"Giant wasps have invaded my landscape! They’re digging holes in my landscape beds–and, they are really large wasps!"
During July and August, the Master Gardener Hotline gets several calls from excited (and very nervous) homeowners about large wasps flying. They are describing a wasp known as the cicada killer wasp (Sphecius speciosus). The cicada killer wasp is the largest wasp that occurs in our area.
The cicada killer is quite large, up to 1½ inches in length, with a black or dark brown body and yellow band markings around the abdomen. The head and thorax are a dark rusty red and the wings are amber.
Although quite menacing in appearance, this large wasp is actually a beneficial insect useful in the control of the noisy cicadas that also appear in July and August each year. The male cicada killer wasp may demonstrate aggressive-like behavior, darting back and forth, diving at people nearby and sometimes flying into windows. Fortunately, the male cannot sting.
The female can sting, but is not usually aggressive toward people. She is often seen burrowing in the ground or in flight carrying the preferred victim of her powerful sting - a paralyzed cicada.
The cicada killer is a solitary wasp, but several wasps and nests can often be found in the same immediate vicinity. The female cicada killer will dig a tunnel about ½ inch wide and 6-to-10 inches long, with several side chambers, in loose soil or sandy embankments. She may also be found burrowing between cracks on the sidewalk or driveway.
Once the tunnel and chambers are dug, female cicada killers then fly, glide or drag the cicadas back to their nests to provide a food source for the larvae when the egg hatches. Then the tunnel is sealed. Little piles of soil mark the entrances to the nests, perhaps making quite a mess of a lawn or flower bed.
After an egg hatches, the larva feeds on the cicada or cicadas that a female has provided for her young. The larva develops through several molts (instars) before pupating inside a woven, spindle-shaped brown case measuring up to 1¼ inches long.
Winter is spent in the larval or pupal stage. Adults emerge in the summer, feed, mate and produce new nesting burrows. One generation occurs per year. While larvae feed only on cicadas, the adults will feed on flower nectar.
Since the cicada killer wasp is a beneficial insect whose aboveground activity is limited to only a few months when cicadas are active, control is not necessary in most cases. However, if you have several of these insects, year after year, you may want to discourage them from coming to your yard, especially if children play in the area.
You can try blocking nesting activity with weed blocking fabric covered with mulch in flower beds where digging occurs. Applying up to a tablespoon of carbaryl dust insecticide in the tunnel burrowed by the wasp might also be helpful. In cases where cicada killers nest in turfgrass areas, a healthy thick lawn is always a deterrent.
Beneficials in the Garden & Landscape is an Earth-KindTM program coordinated through Extension Horticulture at Texas A&M University. Earth-Kind uses research-proven techniques to provide maximum gardening and landscape enjoyment while preserving and protecting our environment.
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