Scoliid wasps are a family of beetle hunters. Large, rather hairy solitary wasps, some species are handsomely colored. The female digs in soil, finds a beetle grub, stings it, and lays an egg on it. The young eats the beetle grub. The name is pronounced sko-LEE-ud.
Coloration includes the typical wasp colors: bodies are usually dark or black, often with a bluish sheen, and the markings may include yellow stripes or other patterns of white, yellow, orange, or red. The precise pattern helps identify the species.
Specialists use wing vein patterns and details of the antennae, reproductive organs, and other anatomy to make precise identifications. In some species, the females and males look very different, which can complicate IDs.
Scoliid wasps are large, with hairs visible on their abdomen. The wings have distinctive corrugations: lengthwise, roughly parallel wrinkles on the outer half or two-thirds of the wings.
These wasps also have a rather bent or curled posture. The family name comes from the genus name Scolia, which has the same root meaning “bent,” or “crooked,” as in scoliosis, or curvature of the spine.
Most North American scoliids occur in the Southwest, Florida, or other desert, tropical, or subtropical areas. Some common Missouri species include:
- The blue-winged wasp (Scolia dubia) has a wide range in North America. The colors on its abdomen are distinctive: a large, fuzzy, rich rusty patch with two ovals of yellow. This quickly distinguishes it from other large wasps with shiny blue-black bodies and wings.
- The double-banded scoliid (Scolia bicincta), with its two cream-colored bands on the front half of the abdomen, resembles a mason wasp. Like other scoliids, it is hairy and usually seen visiting flowers.
- Scolia nobilitata (no common name, but you could call it the noble scoliid) has a wide distribution in the United States. It is small for a scoliid, just over ½ inch long. Legs are reddish, and the wings are dark. Females have 2 or 3 pairs of yellow or orange spots on the front part of the abdomen. Males are variable and frequently have yellow-banded abdomens.
- Pygodasis quadrimaculata (formerly in genus Campsomeris) is very large, and females have four large, yellow ovals on the abdomen. It looks like a huge, black-legged version of Scolia nobilitata. The color pattern of males can vary; they are frequently banded. It occurs in the eastern United States.
- Dielis plumipes (formerly in genus Campsomeris) is another very large, heavy-looking, hairy wasp. It has amber wings and cream-colored or yellow bands on the abdomen. It might easily be mistaken for a cicada killer wasp.
Similar species: There are many other families of large wasps that have similar colorations, including the spider wasps and thread-waisted wasps. Hairs on the abdomen, thorax, and legs, and typically bent-over posture help to distinguish the scoliids.
Habitat and Conservation
In Missouri, most people see adult scoliid wasps as they are busily drinking nectar from flowers, in the hottest time of the year: July, August, and September. Thus they are usually found in yards, gardens, old fields, pastures, prairies, and other open places with plenty of flowers.
In early morning, males of some species of scoliids are sometimes seen resting, their bodies curled around a plant stalk, fast asleep. They often do this in groups. Scoliids are not the only bees or wasps where the males sleep in groups on plant stems. It may help them to avoid predation during the night.
Underground, the larvae eat the grubs of beetles in the scarab family, to which the female has attached their egg.
Adults take nectar from flowers, and this is where most people see these wasps.
Gardeners, get excited: scoliid wasps dispatch many pest beetles, including the destructive, nonnative Japanese beetle as well as native May beetles (June bugs) and the green June beetle. Females dig into soil. When they locate the grub of a scarab beetle, they sting it if necessary and lay an egg on it. In some species, the female wasp digs farther into the ground, creating a deeper chamber for her larva and its grub meal. The larva hatches, consumes the grub over the course of a few weeks, pupates, then emerges, digging its way out of the ground, as an adult scoliid wasp. Apparently, overwintering occurs underground in the mature larval stage or as a pupa.
In our area, most adult scoliid wasps are seen in late summer: August and September. Apparently, adult emergence and activity is timed after the beetles’ heyday, so that the female wasps can dig and locate suitably developed beetle grubs.
Gardeners in Missouri are sick and tired of nonnative Japanese beetles chewing up their roses, grapevines, crape myrtles, and other plants. And not many people appreciate the white grubs of May beetles (June bugs) eating the roots of their lawn grass and creating brown patches in their lawns. So gardeners should be filled with joy — or at least a sense of grim satisfaction — when they see these wasps in their yard.
One of the most fascinating and useful areas of biology is the field of insect-host parasite interactions. These biologists study the specific ways that certain insects parasitize and devour each other. To the people who study it, it’s like unraveling a bizarre sci-fi mystery every day. But the upshot for human interests, especially for agriculture, is enormous.
What a great example of the connections between climate, plant growth, beetle life cycle, and wasp emergence! The emergence of the leaf-eating beetles is perfectly timed to take advantage of the explosion of plant growth in our region, in late spring and early summer (that’s why they’re called May beetles and June bugs). The wasps emerge in perfect time to take advantage of the many beetle grubs while they are still fairly close to the surface, before the grubs move lower in the soil in preparation for winter.
Many other animals eat beetle grubs, too, including skunks, armadillos, moles, shrews, snakes, crows, and grackles. The scoliid wasps compete with these animals for grubs. No doubt many grub-eating animals consume scoliid larvae along with the grubs.
Adult scoliid wasps, as they collect nectar to sustain themselves, also help to pollinate plants.