Spider Wasp - Morphology

Morphology

Like other strong fliers, the thorax of Pompilidae is modified for efficient flight. The metathorax is solidly fused to the pronotum and metathorax; moreover, the prothorax is best developed in families such as Pompilidae and Scoliidae because they use their forelegs to dig.

Pompilids typically have a slender body with long, spiny legs and the hind femur is often long enough to reach past the tip of the abdomen. The tibiae of the rear legs usually have a conspicuous spine at their distal end. The first two segments of the abdomen being narrowed characterize the slender look of their bodies. The pompilid body is typically dark (black or blue, sometimes with metallic reflections), but many brightly colored species exist. From a lateral view, its pronotum looks rectangular and it extends back to the tegulae, near the base of the wings. Most species are macropterous (having long wings), but a few brachypterous (short-winged) and apterous (no wings) species are known.

Spider wasps are best distinguished from other vespoid wasps in having (in most species) a transverse groove dividing the mesopleuron (the mesepisternal sclerite, a region on the side of middle segment of the thorax above the point where the legs join) into halves. Like other Vespoidea, they have antennae with 10 flagellomeres in the female and 11 in the male. Most Pompilidae have the inner margin of the eye straight. The hind wings do not have a distinct claval lobe, but they have a distinctive jugal lobe. The hind leg has a tibial spur with a tuft or row of fine hairs. The legs are long and slender with the tips of the tibia (metatibia) long enough to extend beyond the tip of the abdomen (metasoma). Sexual dimorphism is not marked, although females are often larger than the males, with coloring and wing appearance varying greatly among the many species, though black is the most common color, with contrasting aposematic markings of orange, red, yellow, or white also being fairly common. Larvae can also be identified by physical examination.

Spider wasps are long-legged, solitary wasps that use a single spider as a host for feeding their larvae. They paralyze the spider with a venomous stinger. Once paralyzed, the spider is dragged to where a nest will be built – some wasps having already made a nest. A single egg is laid on the abdomen of the spider, and the nest or burrow is closed.

The size of the host can influence whether the wasp's egg that will develop as a male or a female; larger prey yield the (larger) females. A complex set of adult behavior can then occur, such as spreading soil or inspecting the area, leaving the nest site inconspicuous. When the wasp larva hatches, it begins to feed on the still-living spider. After consuming the edible parts of the spider, the larva spins a silk cocoon and pupates, usually emerging as an adult the next summer. Some ceropalines lay the egg on a still-active spider, where it feeds externally on hemolymph. In time, that spider will die, and the mature wasp larva will then pupate.