26 November, 2018

The defense respons of scorpions to repeated attacks from a predator

Scorpions and other prey species are involved in a continuing arm race against their predators. The prey will get better in avoidance and defence and the predator tries to get better in overcoming the prey.

Mykola Rasko and co-workers have recently published a study investigating the sting use and venom expenditure during repeated attacks (simulated) in Hadurus arizonensis Ewin, 1928 (Caraboctonidae). Contrary to the projects expectations, the stinging behaviour, venom use and venom volume all decreased as the number of challenges increased. The scorpions defenses actually decreased during repeated attacks. This means that a predator of scorpions should use repeated attacks to overcome a scorpion, and this is also something that has been observed in some predators of scorpions.

Predatore-prey arms races ensure that a prey's defences are well matched with the predator's ability to overcome them. Scorpions have a formidable defensive capacity due to their venomous stinger. Mammalian and squamate scorpion predators overpower scorpions by making repeated attacks. We tested here how scorpions, Hadrurus arizonensis, apply their venom defensively during a simulated repeated attack, consisting of 10 consecutive challenges. Since the persistent repeated attack of a predator, even when stung in the process, seems to indicate its resolve, we expected defensive effort to increase with the number of challenges. We also expected that, owing to the life-and-death nature of a predatory attack, scorpions would be liberal in the use of their venom. We found, however, that stinging behaviour, venom use and venom volume all decreased as the number of challenges increased. Scorpions used only 7.8±9.6% (mean±SD) of their total venom volume during an attack consisting of 10 consecutive challenges. We conclude that a repeated attack seems an effective strategy for scorpion predators to reduce the defensive investment of scorpions.

Rasko M, Coelho P, Simone Y, van der Meijden A. How to attack a scorpion: venom metering during a repeated attack. Anim Behav. 2018;145:125-9. [Subscription required for full text]

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