaged in reproduction. And third, at least two generations assist in the operations of the colony.
The life cycle of the colony on our back porch began sometime early this summer--I did not note the exact date--when a single insect, the queen, discovered a small opening in our porch railing, an opening that seems to lead to a large open space in a hollow pillar, a space that is ideal for a yellow jacket nest.
I noticed her slipping in and out and I gave some thought at the time to closing up the entrance at night and sealing her in. I hate to do things like that. It seems so suburban. I have only impressions to back this up, nothing like what scientists would consider hard data, but I think that we have far more insects in the city than they do in the suburbs.
Suburbanites are much more into poisons than we are, and their obsession with guarding the ethnic purity of their lawns leaves them with an impoverished selection of arthropods. Suburbanites are people who saturate their property with a mixture of Agent Orange and dieldrin and then say things like, "I couldn't live in the city. I like nature too much." Or, "I don't know how you can live in the city. I wouldn't feel safe there."
So I watched through the summer as the queen, the lone wasp who established our back porch colony, was joined by a growing horde of workers slipping in and out of that hole in the porch railing.
Queens are the only yellow jackets that live through the winter. They have been fertilized the previous fall. When they find a suitable nest site, they gather bits of wood and other plant fibers, chew them up, and saturate them with saliva to make paper. They shape the paper into a cluster of cells and deposit an egg in each cell. When the eggs hatch, the queen begins to bring food to the developing larvae. Adult wasps live on plant nectar, but the babies have a richer diet consisting mostly of insects prechewed by an adult. The adults will also carry off bits of food from your picnic table or your garbage can to feed their young.
The young from the first batch of eggs grow up to be sterile female workers. As soon as they emerge from the pupa stage, they begin to assist the queen in the job of expanding and maintaining the nest and gathering food for the young. As their numbers grow, they take over these jobs completely. The queen stays inside and lays eggs. She does not leave the nest at all.
As a group, wasps display several levels of social development. Some species are solitary; a single female digs a burrow and rears her young in it with no help from anybody. Some are semisocial. Among paper wasps, for example, several fertile females build a common nest.
Vespula wasps like our yellow jackets have well developed castes that seem to be controlled largely by nutrition. Colonies produce workers in early and mid summer when the population is small and only a few individuals are out foraging. By late summer, the colony has grown. There are more hunters out so there is more food. Nurse workers in the nest build larger chambers for eggs and then start stuffing food into the larvae in those chambers. Hawaiians used to do the same thing to members of their royal family. The powerful ought to look powerful.
These late-summer, well-fed larvae will become queens. They will mate with males--also produced only in late summer--and then go into hibernation. Next spring, they will found their own colonies.
Nutritional control of reproduction is regarded as a sophisticated method of keeping the lower orders in line. Among the more primitive, semisocial wasps, the queens use aggressive behavior, including eating the eggs of rivals, to maintain their monopoly on the production of the next generation.
I had always thought that feeding was a one-way street in a colony of social insects. Adults went out and got food, brought it back, and gave it to the larvae. But I have discovered that the process is actually reciprocal. The term entomologists use to describe this phenomenon is "trophallaxis," which is Greek for "to exchange nutriment." We could call it "food exchange," but things always sound more scientific in Greek.
Vespid larvae produce a salivary fluid that is close to 10 percent sugar. When an adult brings in, say, a prechewed fly for a larva, the larva spits out a bit of this juice and the adult licks it up.
This sweet saliva seems to function as a sort of food reserve for the colony. It has been calculated that the amount released in one typical feeding is enough to keep a worker going for half a day. It would also seem to serve as an additional incentive to the workers to keep feeding the young.
The level of interdependence that can be achieved through this mutual feeding was revealed in a study done in Israel of a wasp called Vespa orientalis. The study showed that adults of the species cannot convert protein to carbohydrates. Only the larvae produce the enzymes--chymotrypsin and carboxypeptidase A and B--that create this chemical change. So the adults feed the young on protein-rich insects, which the adults cannot digest, and the young convert some of the protein into growth and some into glucose, fructose, and sucrose that they feed to the adults.
The Vespula wasps that live around here are not as limited as the Israeli insects. Adult yellow jackets feed mainly on nectar and larval secretions, but they can eat meat if it is available. In fact, as winter approaches, they will begin to eat each other.
As the season advances, the population mix in the colony changes. Nonproductive males and queens begin to outnumber workers. Finally, the burden of supporting the ruling class gets to be too much, and the adults start to eat any remaining eggs and larvae in the nest. The colony has served its purpose. It has produced a new generation of reproducers who will carry on the species next year. October larvae are irrelevant and useless, so you might as well eat them.
By the way, this year's huge crop of yellow jackets means that there will be large numbers of queens hibernating, and, therefore, large numbers of colonies founded next spring. So barring a really bad summer for wasps in 1988, we will probably have another superabundance next September.