Last weekend I performed my semi-annual task of washing windows inside and out 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. During this adventure 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-waisted wasp clan, grass-carrying wasps belonging to the genus Isodontia.
We met other members of the sphecid wasp clan, such as the cicada killer, blue winged digger wasp, great black wasp, 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 deposit eggs on the victims. From the eggs hatch grub-like, legless larvae that 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 brownish colored, papery cocoon and transform into a pupa within its sheltering confines. 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.
Persistence pays off for a grass-carrying wasp as she drags an unusually long piece of grass through a drain hole into the nest. With the grass safely inside, out she goes to gather more.
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: