Larva -- The larva of Scolia dubia is a legless, white grub with a brown head. It appears hairless and has no eyes. The antennae, maxillary and labial palps are one-segmented. There is a slit-like silk gland on the labium.
The wasps are present in North Carolina from June to October; however, in the Raleigh area, they are most prevalent during the month of August.
Feeding Habits -- Green June beetle and Japanese beetle grubs seem to be the primary host of S. dubia.
Damage -- No damage has been reported from these wasps. Homeowners, however, are often needlessly alarmed by the attractive scoliid wasps which are often abundant in August and September. Although scoliid wasps are virtually harmless and are beneficial in their control of beetle grubs, their presence in large numbers may indicate a large population of beetle grubs.
Life History -- One of the most common scoliid wasps in North Carolina is S. dubia, often referred to as the blue-winged wasp. These beneficial wasps lay their eggs on soil-infesting white grubs such as the larvae of May and June beetles and green June beetles. The adults feed on the nectar and perhaps on the pollen of flowers. They do not sting people unless greatly aggravated or captured in the hands. They fly several centimeters (a few inches) above grub-infested soil in a more or less figure-eight pattern.
Female wasps work they way through the soil in search of grubs, burrowing their own tunnels or following those made by grubs. On locating a grub, she stings and paralyzes it. She may burrow 1.2 cm deeper to construct a cell around the host. Then she lays an egg on the outside of the grub. The parasitized larva provides a fresh food supply for the wasp larva. The stung grubs never recover. Many grubs are stung, but only a few eggs are laid. These wasps, therefore, are very important natural agents in the control of grubs in the soil.