Variability in venom volume, flow rate and duration in defensive stings of five scorpion species

The venom optimization hypothesis says that scorpions (and other taxa using venom in defense and in prey capture) should use the venom carefully because the venom used can sometimes represent a large, costly, metabolic investment, and can take a long time to replenish. Several studies support this hypothesis for scorpions.

Arie van der Meijden and co-workers have now published a study investigating the variability in venom volume, flow rate and duration in defensive stings of five scorpion species. Both venom flow rate and flow duration correlate highly with the total expelled volume, indicating that scorpions may control both variables in order to achieve a desired end volume of venom during a sting.

Abstract:
Scorpions have been shown to control their venom usage in defensive encounters, depending on the perceived threat. Potentially, the venom amount that is injected could be controlled by reducing the flow speed, the flow duration, or both.We here investigated these variables by allowing scorpions to sting into an oil-filled chamber, and recording the accreting venom droplets with high-speed video. The size of the spherical droplets on the video can then be used to calculate their volume. We recorded defensive stings of 20 specimens representing 5 species. Significant differences in the flow rate and total expelled volume were found between species. These differences are likely due to differences in overall size between the species. Large variation in both venom flow speed and duration are described between stinging events of single individuals. Both venom flow rate and flow duration correlate highly with the total expelled volume, indicating that scorpions may control both variables in order to achieve a desired end volume of venom during a sting.

Reference:
van der Meijden A, Coelho P, Rasko M. Variability in venom volume, flow rate and duration in defensive stings of five scorpion species. Toxicon. 2015 Apr 24;100:60-6. [Subscription required for full text]

Thanks to Arie van der Meijden for sending me his article!