Many late summer bloomers such as milkweed and goldenrod are in full glory and attracting scads of insects. Among the most interesting and beautiful batch of
visitors are thread-wasted wasps in the family Sphecidae. We met another sphecid wasp, the giant cicada killer, in a previous episode of Bug of the Week. The more demure thread-wasted wasps share much with their rambunctious cicada-killing kin. Cicada killers and most thread-wasted wasps are hunters. These svelte creatures seek caterpillars, grasshoppers, spiders, and other small arthropods to serve as food for their larvae. To find and subdue prey requires a lot of energy and frequent trips to flowers for energy-rich nectar is a regular daily activity.
Flowers may also be home for their prey. Some thread-wasted wasps such as Eremnophila aureonotata and Ammophila pictipennis hunt caterpillars and upon encountering their victim deliver a paralyzing sting. These digger wasps prepare a subterranean nursery by excavating a burrow and depositing a caterpillar within. Then each wasp lays an egg on its victim. Eggs hatch into a larva that consumes the living but helpless prey. Before leaving her young, the mother carefully arranges pebbles and dirt to disguise the entry to her nest. This is probably a way to keep other insects from making a meal of her young. Have you ever wondered what insects do at night? Well, some species of thread-wasted wasps have the interesting habit of clamping their jaws on a flower or stem of a plant and hanging suspended by only their mouthparts overnight. Was this the inspiration for carnival performers to hang from a rope by their teeth, perhaps?
Other members of the thread-wasted wasps are masterful masons known to most of us as mud daubers. These sphecids locate mud of just the right consistency and roll it into tiny balls. One by one the dauber carries each ball to a protected structure like a rock ledge or cornice of a building and molds the mire into chambers for the wasp’s young. These creations may resemble a series of connected organ pipes or, when plastered over uniformly, appear as large irregular globes. As with the digger wasps, prior to laying eggs the female provisions the chambers with several paralyzed victims like spiders. Within each “pipe” of the organ are many brood chambers each with a wasp larva. Once a nest is completed and sealed, the female wasp flies away to find more mud and repeat the process again. In an interesting twist to our mud dauber story, workers cleaning up a nuclear waste facility apparently found wasps gathering radioactive soil to build their nests and many of their creations were “fairly highly contaminated” with radioactive isotopes. Just imagine giant mutated wasps glowing in the dark capturing small pets instead of spiders to provision their nests – sounds like reasonable grist for an episode of the Simpsons.
We thank Bonnie and Randy Taylor for sharing their mud daubers for this episode. Interesting and entertaining accounts of thread-wasted wasps including “The habits of aculeate Hymenoptera” by William Ashmead, “Sleep in insects: An ecological study” by Phil and Nellie Ray and “Insects: Their natural history and diversity” by Stephen Marshall were used as references. To learn more about thread wasted wasps and their radioactive creations, please visit the following web sites.