This is it, your back is against the wall, it’s life or death.
What do you do?
Do you pull off your arm and run for it? Do you smear yourself in faeces? Or just drop and play dead?
Nature, in its infinite wisdom, has created some truly fascinating and disgusting ways for inhabitatants of the animal kingdom to defend themselves. Of course there are a multitude of interesting physiological and behavioural defences out there, but today I’m focusing on a handful of the more unsavory tactics employed by animals that must either be fiendishly innovative or down-right desperate.
Making A Mess
This section heavily features blood, poo, vomit and the animals that use these to their advantage. Just as many of the creatures in this article would say (albeit with gross bodily fluids and not words), you’ve been warned.
As a truly bizarre example of predator deterrence, the Texas horned lizard (Phrynosoma cornutum) and a few close relatives have the ability to build up the blood pressure around the eye to such an extent that it can squeeze blood from their eyes at high velocity towards targets up to 1.5 metres away. A sudden squirt of blood in the face not only confuses the lizard’s attackers but the blood of these lizards contains a chemical that is foul-tasting to canine predators such as wolves and coyotes.
Similarly, wood snakes of the genus Tropidophis are known to fire blood from their mouth, nostrils and eyes when threatened and the European grass snake (Natrix natrix) can secrete blood from its mouth and nose whilst feigning death to escape predation.
However, this blood-cannon quirk is far from unique to the reptiles and invertebrates such as armoured ground crickets (Acanthoplus discoidalis) and katydids that can also squirt their haemolymph to ward off potential attackers.
If you thought blood was gross, you might want to hold your nose for these next few animals. It’s not controversial to treat poo as something to be avoided, unless you’re a dung beetle. Or a termite. Or a rabbit. Or a dog. Or an elephant. OK, a wide variety of animals have a certain investment in poo, but when used as a weapon, it can have deadly results.
The larvae of the three-lined potato beetle (Lema trilinea) can be an attractive treat for a variety of predators, but they have developed a self-sustaining shield to ward off enemies. The preferred meal for these larvae is nightshade and other plants containing alkaloids that are toxic to animal predators, meaning that their faeces is also to be avoided if you’re a predator that enjoys a pain-free life. The larvae exploit this fact by directing their excretions on to their own back, building up an impressive fecal (or ‘frass’ for you insect boffins) shield.
A similar tactic to the ink-jets observed in cephlapods such as squid and cuttlefish has also been employed by pygmy sperm whales (Kogia breviceps), who can release up to 12 litres of viscous dark brown liquid from an intestinal sac when threatened. This “squid tactic” acts as both a means of confusing and diverting the predators as well as actively repelling them. Here’s a taste of what to expect:
It’s not just animal anuses (never thought I’d have to check the plural of anus) that have all the fun, let’s get the mouths in on the action! As previously mentioned, many animals can autohaemorrhage from their mouths, but for those species not willing to give up their blood, there is another option. Eurasian roller birds () and Northern fulmars () are both known to resort to vomiting foul-smelling liquids to ward off predators and Turkey vultures () have been observed rapidly emptying the undigested contents of their crop to lighten their bodies and enable a speedier aerial escape.
No Pain, No Gain
These next two animals have one truly extraordinary thing in common: they can both shove their bones through their skin as defensive weapons.
The hairy frog (Trichobatrachus robustus), also known as the Wolverine frog, is a species of frog native to central Africa that has earned its nickname due to its ability to project retractable bone ‘claws’ through the skin of the toes when grabbed or attacked by a predator. These claws are nestled inside the toes and connected to a small bony nodule by strands of collagen, which can be severed by contracting muscles around the nodule and forcing the claw outwards through the skin to stab the perceived threat.
The Iberian ribbed newt (Pleurodeles waltl) has a similar trick under its slimy sleeves. Instead of having bone-claws appear from the tips of the toes, these newts are able to swing their ribs forwards so that the tips protrude through the skin as a wall of spines. This is not the newt’s only method of defence. It is also able to secrete a poisonous substance onto its skin, which can turn these pointy ribs into needles capable of injecting the deadly poison into the skin of its attacker. The act of pushing the ribs through the skin appears to have no lasting damage to the newts and proven to be an effective method of keeping predators at bay.
You Want A Piece Of Me?!
Autotomy, the act of self-amputation, is prehaps most commonly associated with lizards and other small reptiles. When cornered by predators, many species of lizard, gecko and skink are able to detach both their tail as a distraction to predators. But don’t call the vet just yet! The lizards are able to contract sphincter muscles surrounding the injury site in order to minimise blood loss. They also have impressive tissue regeneration, so sacrificing a tail in the short-term to escape a predator is undeniably better than holding on to it and becoming a more nutritious snack. Interestingly, once a lizard tail is autotomised, it performs a rythmic series of contractions that are intended to distract the predators towards the movement of the tail and enable the rest of the lizard to escape.
There are handful of mammals that are also capable of detaching parts of their body in order to evade predation. At least two species of African spiny mice (Acomys kempi and Acomys percivali) are able to release themselves from patches of skin that are in the grasp of a predator. These mice also show remarkable tissue regeneration for mammals. Skin, hair follicles, sweat glands, fur and cartilage can all be regrown with little or no evidence of scarring, leading researchers to believe that they might be useful in identifying genes involved in tissue regeneration in humans. The edible dormouse (Glis glis) is also capable of limited autotomy, as their tails can easily be detached if grabbed by a predator. However, unlike the reptiles, once the tail is gone, it’s gone for good.
Sea cucumbers can go one further. Some species are able to eviscerate themselves, or eject their internal organs as a defence strategy. When threatened, species such as Holothuria leucospilota and Holothuria foskali are able to fire a couple of hundred Cuvierian tubules (which make up the respiratory tree) from their body out into the water. These tubules contain a toxin called holothurin, which is deadly to many aquatic animals. When they are ejected, they also undergo a rapid extension and can reach many times their original length within the body, as well as becoming very strong and adhesive which enables them to immbolise potential predators. Whilst these tubules encase the predator, the sea cucumber can disengage and escape to safety, where it can regenerate its tubules over a number of weeks. This process is shown below, in all its gory glory.
The pelagic squid with a fantastic latin name, Octopothethis deletron, has a rather similar trick. As well as being able to shoot a cloud of ink, it is also able to attach one of its arms onto its pursuer and rapidly jet away, leaving the arm attached to the predator as a farewell gift.
There are a variety of species that have adapted unique defensive weapons in the eternal arms race between predator and prey. Hagfish (eel-like fish of the class Myxini) are one of the Earth’s greatest survivors, having existed relatively unchanged for about 300 million years. They’re clearly doing something right, and it might have something do to with their biological super-weapon. SLIME.
Hagfish have glands along their flanks that produce a substance that generates a sticky and gelatinous fluid when combined with water. When a predator attempts to grab a hagfish in its jaws, it will quickly realise that instead of finding flesh, it will find a mouthful of viscous gel that will quickly clog the gills. Hagfish slime is currently being researched quite intensely as the properties of the slime may open up new applications in bio-inspired synthetic materials.
Bombardier beetles (over 500 known species within the family Carabidae) also produce a substance that can strike fear into the hearts of any potential predator. When threatened, the beetles can decompose stores of hydrogen peroxide and oxidise hydroquinone within a vestibule that is lined with catalases. This quickly begins a chain reaction that ends with an incredibly exothermic reaction, capable of generating energy as heat that raises the temperature of the mixture to almost 100ºC! The pressure built up during these reactions expels the boiling liquid from the body as a foul-smelling and irritating gas towards the direction of the threat.
Whilst not as painful as a searing-hot blast of painful chemicals, the anal scent spray of skunks (carnivores in the family Mephitidae) is notorious for its stench. These glands produce offensive scents made from chemicals that contain sulphur and are incredibly odorous to a wide range of potential predators. For this reason, many predators that would hunt mammals of the skunk’s size tend to avoid them as prey to avoid getting a faceful of this stinky spray.
You may have seen photos or videos of the ridiculously adorable slow loris (primates of the genus Nycticebus) on the internet, but beware, there’s more to them than meets the huge-round-lovable-eye. In their armpits hides a gland that secretes a toxin. When the slow loris licks this gland, the saliva reacts with the toxin and creates a toxic bite intended for any unwary attacker.
I hope this article has enlightened and disgusted you! Thanks for reading!