Anuroctonus phaiodactylus

(Wood, 1863)

Today's subject is Anuroctonus phaiodactylus (Wood, 1863). The generic name, Anuroctonus, is from the Greek word an, meaning "not," and the name Uroctonus, a genus of scorpion from North America. Anuroctonus thus means "not Uroctonus." The specific name, phaiodactylus, is from the Greek words phaeo, meaning "dusky," and dactyl, meaning "finger," and refers to the dark coloration of the fingers of the claw.

Anuroctonus phaiodactylus
Vital Stats:
  • SIZE: < 65 mm
  • ECOMORPHOTYPE: Fossorial
  • DEFENSE: Strikes defensive posture with outstretched pedipalps and forward-oriented stinger.
  • FOOD: Small arthropods.

This scorpion is in the family Iuridae. Anuroctonus contains only one species. However, I think we may actually be dealing with a complex of morphologically indistinguishable species across the range of the genus.

Original Description: Wood, H. C. 1863

Descriptions of new species of North American Pedipalpi. Proceedings of the Academy of Natural Sciences of Philadelphia, 1863: 107-112. This species was originally described by Wood (1863) as Centrurus phaiodactylus. The species was later transfered to Uroctonus, before being placed in Anuroctonus.


This species occurs in northwestern Baja California in Mexico, and in southern California, Arizona, southern Nevada, western Utah and southeastern Idaho in the United States. I have also seen one specimen collected from New Mexico, but could not subsequently locate the record for confirmation. Older records also list Colorado, Virginia, and Guatemala in distribution records for Anuroctonus phaiodactylus. These are probably incorrect. In southern California, I find this scorpion in well-packed sedimentary soils, usually, but not always, on sloping ground, especially near the bases of hills. On Stansbury Island, on the Great Salt Lake in Utah, I found this species in gently sloping to flat areas of packed, sandy soil. In Idaho, this species occurs on gently sloping grassland at an elevation of 4000 feet [Anderson, 1975, Tebiwa, 18(1):1-17]. In all cases, the scorpions are associated with packed soils and some sort of vegetation. Loose sand and completely barren ground do not seem to be desirable.

Anuroctonus phaiodactylus map
Fun Facts

This species spends almost its entire life inside its burrow. Every scorpion constructs a burrow and there is only one scorpion per burrow. Unlike some scorpions, which emerge from their burrows to ambush prey, Anuroctonus waits within its burrow for hapless prey to enter. Because the stinger cannot be brought to bear within the confines of the burrow, the relatively large, powerful pedipalps, or claws, are the primary means of subduing prey. Anuroctonus phaiodactylus can be very abundant in the areas where it occurs. Ordinarily, several scorpions are found in the same general area. The burrow openings are readily visible on the soil surface and are oval or cresent-shaped. Once a search pattern is developed for the burrow entrance, entire colonies of Anuroctonus are easily discovered. Only adult males leave the burrow for long periods. This occurs when they go in search of mates. As a result, nearly all of the Anuroctonus collected by blacklighting or in a casual fashion are adult males. To collect females, one must excavate the scorpion's burrow. A military-style entrenching tool is very handy for this type of work.

  1. Mark the burrow by carefully inserting a long, flexible grass stem or similar object into the burrow and working it down as far as possible. The tunnel may twist and turn as it spirals down, so this is not always an easy task. The grass stem will allow you to track the path of the burrow, even if it becomes obscurred by your digging.
  2. Dig a wide, 6-to-12-inch-deep hole on the down-hill side of the burrow, six inches or so from the burrow entrance. It is important that this digging not disturb the burrow. This hole will give you some working room and will receive the soil you excavate from directly around the burrow.
  3. CAREFULLY, GENTLY remove the soil along the upper reaches of the burrow so that the grass stem is visible. Always remove the soil from the down-hill side of the burrow, essentially removing the floor of the tunnel. This will keep soil from filling the tunnel and when you reach the scorpion, it will drop right into your excavation hole. Don't hack in this area unless you like your scorpion in pieces. Also, too much force can easily pack the loose soil into the scorpion's burrow, crushing it.
  4. Continue to gently feed the grass stem into the burrow tunnel. Dig your excavation hole down another 6 to 12 inches and keep it cleared of soil. Work slowly and carefully--don't rush.
  5. Repeat the above steps until you reach the nest chamber and recover the scorpion!

Disclaimer: The views expressed here are mine alone and do not represent the views of the Department of the Army or the Smithsonian Institution... or anybody else for that matter. - Dr. Scott A. Stockwell

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