blotchwing spider wasp

Blotchwing spider wasp is a medium-sized wasp but a small wasp. It occurs in western Europe and eastern North America. Adults are slender, black and red, and ¼″ to ⅜″ long. Females are larger than males.

The head is wider than long and entirely black. There are two large compound eyes on the side of the head and three small simple eyes in a triangle on the top. The compound eyes strongly converge at the top. The antennae are thread-like and black. On the female they have 12 segments, on the male they have 13 segments. The tips of the mandibles are reddish.

The thorax has three segments. The exoskeletal plate covering upper part of the first segment (pronotum) is relatively short but extends to the bases of the wings. It is more or less triangular when viewed from the side, more or less horseshoe-shaped when viewed from above. The front is perpendicular to the upper surface. The second segment has a line-like groove (suture) across the side (mesopleuron).

The first two segments of the abdomen and the basal portion of the third segment are brownish-red. The remainder is black. On the female, there is a short ovipositor at the tip of the last segment. The ovipositor also functions as a sting.

The legs are long, slender, and mostly black. The second segment (trochanter) of each leg is complete, not divided into two segments. There is a pair of spines at the tip of the fourth segment (tibia) of the middle and rear legs. The spines on the hind leg are of equal length. The third segment (femur) and tibia on the hind leg are brownish-red. The femurs on all legs are covered with short, silvery hairs. The tibiae on the hind leg is toothed on the upper side.

The wings are clear. The female has a dark spot near the tip of each forewing.

Total length: ¼″ to ⅜″

Woodland edges and openings

Late spring to early Autumn

Adults are often found on flowers.

The female wasp preys on spiders that are immature but usually larger, sometimes five or six times the mass, of the wasp. When she catches a spider she stings it first between the fangs to immobilize these weapons, then in the body to paralyze the prey. She hangs it from a low twig using silk from the spinnerets of the captured prey. She then excavates a burrow in sandy soil, returning repeatedly to the prey to protect it from scavengers and to ensure that it is still paralyzed. The burrow is diagonal, about to 1½″ deep, and has a ⅜″ long cell at the bottom. Once that is completed, she drags the spider into the cell, deposits a single egg, and covers the burrow. When the egg hatches, the larva affixes itself to the upper surface of the host spider and feeds from the outside.

Immature orb weaver spiders, including bordered orbweaver (Larinioides patagiatus), humpbacked orbweaver (Eustala anastera), marbled orbweaver (Araneus marmoreus), starbellied orbweaver (Acanthepeira stellata), and at least one species of Neoscona.

Sources

24, 27, 29, 30, 82.

Location: Kasota, MN

We have several hundred of these wasps, ground nesting/hatching in one of our gardens.  I do routine garden work there, and we walk through them buzzing around our sidewalk frequently, with no issues.  They are very passive (non-agressive) and have not stung anyone in the several summers that we have had them here on our property.  We are well south of the range that is shown for this species.   

Location: Woodbury, MN

Looks aggressive !