square-headed wasp

not listed

not listed

not listed

Ectemnius maculosus is a small square-headed wasp. It occurs in the United States east of the Great Plains and across southern Canada.

Adults are ⅜″ (10 mm) in length and black with yellow markings.

The head is large, square, and black. There are two large compound eyes on the sides of the head and three small simple eyes (ocelli) in a triangle on top of the head. The shape of the triangle is low, meaning the sides are shorter than the base. There is a longitudinal ridge in front of the ocelli and a transverse ridge behind the compound eyes. The compound eyes do not have a sharp groove (fovea) on the inner margin. On males, the back of the head is distinctly narrowed behind the compound eyes. The upper part of the forehead (frons) is evenly pitted (punctate). The plate on the face (clypeus) has a large, polished, extension (bevel) on the upper margin. It is entirely black on both sexes. The jaws (mandibles) are mostly yellow above, black just near the tip, and are entirely black below.

The antennae rise low in the face. They consist of a long basal segment (scape), a short connecting segment (pedicel), and a whip-like end section (flagellum) with several segments (flagellomeres). The scape is yellow, the pedicel and flagellum are brown. The first flagellomere is more than twice as long as wide. The second flagellomere is depressed on the underside near the base.

The thorax is black and has three segments, the prothorax, mesothorax, and metathorax. However, the first segment of the abdomen (propodeum) is fused to the thorax, giving the thorax the appearance of having four segments. The upper plate on the prothorax (pronotum) is short and collar-like. It extends rearward on the sides to the plate at the base of each wing (tegula). It appears horseshoe-shaped when viewed from above, triangular when viewed from the side. It is mostly black except for a yellow band on the front margin of the upper surface. The band is interrupted in the middle. On the mesothorax, the large front plate (mesoscutum or scutum) is black with no yellow markings. It has transverse microridging in front and longitudinal microridging in the rear. The smaller rear plate (scutellum) has a pair of narrowly separated, yellow spots. The upper surface of the metathorax (metanotum) is entirely black, with no yellow markings. On the lower front of each side of the thorax there is a small yellow spot.

On the rear part of the body the second through fifth segments (tergites) have a pair of narrow, widely separated spots on the front margin. On the fifth tergite the spots are even more widely separated.

The wings are tinted brown. On the forewing there is a single submarginal cell. The recurrent vein ends in the outer third of the submarginal cell.

On all legs the third segment (femur) is black, the fourth segment (tibia) is yellow, and the last part of the leg (tarsus), corresponding to the foot, is yellow. On the front legs the femur has a sharp, rearward-pointing spur near the middle. It does not have a sharp ridge or tooth on the underside near the base.

⅜″ (10 mm)

The nest is usually built in pithy stems. It is provisioned with paralyzed adult flies.

Flies

Flower nectar

Sources

29, 30, 82, 83.

This species has no common name. The name of the subfamily Crabroninae is square-headed wasps, and it is adopted here for convenience.

Location: Slinger, Wisconsin