Mason wasp

Description

There are 30 species of mason wasps in the genus Zethus. Only six occur in North America north of Mexico. Five of these are restricted to the southernmost states. Only one species, Zethus spinipes, occurs in Minnesota. There are two subspecies of Zethus spinipes, but only one subspecies occurs in Minnesota.

Zethus spinipes ssp. spinipes is a common, solitary, mason wasp. It occurs in the northern United States east of the Great Plains and in southern Ontario Canada. It is uncommon in Minnesota.

Adults are small and black with just a few ivory markings. The front part of the body (mesosoma) is connected to the rear part (metasoma) by narrow waist (petiole). Females have a ½″ to 9⁄16″ (12 to 14 mm) forewing length. Males are smaller, with a ⅜″ to 7⁄16″ (9.5 to 11 mm) forewing length.

The head is 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. On the male they have just 12 segments, are jointed (elbowed), and the long first segment (scape) is ivory on the underside. On the female they have 13 segments, are not elbowed, and are entirely black. On both sexes there is a ivory spot on the head at the base of each antenna. The spot is small but distinct on the male, much smaller on the female. The cheek (gena) tapers nearly to a point at the bottom. The jaws (mandibles) are long and knife-like. The plate on the face (clypeus) is pale ivory on the male, black on the female. The bottom margin of the clypeus is more or less straight. It does not extend below the level of the lower margin of the compound eye.

The thorax is black and has three segments. However, 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, collar-like, and entirely black. The plate at the base of each wing (tegula) is black and long, twice as long as wide. The second segment of the thorax (scutum), by far the largest, is entirely black on both sexes. On the male the third segment has a pair of ivory spots. On the female it is entirely black. The first and second abdominal segments form a petiole that connect the abdomen to the thorax.

The first segment of the metasoma is twice as long as wide and only half as wide as the second segment. It is black with a ivory band at the end. The second segment is larger than the remaining segments combined. It is constricted at the base into a second petiole. The constricted portion is no more than half as wide as the first segment. Zethus is one of only two genera in the family Eumeninae that have a narrowly contracted (petiolate) first segment of the mesosoma. There is a narrow ivory band at the end of the second segment.

The wings are smoky brown. On the forewing, the first discoidal cell is very long, about half the total length of the wing. The first subdiscal cell (sd) does not touch the marginal cell (m). There are three submarginal cells. At the base of the second submarginal cell there are two distinct kinks, forming a dogleg in the M vein.

The legs are black. The fourth segment (tibia) of the middle leg has a single spur at the tip. The last part of the leg (tarsus), corresponding to the foot, has five segments. There is a pair of claws at the tip of each tarsus. The claws are split (cleft) at the end.

Size

Female forewing length: ½″ to 9⁄16″ (12 to 14 mm)

Male forewing length: ⅜″ to 7⁄16″ (9.5 to 11 mm)

Similar Species

Habitat

Ecology

Season

Behavior

When at rest, the wings are folded longitudinally over the body.

Life Cycle

The female may nest in an abandoned burrow of another insect, or build a nest from vegetable matter and resin. It does not create a clay “pot”.

Larva Food/Hosts

Adult Food