Sclerodermus, a Small Wasp that Occasionally Infests Homes

Summary

Sclerodermus are small wasps that can become pestiferous and sting people when they attack wood-boring beetle larvae that have infested wooden structures and furniture.

Classification

Common name: none

Scientific name: Sclerodermus Latreille

Order: Hymenoptera (bees, wasps, ants, and kin)

Family: Bethylidae (flat wasps)

Distribution

There are approximately eighty species of Sclerodermus worldwide, three of which occur in North America: Sclerodermus carolinensis ranges from Connecticut, New York, and Illinois, south to Georgia and Louisiana; S. macrogaster ranges from Virginia, west through Arkansas and Texas, south through Central and South America, as well as Caribbean Islands; and S. ventura is known from California and possibly Hawaii.

Figure 1. Wingless female Sclerodermus. Note the relatively small size and ant-like appearance. After Skvarla (2018).

Description

Small wasps, 0.05–0.25 inches (1.5–6 mm) in length (Figure 1), with a flattened, ant-like appearance. Both sexes can be winged or wingless, although the majority are female (85– 97%) and wingless (75–99%). The head is comparatively large and boxy or squarish while the abdomen is long and tapered. Sclerodermus carolinensis (Figure 2) is light to dark red to brown, with the abdomen being slightly darker than the head and thorax. Sclerodermus macrogaster (Figure 3) is colored similarly to S. carolinensis but with light cream patches on the thorax. Sclerodermus ventura (Figure 4) is distinctly bicolored, with a light red had and thorax and dark brown abdomen.

Figures 2–4. Sclerodermus species of the United States and Canada. 2) S. carolinensis. 3) S. macrogaster. 4) S. ventura. Modified from Skvarla (2018).

Life history and behavior

The life history of North American species is largely unstudied and little is known beyond the fact that they parasitize wood-boring beetle larvae. Other species that attack wood-boring beetle larvae are well studied, particularly those in China where they have been used as biocontrol agents of longhorn beetles in lumber forests, and the following life history summary is based largely on those species.

Sclerodermus attack a number of beetle families, including longhorn beetles (Cerambycidae), metallic wood-boring beetles (Buprestidae), death-watch beetles (Anobiidae), and bark beetles (Scolytinae); they have also been recorded to attack non-beetle larvae under laboratory settings.

Female Sclerodermus are quasisocial, that is, they exhibit cooperative prey suppression and brood care and help raise each other's offspring.  Lone females typically attack smaller beetle larvae, while groups of females can tackle much larger larvae. Each female can lay 5–120 eggs per host, depending on host size and number of wasps attacking the same host.

Male Sclerodermus live for a few days to a week, while females can live for up to seven months. Female offspring are produced from fertilized eggs and male offspring from unfertilized eggs. This combination of traits allows an unmated female to rear an initial brood of male-only offspring, mate with one or more sons, and then rear a second brood of female offspring.

Medical importance

The propensity for Sclerodermus to parasitize wood-boring beetles, female-biased sex ratio, ability to reproduce sexually and asexually, and potentially large brood size can lead to the wasps becoming pestiferous when they co-infest wooden furniture or wood-framed buildings infested with wood-boring beetle larvae. When infestations are large, dozens of wasps may be seen per day when females search for new hosts. When picked up with bare fingers or accidentally trapped under or between clothing, female wasps can deliver a painful sting.

Most Sclerodermus infestations are known from Europe, particularly Italy, and attributed to S. domesticus. However, twelve other species have also been reported to sting humans in Asia, Africa, and North and Central America. Only one case of Sclerodermus infestation has been reported in the United States, although it is unclear if this is due to a lack of knowledge and reporting of the problem or if there are truly fewer infestations compared to Europe. Additionally, the related bethylid wasps Epyris californicus (Ashmead, 1893) and Cephalonomia gallicola (Ashmead, 1887) have been reported to become similarly pestiferous in the western United States.

The first sign of a Sclerodermus sting is usually a pin-prick pain which is followed by a red, itchy welt 0.04–0.2 inches (1–5 mm) in diameter. The welts generally spontaneously resolve in 5–15 days, although may last up to 30 days. Systemic symptoms include general malaise, mild fever, nausea, and dizziness lasting up to 3 days. Because the stings are accidental or defensive, they can be found on any area of the body. However, depending on where infestation is located, stings can be clustered on certain body regions. For example, if the wasps are in wooden building rafters the stings may be concentrated on the head and shoulders, but if the wasps are in an antique chair that is being repaired the stings may be concentrated on the hands and lower arms. The stings may also occur in a line if an individual wasps stings multiple times. Topical corticosteroids and systemic antihistamines can effectively treat the sting symptoms.

Control

The only way to eliminate recurring stings is identification and elimination of the Sclerodermus infestation. This is easily done when the infestation is limited to a piece of infested furniture or cabinetry that can be physically removed from the home. Beetle and wasp co-infestations are more difficult to eliminate when the wood-boring insects infest the rafters or frame of a building. Multiple applications of liquid insecticides and tenting and fumigation may be required in such circumstances. If such treatment is needed, it should be conducted by a licensed pest control operator.

This article is summarized from Skvarla (2018). See that paper for relevant citations and additional information.

Skvarla, M. J. 2018. A review of Sclerodermus (Hymenoptera: Bethylidae) infestations and repot of the first case in North America. Journal of Medical Entomology.

Authored by Michael Skvarla, Insect Identification Laboratory Director & Extension Educator, September 2017