So this is a project I’ve wanted to do for a while but was extremely daunted by. the task. Identifying US native scorpions is hard, a lot of literature on the subject is out of date and there are precious few knowledgeable people that are working on the subject. To make matters harder for me, I wanted to aim this guide at the layman naturalist, someone who was going to look at surface level identification features but not know or care what trichobothria patterns were. As such, I’d like to write a disclaimer and say this guide is for entertainment purposes only. I have excluded many, many species from it and chose to only focus on scorpions I thought were common, readily identifiable, or interesting. I also excluded subspecies, and intentionally picked examples for the pictures I thought were the most obvious or distinct. Some scorpions in the US are medically significant, and anyone can have an allergic reaction to a sting, so caution must be taken when identifying. I also took most of these pictures off inaturalist or bugguide, but I will supply some of my own pictures here when applicable. Family organization is based on the classification currently up on TheScorpionFiles, but taxonomy is subject to change so that's another disclaimer.
Without further ado, let’s talk about scorpions.
The US is a treasure trove of scorpion activity. We are home to 7 unique families of scorpions, some of which are only found in the US and Mexico. The southwestern United States is one of the most diverse and populated scorpion hot spots in the world. Despite this variety, most people don’t pay much attention to the scorpions they live alongside. Aside from a few standout examples (Arizona Bark Scorpion, Desert Hairy Scorpion) US native scorpions are almost entirely unknown. I wanted to make this guide to introduce people who didn’t know much about scorpions to some of the diversity the US has to offer, as well as be a basic primer to scorpion identification and morphology.
So first things first, some basic scorpion biology.
Some important things to note in this diagram is the chela refers to the wide part of the pincers not including either the fixed or movable finger. The hand refers to the chela plus the fixed finger, with the movable finger connecting to the hand. Similarly, the aculeus refers to just the stinger, and the vesicle refers to just the venom bulb before the stinger. The telson refers to the aculeus plus the vesicle. The telson sometimes includes a subaculeur tooth, which looks like a second, smaller stinger on the vesicle. This can be an important diagnostic feature. I will informally refer to a scorpion's “claw”, “body”, and “tail” to make things easier. Another important diagnostic feature is the presence of granulation, which are distinct bumps on a scorpion carapace that makes it look granular or rough. Sometimes the granulation can be in a distinct line, which is called a carinae. There are smooth carinae too, which are just raised distinct lines without granulation, but I won’t be talking about those in this guide. This guide is primarily going to focus on features you can easily see without flipping a scorpion over or using a microscope, so although I highly recommend you look into scorpion biology I won’t go into too much here.
The Scorpions
Anuroctonidae
Two large “humps” on the prosoma
Noticeably darker fingers
Swollen stinger, more prominent in males
Median eyes close together and on a raised darkened hump, almost giving the appearance of having one median eye
Buthidae
Thin claws
Long, thin tail (markedly longer in males)
Front of prosoma has a slight “v” shape
Chactidae
Distinct “v” in front edge of the prosoma
Diplocentridae
Distinct subaculear tooth
Distinctly shiny
Little to no granulation
Distinct “v” shape in front edge of prosoma
Hadruridae
Hairy tail
Large
Front of prosoma curved outwards
Superstitioniidae
Vaejovidae
Front edge of prosoma mostly straight with only slight notching
One of the most diverse family of scorpions, highly variable in appearance
References
Francke, O. F. 1975 . A new species of Diplocentrus from New Mexico and Arizona (Scorpionida ,
Diplocentridae) . J. Arachnol. 2 :107-118 .
Haradon, R. M. 1983 . Smeringurus, a new subgenus of Paruroctonus Werner (Scropiones, Vaejovidae).
J. Arachnol., 11 :251-270.
Soleglad, Michael & Fet, Victor. (2004). The systematics of the scorpion subfamily Uroctoninae (Scorpiones: Chactidae).. Revista Ibérica de Aracnología. 10.
Stockmann, R., & Ythier, E. (2010). Scorpions of the World. N.A.P. Editions.
Stahnke, H. L . 1974 . Revision and keys to the higher categories of Vejovidae (Scorpionida). J .
Arachnol. 1 :107-141 .
Stockwell, S. A. and J. A. Nilsson. 1987. A new species of Diplocentrus Peters from Texas
(Scorpiones, Diplocentridae). J. Arachnol., 15:151-156.
Williams, S. C. (1980). Scorpions of Baja California, Mexico, and Adjacent Islands. OCCASIONAL PAPERS OF THE CALIFORNIA ACADEMY OF SCIENCES.
Photos used were primarily taken off of inaturalist, though some of them are my own.
Here's the Google Doc where everything's together as well.
And what I really wanted to show you guys, a side by side comparison of the two species! The h. petersii is a mature female, here being compared against a mature male h. spinifer (except the ventral shot, that one is of the mature female h. spinifer). You can right away see the dramatic size difference and what people mean when they say "matte black" vs "shiny black". H. spinfers also have red telsons, and are much more heavily granulated.
