Scorpions adapt their stings, stings and sting contents to minimize the costs of using venom

Replenishing venom takes time and energy – so it pays to be stingy with bites.

According to researchers at the Australian National Institute of Tropical Health and Medicine, scorpions adapt their bodies, their behavior and even the composition of their venom, to effectively control their prey and predators.

Write in Borders in ecology and evolutionThey say that what matters is not only the size of the stinger, but also the way it is used.

Stingers stingy

"Scorpions can only store a limited volume of venom, which takes time and energy to replenish after use," said lead author Edward Evans. "In the meantime, the scorpion has a reduced ability to capture prey or defend against predators, so the cost of using venom is twofold."

As a result, more than 400 million years of scorpion evolution have developed various strategies to minimize the use of venom.

The most obvious is to avoid using venom.

"Research has shown that lighter, faster male specimens belonging to one species are more likely to flee the danger than heavier females than to expend energy using toxins," notes Evans. "Others, especially the burrowing species, are more likely to depend on their large claws or" pedipalps "and possess a scathing little device, rarely used."

When immobility, a threat or a hard prey compels the use of venom, scorpions can adjust the volume injected – both inside each sting and by the application of multiple stings.

"The scorpions can hold their prey in their pedipalps and wisely apply their stings, until they stop struggling."

At the other extreme, when the stakes of survival are high, some species give up accuracy and spread their venom in the air.

"Spraying venom defensively is potentially a waste of time, but can avoid dangerous close contact with predators such as grasshopper mice, which disarm scorpions by biting their tails."

Versatility Venom

Scorpions can also adapt the composition of their venom to a target, both on the fly and more specifically during weeks of exposure.

For starters, any given sting has three levels: dry, prevenom or venom.

As a mild deterrent, a scorpion can sting without any venom. A "wet" sting starts with a clear, salty predominance – essentially a stun parameter – and may not go further.

"Research on prevenom suggests that it contains an extremely high concentration of potassium salt, which can cause rapid paralysis in insects and vertebrate pain," Evans said. "It seems to regenerate quickly and presumably at a low metabolic cost."

If things get heavy, the scorpion can continue to inject or spray a thick, milky, protein-rich venom.

"The venom injection is reserved for more active, persistent or important targets.It is more toxic, but once consumed, it takes weeks to replenish it, leaving the scorpion vulnerable and has a limited number of prey. "

Recent work by the James Cook University group suggests that scorpions may make more personalized modifications to venom composition, in response to long periods of exposure to predators.

"Repeated encounters with a surrogate vertebrate predator – a taxidermal mice – over a six-week period led the scorpion Hormurus waigiensis to produce a higher relative abundance of a particular group of toxins, including some with activity. vertebrate predator specific, "says Dr. Dr. David Wilson.

How exactly the change occurs remains unknown, however.

"Future work is needed to determine to what extent the observed changes in venom composition and use are due to adaptive responses – and to identify the precise stimulus of change," conclude Wilson and Evans.