Water pistol defence! Squirting snakes, mammals and bugs.
First off, before I start the blog I would like to talk briefly about my last post.
I talked about how academics will say poisonous snakes, which when they mean venomous. I was talking to a senior lecturer in my department recently (who’s German) and we discussing the subject, and he said that in many languages there is no two words for venom and poison (I think in German it’s “gift”). Knowing this, I just want to say that I apologise to those scientists who do not have two words for venom and poison, as it is a fairly recent etymological event in English and may not have spread to other languages.
Anyway, onto the new blog!!
My cousin recently found out about the spitting cobra (this isn’t one species, there are many of both Asian and African species of Naja that “spit” venom, and that of the monophyletic genus Hemachatus) and was telling me about it. Me, being a wonderful older cousin listened with interest and was enthusiastic, and then it occurred to me how amazing a projectile system is as a defence.
Think about it, it makes perfect sense. You keep your distance and deter the threat without putting yourself in danger. Even humans do it; we developed spears and sling shots to throw, and then bow and arrows to shoot, and then eventually guns. So many animal “attacks” are dealt with with firearms, a woman gets too close to a polar bear in the zoo and it grabs her and the police shoot the bear, they don’t go in and go 12 rounds with the massive creature they keep are far away as they can.
Spitting cobras are probably the most well-known group of animals that shoot something yucky in defence; the adapted fangs enable them to accurately project venom quite a distance. Other animals aren’t as gifted as these wonderful elapids. Some viper species have been noted to flick venom (the only one I could find is http://en.wikipedia.org/wiki/Trimeresurus_mangshanensis), which although is an amazing way of defence, is nowhere near as effective as spitting cobras.
Skunks are fairly well know sprayers, they will spray a grim smelling cocktail of chemicals from anal glands at threats, and the smell lingers for quite a while. This behaviour is also seen in invertebrates. The bombardier beetles will spray chemicals from the end of their abdomen. The biology behind the spraying mechanism creates a lot of heat raising the liquid to nearly 100oC. This hot, enzyme filled mixture is under pressure when expelled resulting in a very quick behaviour, often lasting less than a second. Grasshopper species Poekilocerus pictus and Parasanaa donovani (both Indian and SE Asian species) squirt liquids from their thoraxes when attacked.
I think the best water pistol defence mechanism is by far the Horned Lizard (of the Genus Phrynosoma), also known as Horned Toads. When threatened they will stay still, hide, puff up to avoid being attacked, but as a last resort (as many of these mechanisms are as they are energically and physiologically expensive to use) the lil reptile does something amazing. It will squirt blood from its eyes. The way they do this is by increasing pressure in the head by restricting blood flow away from the head and rupturing blood vessels around its eyes. This causes the blood to squirt out at sometimes quite a distance. This would freak me out if it happened to me, so I don’t know how I would react if my had dinner had just done that!!
I find it hard to believe that I can only find a few examples of this wonderful way of predation deterrence, there may be many more I can’t find.
http://www.youtube.com/watch?v=GgB4u6Mgy2M – horned lizard video