This species is monotypic.
Typically 10-20 mm, most are around 15 mm.
The genus Arachnospila is most similar to Anoplius, but they lack strong bristles on the pygidium. However, of all of the genera split from Pompilus, Arachnospila is perhaps the most closely related to Anoplius.
This species is very similar to A. scelesta, but is practically hairless. A. scelesta is rather hairy, particularly on the antennal scape (large segment closest to the face).
All of the Arachnospila have strong tarsal and pulvillar combs.
Transcontinental in most of the United States, rare in the extreme south.
Nests in sandy or gravelly areas but will venture far from nesting areas in search of prey and flowers (often taken on flowers of Daucus carota and Solidago spp.).
Mid-summer to early autumn.
Adults take nectar from flowers and may drink fluids from their spider prey (personal obs.). Females provision nests with various Lycosids.
An observation of nesting behavior of Arachnospila arcta-Nick Fensler
At 1622 on 31 August 2006 a female Arachnospila arcta was observed dragging a Lycosid across and abandoned sand volleyball court in Pandora, Putnam County, Ohio.
The wasp stopped, let go of the spider, circled the area to orient, and walked approximately 18 cm away from it. It then tilted its body at approximately a 45 degree angle and began to dig, removing sand with its forelegs, and occasionally pulling it away from this original hole with both the fore- and middle legs. During construction it would occasionally stop and check on the spider (eight times), circling it and touching it with its antennae and mouthparts, and would also drive away any ants in the area. On two occasions it re-stung the spider in the region of the cephalothorax and on a third the spider almost completely recovered and a chase and grappling ensued.
The wasp took approximately 65 minutes to complete its burrow. The wasp then grasped the spider by the second leg near the trochanter and dragged it to the burrow opening. The wasp positioned the spider over the burrow and then grasped it by the spinnerets and backed into the burrow. After 22 minutes the wasp emerged and was collected. I then carefully excavated the burrow. The opening was approximately 8 mm wide and was semi-circular in shape. The burrow was approximately 7 cm long, straight, and oblique with a widened terminal cell.
The spider was removed but the egg could not be found and may have been jarred from the spider during my excavation.