This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Some animals defend themselves by spraying liquid at potential threats. Perhaps the most well-known example of this is the skunk, whose spray contains chemicals that smell awful to the animals it’s defending itself from. Other animals have slightly more exciting chemical sprays. Bombardier beetles can actually spray a chemical that is 100 ?C (212 ?F) as shown in David Attenborough’s ‘Earth’ series (a clip of which can be found here). They do this through a series of chemical reactions inside their body that then release the boiling liquid at exactly the right time (to prevent it burning itself).
While less glamorous than a boiling chemical spray, a lot of animals are pretty good at spraying their urine and faeces in defence. I didn’t know this before I started working with bumblebees, but they can spray their faeces. I’m not sure if it’s intended as a defence mechanism or not, but when trying to tag them with numbers (to keep track of which bee is which) I’ve gotten pretty good at learning to dodge when a yellow liquid goes flying towards me.
Other animals spray toxic venom to defend themselves. Spitting cobras can accurately aim a stream of venom towards an aggressor. This reminds me of another great Attenborough clip:
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At least seven species of scorpion also spray venom to defend themselves. However, making a chemical like venom can be costly, and a scorpion wouldn’t want to waste it by spraying every potential predator. I’ve previously written about black widow spiders, who are faced with a similar problem when deciding whether and how much venom to eject into their bites
A recent study by Zia Nisani and William K. Hayes at Loma Linda University in California found that at least one scorpion (the South African Spitting scorpion) controls whether it sprays venom depending on the level of threat. When the researchers grabbed the scorpion by its tail with forceps the scorpion would sometimes spray venom at them. However, the scorpion was much more likely to spray venom if this was accompanied with a puff of air. Why might this be? Well, scorpions have sensory hairs on their legs that help them detect both predators and prey. Therefore, having two cues of a predator at once (both being grabbed by the tail and a sudden puff of air) seems to cause a bigger reaction from the scorpion than just a single cue. This might be comparable to if you heard a loud bang and saw a sudden flash of light you might be more likely to yell than if you just had one of these things happen.
The researchers also found that when the scorpion started to spray, it would make rapid movements which meant that the stream of its spray would be spread around a wider area and therefore be more likely to hit a potential predator’s eyes. This is similar to what spitting cobras do when they spray venom: they move their heads around in an undulating motion.
This study shows that scorpions can control when and how they spray their venom at predators, saving it for when its really necessary and doing their best job to hit a predator where it hurts.
A video of one of the scorpions used in the experiment spraying its venom:
Photo Credits
Sprayed dog: Mike Mozart
Parabuthus transvaalicus: Bgqhrsnog
Video credit
Credit: Dr. William K. Hayes Lab (Department of Earth and Biological Sciences, Loma Linda University)
Reference
Nisani, Z., & Hayes, W. K. (2015). Venom-spraying behavior of the scorpion Parabuthus transvaalicus (Arachnida: Buthidae). Behavioural processes, 115, 46-52.
