Thread-waisted wasp

IUCN Red List

not listed

NatureServe

not listed

Minnesota

not listed

Ammophila pictipennis is a medium-sized, solitary, ground-nesting, thread-waisted wasp. It occurs in the United States east of the Great Plains, in southern Ontario Canada, and in eastern Mexico. Adults are found from June to October in fields. They feed on flower nectar. Larvae feed on larvae of owlet moths, especially cutworms, including armyworm, lesser black-letter dart, yellow-striped armyworm, and corn earworm.

Adults are ¾″ to 1″ (20 to 25 mm) in length. The base of the abdomen is contracted into a thin stalk, making the body appear “thread-waisted”. This is the feature that gives the family Sphecidae its common name.

The head is dull black. There are two large compound eyes, one on each side of the head; and three small simple eyes (ocelli) in a triangular pattern at the top of the head between the compound eyes. The antennae are thread-like, black, and about as long as the head and thorax combined. They are not elbowed.

The thorax (mesosoma) is entirely dull black, with no silver markings. It has three segments, but the first segment of the abdomen is fused to the thorax, giving the thorax the appearance of having four segments. The upper plate on the first segment (pronotum) is short and collar-like. There is a short, rounded lobe on each side of the pronotum that does not reach the plate at the base of the wings (tegula).

The abdomen consists of a large first segment (propodeum) that is fused to the thorax; a relatively long, narrow, stalk-like second segment (petiole); and the bulbous remainder (gaster). The gaster is bent downward at the end of the petiole. The rear part of the petiole and the first two segments of the gaster are orange. The remainder of the gaster is dull black.

The wings are orange on the basal half, grading to black on the rear half. As the wasp ages, the black area gradually fades to orange. The forewing has three submarginal cells. There are two lobes at the base of the hindwing. The inner lobe (vannal lobe) is large.

The legs are long, slender, and black. The fourth segment (tibia) on the middle leg has two spurs at the tip.

Size

¾″ to 1″ (20 to 25 mm)

Similar Species

Fields

Season

June to October

Behavior

Adults will sometimes grip the stalk of a plant at night and hold its body out at right angles to the stem.

The wings are held over the body when at rest.

Life Cycle

The female digs a nest with a single cell in sand, provisions it with a single paralyzed caterpillar, and lays a single egg.

Larva Food/Hosts

Larvae of owlet moths (family Noctuidae), especially cutworms, including armyworm, lesser black-letter dart, yellow-striped armyworm, and corn earworm.

Adult Food

Flower nectar