American Sand Wasp

If you, like me, enjoy a visit to the local river, then you have probably encountered the beautiful American Sand Wasp. The ASW is commonly found along rivers, streams and other areas that feature sandy/loamy soil, sand dunes, and other areas of loose sandy soils. They are nearly an inch in length, with a distinct black and white banded abdomen, green eyes (that may look blue or blue-gray in certain light), clear wings with dark veins, and mostly yellow legs. The head and thorax are covered in short white hair.

Females are gregarious nesters, meaning they will often nest in the same area as other females. These areas may include the nesting sites of as many as fifty females and are used year after year. Females begin excavating a nest by scraping soil with their front legs and passing it underneath their bodies. Once the shallow nest is dug, the female will tamp down the soil mounded up around the entrance in an attempt to hide the opening. Each nest may contain one to three chambers. At this time, the female begins looking for prey to provision her offspring with. They prey almost entirely on flies, including houseflies, deer flies, and even mosquitoes. She will sting the fly to paralyze it and then carry it held tightly to her body and fly back to the nest. By using subtle landscape markers, she can consistently locate her nest, whereas by comparison we humans struggle to locate our car! Once inside the chamber, the female will lay a single egg on the paralyzed fly. The newly hatched wasp larva will feed on the fresh meat so lovingly provided by its mother. The female participates in progressive feeding, meaning she will continue to capture and provide prey for her developing larvae until they pupate. She may also shift between progressive feeding, and mass feeding, meaning she may also provide numerous paralyzed fly dinners at once for her larvae. When those meals have been consumed, she will continue to provide food. Each larva may consume up to twenty-four fly dinners before forming a pupa. If she has formed three chambers, with three separate larvae, that is seventy-five fly dinners provided to hungry wasp larvae!

Once the wasp larvae have pupated, the female will close that chamber and excavate an additional chamber within the nest and provision it with fly prey for the second generation of wasp larvae. Occasionally she will close off the nest entirely and dig a completely new nest nearby. Most of their adult life is spent nest building, nest provisioning, and hunting for prey for developing larvae. If one were to do the math and calculate how many nesting females are at a given nesting aggregation, and every female capable of double broods each season, and they may form and maintain up to three chambers within each nest, it is conceivable they would capture, kill and feed their offspring more than 5,000 flies! Talk about biological control!!

Males will emerge from the nesting chambers first and spend several days flying rapidly and erratically over the ground above the aggregation area. Occasionally they will land and use their feet to sense vibrations under the soil, signifying females moving around underground. Males may also be able to use their antennae to pick up the subtle pheromones emitted by emerging females. Within a few days of the male’s arrival, the females emerge, and the melee begins! Males may pounce on virgin females as soon as they leave the nesting chamber, or if the females manage to take flight, a male gives chase and tries to win the female's favor. If she is receptive, the pair will quickly leave the chaos ensuing around the aggregation site and set off alone for mating. If by some chance they are knocked to the ground, another male still in the area may force the breeding male away from his female and take over breeding rights.

Like nearly all animals in nature, there are other animals preying on them, and these wasps are no different. Many flies, in a form of turning-the-tables on your enemy, prey on these wasps. Satellite flies, cuckoo flies and others all prey on sand wasps. The observant fly waits for a passing sand wasp and will follow the wasp to the opening of the nesting site. Once the fly is inside the larval chamber, it will lay an egg on the wasp larva or on the provisioned prey brought in by the female wasp. It is believed by many wasp experts that the female is instinctually programmed to over-provide for her offspring to give a higher chance of survival to her progeny. It has been observed by scientists that the fly predator and the wasp larva can and have developed side-by-side in the nest to adulthood, much to the chagrin of the female wasp. She has unwittingly become the provider for her own offspring as well as to the fly who would just as soon eat her young. Such deception!

These busy little wasps are solitary and not known to be aggressive in any way toward humans, pets or livestock. Occasionally they set up nesting aggregations near ball parks, playgrounds and other areas where children and families are known to be. Control measures are not recommended, since they pose no real threat to people. It is best to stay away from those areas for four to six weeks which will allow these wasps to finish their lifecycle. As humans, a little tolerance goes a long way, and if we just remind ourselves these pretty little wasps are killing thousands of potentially dangerous and definitely pesky flies and mosquitoes, making our life much healthier and our outdoor time more enjoyable.