Drain holes make perfect entry points for grass-carrying wasps to access window tracks for nest construction, but sometimes it’s hard to get the grass completely inside.
During the waning days of autumn, as the hours of daylight grow ever shorter, I perform the semiannual task of washing my windows in a desperate attempt to maximize the entry of every photon of sunlight into my home. Part of this autumnal ritual involves sliding window screens along their tracks to expose the obstructed window panes in preparation for a wash-down. Last week as I moved the screens, I noticed tiny hay mounds lining the tracks in which the screens run. What manner of mischief was this? Were the grassy mounds windblown lawn clippings or perhaps the bedding of diminutive window fairies?
Upon closer inspection, small papery cocoons confirmed the presence of one of the most curious members of the thread-wasted wasp clan, grass-carrying wasps belonging to the genus Isodontia. We met other members of the sphecid wasp clan, such as the cicada killer and steel blue cricket hunter, in previous episodes of Bug of the Week. In nature, grass-carrying wasps typically line abandoned beetle galleries or crevices in trees with blades of grass to create nests for their young. However, storm windows provide excellent opportunities for nest building by virtue of their hollow tracks. Within their grass encased cocoons, wasp pupae endure the cold of winter and await the warmth of spring when they complete development and emerge as adult wasps.
Summer is spent finding mates, feeding on nectar and pollen, and constructing grass-lined brood cells with blades of grass from nearby meadows and lawns. Once the grassy cells are prepared, the female wasp will capture, sting, and paralyze tree cricket or katydids, carry them back to the gallery, and deposits eggs on the victims. From the eggs hatch legless larvae which consume the hapless prey. Scientists have discovered that larger numbers of prey in each cell result in the production of larger wasps. Upon completing their juvenile development, each larva will make a papery cocoon and transform into a pupa. In the mid-Atlantic region, grass-carrying wasps may complete two generations each year.
There is no need to harm these interesting wasps or treat them with pesticides, as they are totally uninterested in harming humans. As you will see from the video, I was able to observe and film these interesting wasps at close range without harm.
The interesting article “Sex allocation, nests, and prey in the grass-carrying wasp Isodontia mexicana (Saussure)(Hymenoptera: Sphecidae)” by K.M. O’Neill and R. P. O’Neill was used as a reference for this episode, as was the delightful web posting created by Steve Jacobs referenced below: