Determining the sex of adult (and in most cases subadult) scorpions is not exceptionally difficult. Unfortunately, there is not one single characteristic that will work for all scorpions. One must learn which characters work best for the species at hand. Following are some characters that are known to exhibit sexual dimorphism.
Pectinal Tooth Counts. Generally, males have higher pectinal tooth counts than females. However, in many cases, the male and female counts in a given population or species will overlap significantly, so caution must be exercised. Check the ranges in pectinal tooth counts provided with species descriptions. In the genus Paruroctonus (Vaejovidae) males and females have altogether non-overlapping counts, making this the best method to sex specimens for that group.
Pectinal Structure. Even when counts of pectinal teeth overlap significantly, it is often possible to determine the sex of the scorpion by the size of the pectines themselves. In many buthids the male pectines protrude distally beyond the coxa-trochanter joint of the 4th leg. In the female, the tip of the pectines do not reach this joint. The pectinal teeth in males of non-buthids especially are larger and distinctly angular (banana-shaped); those of females are smaller and evenly elongate-oval, or even peg-like. Another general characteristic that serves well to distinguish males and females of many scorpions (but usually not buthids) is the angle formed by the posterior margin of the tooth row and the medial margin of the pectinal shaft. In males these margins form a right angle (or nearly so), whereas in females it forms a distinctly obtuse angle.
Genital Papillae. Males of most scorpion taxa have small fingerlike projections called genital papillae protruding beneath the posterior medial edge of the genital opercula.
Shape and Structure of the Pedipalp Chela. The shape of the pedipalp chela varies sexually in many taxa. In many vaejovids, the male chela is more robust, has shorter fingers, and bears stronger keels (ridges). In some scorpions, the male chela may be carinate and the female chela entirely smooth. Another interesting feature of the chela is the presence of “scalloping” along the cutting margins of the chela fingers. By definition, the fixed finger has a rounded recessed area and the movable finger a lobe that fits into it. This character is more pronounced in male scorpions, and in some is very pronounced.