Why do some scorpions climb onto scrubs in Spain?

Foraging behavior in scorpions (as in all animals) is balance between food availability and predation risk. And in scorpions, cannibalism is a well known risk, especially when individuals of different sizes live in the same population. Distribution and behavior of foraging scorpions will therefore be shaped by resource availability and predation risk.

Francisco Sánchez-Piñero and Fernando Urbano-Tenorio have recently published a study on foraging behavior and shrub climbing in the buthid Buthus occitanus (Amoreux, 1789) in Spain. The study did not support a hypotheses explaining shrub climbing based on resource availability, but did support to the hypothesis that shrub climbing in the scorpion Buthus occitanus is related to predator (cannibal) avoidance.

Abstract:
The distribution and behavior of foraging animals usually imply a balance between resource availability and predation risk. In some predators such as scorpions, cannibalism constitutes an important mortality factor determining their ecology and behavior. Climbing on vegetation by scorpions has been related both to prey availability and to predation (cannibalism) risk. We tested different hypotheses proposed to explain climbing on vegetation by scorpions. We analyzed shrub climbing in Buthus cf. occitanus with regard to the following: a) better suitability of prey size for scorpions foraging on shrubs than on the ground, b) selection of shrub species with higher prey load, c) seasonal variations in prey availability on shrubs, and d) whether or not cannibalism risk on the ground increases the frequency of shrub climbing. Prey availability on shrubs was compared by estimating prey abundance in sticky traps placed in shrubs. A prey sample from shrubs was measured to compare prey size. Scorpions were sampled in six plots (50 m x 10 m) to estimate the proportion of individuals climbing on shrubs. Size difference and distance between individuals and their closest scorpion neighbor were measured to assess cannibalism risk. The results showed that mean prey size was two-fold larger on the ground. Selection of particular shrub species was not related to prey availability. Seasonal variations in the number of scorpions on shrubs were related to the number of active scorpions, but not with fluctuations in prey availability. Size differences between a scorpion and its nearest neighbor were positively related with a higher probability for a scorpion to climb onto a shrub when at a disadvantage, but distance was not significantly related. These results do not support hypotheses explaining shrub climbing based on resource availability. By contrast, our results provide evidence that shrub climbing is related to cannibalism risk.

Reference:
Sanchez-Pinero F, Urbano-Tenorio F. Watch Out for Your Neighbor: Climbing onto Shrubs Is Related to Risk of Cannibalism in the Scorpion Buthus cf. occitanus. PLoS One. 2016;11(9):e0161747. [Open Access]

Thanks to Matt Simon for informing me about this paper!