Published in Yard and Garden News, August 1, 2007
Sphecid wasps are a familiar and diverse group of solitary wasps. During mid to late summer, sphecid (pronounced SFEE-sid) wasps are commonly found around their nests and flowers.
They vary from slender to stout-bodied insects. Some are less than half an inch long but many are larger, ranging from ½ to 1 ½ inches long (they can appear considerably larger when they are alive and active!). Many are black and yellow while others are black and orange and a few are iridescent blackish purple. These wasps are solitary, living in individual nests. However you can find many in a small area as a lot of species live together gregariously. Most sphecid wasps nest in the ground, while some nest in cavities, such as in hollow plant stems or cavities in wood, while a few construct nests made of mud.
Sometimes sphecid wasps are confused with bees. You can distinguish between them as bees are hairy and the ends of their hind legs are flattened while sphecid wasps are generally smooth and have normal-looking back legs. These solitary wasps can also be confused with yellowjackets, especially when they nest in the ground. However, most of the commonly encountered sphecid wasps are generally larger than yellowjackets. If you watch them, just one individual sphecid wasp goes into a nest but there may be many nests in one area. Yellowjackets, on the other hand, will have many different individuals entering and leaving a single nest opening.
Sphecids prey on insects or spiders which they paralyze and then feed to their young. They either drag the immobilized prey to their nest or they carry them back while they are flying. A particular sphecid wasp usually attacks a specific type of insect.
A common group of sphecid wasps are the thread-waisted wasps. They are recognized by the thin, conspicuous pedicel (actually part of the thorax) connecting the thorax and the abdomen. There are a couple of common species known as mud daubers. Sceliphron caementarium is about 3/4 to 1 inch long and is black with mostly yellow legs and yellow markings on its thorax. This insect visits moist soil to make balls of mud to build its nests which can be commonly constructed on homes. Another mud dauber is Chalybion californicus. Unlike S . caementarium, this wasp is black with just a little iridescence. It constructs its nests in cavities in plant stems and in buildings. However, instead of gathering mud like S. caementarium , it carries water to a source of soil near its nest to moisten it so it can use the mud to build its nest. Both mud daubers provision their nests with spiders.
Sphex wasps are large-sized types of thread-waisted wasps. They build their nests in the ground and are usually gregarious although they usually establish just moderate-sized colonies. Sphex spp. prey on katydids and crickets. We have two common species in Minnesota. Sphex pensylvanicus, also know as the steel-blue cricket hunter, is 1 to 1 1/4 inch long and iridescent violet-black with smoky black wings with a violet sheen. Sphex ichneumoneus, also called the great golden digger wasp, is a little smaller, usually just short of an inch in length. This wasp is brownish and yellow with reddish orange legs, a reddish orange and black abdomen and dark-colored wings.
Another thread-waisted wasp is Amnophila spp. This group is particularly slender with a long, thin petiole. They range in size from 5/8 to 1 inch long and are generally black with red or orange markings. These thread-waisted wasps are also ground nesters but typically are not gregarious, choosing to nest by themselves. They construct their nests and then temporarily seal them just before searching for food. They prey on caterpillar and sawfly larvae.
Sand wasps are another common group of sphecids in Minnesota. Probably one of the most familiar, and largest, of all sphecid wasps is the cicada killer, Sphecius speciousus. This striking wasp is black with a black and yellow banded abdomen and grows to a size of 1 to 1 ½ inches long. They prefer to nest in the soil and are quite gregarious, sometimes establishing large aggregations of nests. As their name suggests they primarily prey on cicadas. The males are very territorial and will buzz you to discourage you from their nests but they lack a stinger and can't sting. Females can sting but they are very unaggressive and usually avoid people.
Also watch for Bembix spp. sand wasps. They are stout-bodied insects possessing a dull black body with whitish or yellowish bands on their abdomen. They commonly nest in the ground in sandy areas, such as beaches and sand boxes where they are very gregarious. These sand wasps prefer to prey on flies, including horse flies.
If you encounter sphecid wasps on flowers, the are just feeding on nectar. They are harmless to plants and should be ignored. In fact, even when sphecid wasps are found nesting in your yard they should be tolerated as much as possible. They pose very little threat to people and are very beneficial because of the insects they eat. Although sphecid wasps may potentially sting to protect themselves, they are usually quite docile and nonaggressive towards people and will mind their own business when they are left undisturbed.