Beware the pregnant scorpion

Male striped bark scorpions (Centruroides vittatus) are faster than the females, who are more likely to sting.

Matthew Rowe

It’s hard to feel sorry for a scorpion, but if you were pregnant for 80 percent of the year, you might be a bit cranky, too.

Female striped bark scorpions spend the majority of their lives hefty with young, and that has made them slower than their male counterparts and more likely to sting, Bradley Carlson of Pennsylvania State University and colleagues report May 28 in PLOS ONE.

Striped bark scorpions are medium-sized arthropods commonly found in the southern United States and northern Mexico, where they eat small invertebrates and, in turn, get eaten by birds, snakes and other critters.

Carlson and colleagues collected dozens of scorpions in the Organ Mountains of New Mexico and brought them back to the lab. There, they housed their finds in plastic sweater boxes outfitted with gravel floors, cardboard egg crates for shelter and petri dishes filled with water — what more could a transplanted scorpion want?

Female striped bark scorpions (bottom) have longer tails. Males’ legs (upper right) are built for sprinting. Carlson et al.

The researchers measured how fast the scorpions could sprint and how fast they would sting. They also measured the animals’ temperament — by grasping each one by the base of the tail with metal forceps, holding it above its container home for 15 seconds and watching if the scorpion tried to sting the forceps. Then the researchers stuck each scorpion in a freezer (apparently the best way to kill them for science) and later weighed and measured its parts.

Females had heavier bodies and shorter legs, and they weren’t able to sprint as fast as the guys. “The males, unburdened by parenthood, are effective sprinters that have evolved longer legs to support predator evasion and mate-seeking,” Carlson and colleagues write.

If the females can’t run away from a potential predator, they can still defend themselves: Female scorpions stung at a rate higher than the males. And in the temperament test, 75 percent of the females attempted to sting the forceps in at least one trial; no males did that.

Stinging actually isn’t the best option for dealing with a predator because producing venom has a metabolic cost, and replacing that venom takes time. “It is perhaps unsurprising that scorpions would sometimes avoid stinging if other options (e.g. fleeing) are available,” the researchers write.

But for a female scorpion trying to gestate her young, well, being big and slow limits those options. Stinging is her best bet.  

Sarah Zielinski

Sarah Zielinski is managing editor of Science News for Students. She has a B.A. in biology from Cornell University and an M.A. in journalism from New York University. She writes about ecology, plants and animals.

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