Pedro Coelho, Antigoni Kaliontzopoulou, Mykola Rasko and Arie van der Meijden
There are almost 2,500 species of scorpions in the world, and many differ in the shape and size of their venomous tail*. The reasons for this large variation in tail shape are often not known. While scorpions sting their insect prey slowly and precisely, they defend themselves from attackers with a fast and swooping strike of their tail. The defensive strike may therefore be the more demanding behavior that a scorpion performs with its tail. In this study we measured the strike speed of scorpions for the first time. We also investigated if there are differences in the arc that the stinger, which sits at the end of the tail, describes during such a defensive strike.
We recorded the tail strikes of scorpions using high-speed video, and reconstructed the stinger’s trajectory in 3D. Comparing the 3D shapes of the strikes of seven different species, we found that there are differences between the species. However, some very similar species did not differ in the shape of their tail strike. We also compared the well-known and dangerous “fat-tailed scorpion” to a close relative with a much less thick tail. These two species did show differences in the shape of their tail strike and also differed in the maximum speed of the strike, with the fat-tailed scorpion being the faster one.
Some tail strikes were “closed”, almost returning to the start position, while others were more “open”, with the start point and the end point further from each other. More “open” shapes were faster that more “closed” shapes.
Our results show that species, body size, and tail thickness and length, may be important factors in determining the shape, speed and acceleration of the defensive tail strikes of scorpions.
*It should be noted that the “tail” of a scorpion is really a continuation of its body, with only the stinger at the end being the true tail.