Discover more about this large insect family, whose species are social or solitary.
July 2011
By Lowell & Kaye Christie, F47246
Cartoons often show picnics invaded by hordes of ants, but this time of year, you are as likely to have flying visitors from the wasp family join in your festivities, particularly the ones called yellow jackets. As the summer progresses, so do the colonies of wasps, and if you know something about their life cycle, you’ll understand why there really are more of these flying critters around.
Although there are more than 100,000 species of wasps worldwide, they can be separated into two groups “” solitary wasps and social wasps. The solitary wasps, as their name implies, live alone, often underground. They seldom build nests. All males and females are fertile, and they often hunt other insects.
The largest wasp in the United States is the tarantula hawk, and as the name suggests, this species hunts one of the largest spiders, the tarantula. These wasps can grow to be 2 inches long and have a metallic blue-black body and beautiful orange or reddish wings. They inhabit the desert Southwest. The adult wasps dine on nectar, but they use the spider as a food source for their larvae. Only the female tarantula hawk is a hunter, using her sense of smell to track down the burrow of the spider. She will sting the spider, which is almost immediately paralyzed. The wasp then lays an egg on the spider and closes up the burrow. When the egg hatches, the spider provides food for the next generation of tarantula hawks.
Tarantula hawks have the most painful sting of any insect in North America, but, fortunately, they don’t have a particular interest in humans. You can watch them safely “” just don’t try to catch one. There seems to be a direct relationship between brilliantly colored insects and the intensity of their sting. The tarantula hawk is visible from a great distance, but its color warns off potential attackers.
Another colorful wasp with a nasty sting often is mistaken for an ant. In fact, the common name for the species is the velvet ant, but these insects are actually small wingless, flightless female wasps of the Mutillidae family. They prefer sandy and desert areas and can be found throughout North America. Their dense hair comes in bright red, silver, blue, or gold colors, and, like the tarantula hawk, these highly visible markings serve as warning signs to potential predators, advertising their dangerous defenses. No matter how cute these critters look, don’t try to pick one up.
These solitary wasps are fascinating to watch, but it’s the social wasps that are more likely to join you for lunch. Since the most typical visitor is the yellow jacket, we’ll use it as an illustration of the typical wasp’s life cycle.
There are actually 17 different species of yellow jackets in the United States, and each region has at least two species, one that nests above ground and the other that resides below ground. In all but the mildest climates, each communal nest is newly built each year, since the entire colony (with the exception of a few newly mated queen wasps) dies out when cold weather appears. The queen survives hidden in a protected area, and in the spring, as the temperature rises, she begins to build a new nest.
Yellow jacket nests are made of a paper-like material that consists of woody plant material mixed with saliva, starting with only a few chambers created by the queen. She lays eggs in these original chambers, and as they hatch into larvae, the queen hunts down caterpillars and insects to provide the protein needed by the young. Eventually the larvae become nonbreeding female worker wasps that gradually take over the nest-building and rearing duties from the queen. The queen’s sole function becomes producing more eggs, and the size of the nest increases.
By the end of the summer a wasp nest may have grown to the size of a soccer ball and, in the case of a yellow jacket nest, may contain several thousand individual wasps. The adult wasps feed primarily on decaying fruits, flower nectar, and tree sap, but with more and more larvae in need of protein, the search is on for additional food sources. That’s why you’ll find yellow jackets flying around garbage cans and picnic tables in late summer.
For most of their active season, yellow jackets are not very aggressive, although the introduced non-native European yellow jacket seems to be more of a problem than the native species. However, late in the season “” when we see them most “” they start to become much more protective of their nests and the area immediately around them. That’s when the new queen wasps (breeding females) are born.
Some research shows that in certain species of yellow jackets, swatting a wasp near the nest can be dangerous, because the wasp under assault releases a pheromone that causes the other wasps to go into attack mode. Fortunately, if you keep a distance from the wasp nest and don’t pick a fight, the wasps will usually leave you alone.
If it’s any comfort, only the female yellow jackets sting. The “stinger” is actually a modified ovipositor, a female sex organ. So if you see one or two of these yellow-and-black wasps, and you know that they are males, you can relax. The problem is telling the two sexes apart. We did find one resource that suggested this identification method:
It is possible to distinguish between genders of some wasp species based on the number of divisions on their antennae. Male yellow jacket wasps, for example, have 13 divisions per antenna, while females have 12.
Somehow, in actual practice, we don’t find that information very useful.