I found some interesting mud constructions the other day. They were tucked away in a crack in a piece of 4x4 lumber that had been sitting on the ground. They were perfectly arranged so that they could fit in the crack if they were placed alternately.
Almost any mud construction attached to rocks, trees, walls or other objects belongs to a wasp or bee. There are a few ground beetles that build mud cells for their eggs, but you are unlikely to come across them.
Some common mud dauber wasps build a series of nest cells close together, then cover the whole thing with a shapeless mass of mud. The well-known organ pipe mud dauber builds a series of mud tubes, divided into rooms inside so each larva has its own space. The potter wasp makes tiny, perfect pots that could cause one to think they were made by fairies. Other wasps and solitary bees attach mud nests to twigs or place them inside cavities.
Journal photo by Claire Stuart
Some common mud dauber wasps build a series of nest cells close together, then cover the whole thing with a shapeless mass of mud.
The constructions I found are mud nest cells built by certain spider wasps to hold their eggs and food for their larvae. The spider wasp family Pompilidae is a large one, including many solitary wasps whose larvae eat spiders. In general, each genus specializes in spiders of a size that they are able to handle, although the spiders are often larger than the wasps. In the southwestern states, there are spider wasps that hunt tarantulas and huge trapdoor spiders.
Spider wasps do not kill spiders. They paralyze them with a sting, then drag them into a burrow or a mud cell. One egg is laid on the spider and the egg is sealed into the chamber and left to hatch. A dead spider would dry out and not provide nourishing food. The larva will eat the paralyzed spider, leaving the vital organs until last so that the spider will live long enough for the larva to mature. The larva will then spin a cocoon, become an adult and dig its way out.
The particular mud cells that I found are probably those of wasps in the genus Auplopus, known for making thimble-shaped mud nests, each holding one spider and one egg. These wasps are usually found in the woods, but they sometimes enter old buildings where they can find cracks in which to place their nests. Sometimes they build in abandoned nests of other types of wasps and sometimes under bark and rocks or in crevices.
Auplopus wasps usually specialize in capturing spiders in the Family Anyphaenidae. These are common, light-colored and rather small ground-dwelling spiders that wander around on soil and plants.
Our local spider wasps are about half an inch long, usually black with dark wings, sometimes with orange legs or small orange markings. They are extremely long-legged. They appear to be very nervous because they are usually seen walking quickly around on the ground or on tree trunks, jerking their wings and tapping their antennae as they track spiders.
Adult wasps do not eat spiders. They visit flowers and feed on nectar. They are solitary, with each female working by herself. Males have nothing to do with catching spiders or nest building. They simply set up territories where they perch and watch for females to mate.
Female spider wasps show a bit of intelligence because they are able to learn from experience. Over her lifetime, a wasp's hunting abilities improve and she is able to find and overcome spiders faster and more efficiently.
Spider wasps are not at all aggressive and will not sting unless they are seriously threatened or harmed. It is perfectly safe to watch them if you happen to see one at work.
Although few insects are around at this time of year, you can always find signs of insect life if you are a careful observer.
- Send your insect questions to Claire Stuart by e-mail at email@example.com or write her (with self-addressed stamped envelope) in care of Living Section, The Journal, 207 W. King Street, Martinsburg, WV 25401.