Urodacus armatus

Scientific Name: Urodacus armatus Pocock 1888
Size: 30-60mm
Ecomorphotype: Semi - Fossorial Obligate burrower

Description: A member of the endemic Australian Urodacidae family, whose closest relatives include members of the Scorpionidae inc., Heterometrus, Opisthophthalmus, and Pandinus.

This species is relatively small, being similar in size to U. manicatus. Usually a uniform light sandy colour with dark red leg joints. Hands are robust with short fingers, similar to U. manicatus. Tarsal claws are equal length. Legs are relatively short for a desert adapted species. A sand comb is present on the front two leg patella’s. Cheliceral teeth show a lack of secondary serrations.

Sexing: Males have a slightly longer metasoma with significantly longer pectines and many more pectinal teeth, often twice that of the female. Males also display the typical Urodacid split operculum with genital papillae. Otherwise there is very little sexual dimorphism.

This inland species complex occupies a variety of soils from fine clays to coarse dune sand; in fact it is one of the least specialised Urodacus. A short burrow is constructed and often regularly blocked, especially in loose soil areas. Regular blocking would appear to help minimise evaporative water loss from the scorpion. Due to the regular blocking behaviour burrows in loose soil are often inconspicuous, so much so that when black lighting scorpions seem to appear from nowhere. This is quite a different strategy to U. yaschenkoi, which digs much deeper burrows and only blocks during periods of inactivity. This species is a sit-and-wait predator, but unusually it prefers to wander out onto the sand or climb up onto the branches and foliage of low bushes where it waits to ambush its prey. It’s not uncommon to find a number of these scorpions all occupying the same bush. They will often sit upside down just above the ground waiting for something to wander up along the vegetation they are on.

Due to occupying such a wide range of soils burrow entrances vary quite considerably. In loose soil as stated there is often no burrow entrance, in hard soils the entrance is often crescent shaped with no sign of surrounding excavated soil (see inset image with coin), intermediate soils often show a noticeable fan of excavated soil around the entrance more typical of most other Urodacus.

Probably one of the most taxonomically challenging species complexes, quite possibly none of these scorpions has ever been described as there is suggestion the holotype may have been misinterpreted or mislabeled. Regardless, at present all these typs of scorpions are lumped into the one species. No doubt there will be a number of species in this complex as there is much variability across its range.

Reference:

Koch, L. E. 1977. The taxonomy, geographic distribution and evolutionary radiation of Australo-Papuan scorpions. Records of the Western Australian Museum 5 (2):83-367.