Scoliid wasps are large, somewhat hairy, solitary insects often mistaken for more aggressive social wasps or hornets due to their imposing size and vibrant coloration. They pose a minimal threat to humans because they lack the defensive instincts of colony-forming species and are primarily focused on finding food and mates. Understanding their behavior reveals why they are frequently observed in residential areas but rarely interact with people in a hostile way.
Identifying Scoliid Wasps
Scoliid wasps typically measure 5/8 inch to just under an inch long, with stout bodies. Their coloration is often a dark or metallic blue-black, frequently adorned with distinct, bright yellow, white, or reddish markings, most notably as bands or spots on the abdomen. For example, the common blue-winged wasp (Scolia dubia) has a dark body and two yellow spots on its abdomen.
A distinguishing characteristic is the fine, reddish or yellowish hair covering parts of their body, particularly the abdomen, making them appear furry. When flying, Scoliid wasps often exhibit a slow, meandering, low-to-the-ground pattern, sometimes flying in a loose figure-eight over lawns. This contrasts with the swift, direct flight of social wasps like yellowjackets.
Understanding Their Temperament and Sting
Scoliid wasps are solitary insects, meaning they do not live in colonies with a queen, workers, or a nest to defend. This lack of defensive instinct makes them non-aggressive unless they are directly handled, trapped, or accidentally stepped on. Only the female is capable of stinging, as males lack a stinger entirely.
The female’s stinger is primarily designed for paralyzing prey, not for defense against large mammals like humans. If a sting occurs due to provocation, the experience is generally described as causing localized pain, swelling, and mild redness at the site. While painful, the sting is typically less severe than that of a yellowjacket or hornet, and stings to humans are rare events. The venom is usually mild, but the main concern is a typical allergic reaction, which necessitates medical attention.
The Scoliid Wasp’s Role in Pest Control
The reason Scoliid wasps are often seen flying low over lawns and gardens is directly tied to their reproductive cycle and their beneficial ecological role. Adult female wasps search for the larvae of scarab beetles, commonly known as white grubs, which are significant pests that feed on the roots of turfgrass. These pests include the grubs of destructive species such as Japanese beetles and June bugs.
Once a female locates a grub underground, she will dig into the soil, sting the larva to paralyze it, and then lay a single egg on its body. The paralyzed grub remains alive but immobilized, serving as a fresh food source for the developing wasp larva. This parasitoid behavior effectively controls the population of these lawn pests, reducing the need for chemical treatments. As adults, Scoliid wasps also contribute to the ecosystem by feeding on nectar and pollen, which makes them incidental pollinators of various flowering plants.