16ª JORNADAS DEL GRUPO IBÉRICO DE ARACNOLOGÍA

     
 

Venom metering in scorpions under controlled threat levels

 
 

 

 
 

Mykola Rasko1, Arie van der Meijden2, Pedro Coelho2

 
     
 

1Universidade de Coimbra - Pólo II; 3030-790 Coimbra, Portugal.

 
 

 

 
 

2CIBIO Research Centre in Biodiversity and Genetic Resources, InBIO, Universidade do Porto, Campus Agrário de Vairão, 4485-661 Vairão, Vila do Conde, Portugal.

 
 

 

 
 

Scorpion venom is a complex mixture of toxins. A lot of work is being done on the biochemical properties of the scorpions venom and not that much of work has yet been performed on the biomechanical aspects of scorpion venom delivery. The amount of venom released during different stings is known to be different. Scorpions, just like snakes and spiders, have the ability to meter the amount of venom they want to expel. Production is an expensive metabolic investment. In scorpions metabolic rate gets up to 39%, for milked specimens compared to the unmilked ones. Factors like the amount of total venom present in the scorpion's venom glands at that moment and the perceived level of threat to the scorpion, can influence the released venom volumes. In this study the level of threat was manipulated in order to test its influence on the volume of released venom. Hadrurus arizonensis, was the species chosen for the experiment. Two hypothesis where formed. The first one defends that scorpions are able to meter the amount of venom they expel. The second one states that larger quantities of venom are expected to be released by the scorpions, as the level of threat increases. Our results show that during ten consecutive attacks to which scorpions were exposed in rapid succesion, venom volume released on each attack is being controlled by the scorpion, changing the amount of released venom between the attacks. Overall, the amount of venom released on consecutive attacks decreases, but there is high inter-individual variability. The number of dry stings, where no venom is released whatsoever, increases with the number of consecutive threats, and also varies by individual. By the end, we did accept the first hypothesis, and reject the second one.

 
     
 

Keywords: Hadrurus arizonensis; consecutive attacks; dry stings