Tag Archives: Texas horned lizard

Not in Front of the Girls, Phrynosoma cornutum!

Phrynosoma cornutum

Phrynosoma cornutum, or the Texas horned lizard, has armed itself with an impressive array of defenses, but none quite as gruesome as its tendency to squirt jets of poisoned blood from its eye sockets to deter attack. Otherwise known as ‘autohaemorrhaging’ horned lizards are the only known vertebrates to use this defense mechanism.

A highly cryptic, or well-camouflaged, species from the dry areas of Southern U.S. and Mexico, P. cornutum relies on its colouration, flattened body form, and lateral fringe scales to keep it hidden from predators. However, when it is detected by predators, it can defend itself with its toxic blood-jets, or flee. The defense mechanisms and behaviour of P. cornutum have been studied by William Cooper of Indiana University-Purdue University and Wade Sherbrooke of the American Museum of Natural History to determine if a notion known as ‘escape theory’ applies to highly cryptic species such as P. cornutum as it does with more conspicuous species. “Of  particular interest is whether their escape decisions bear the same relationship to predation risk and costs of escaping as they do in other prey lacking such defenses,” said Cooper and Sherbrooke.

Escape theory predicts that once an animal has detected a predator nearby, it will not flee immediately, but instead monitor the predator’s approach and base its decisions on the apparent costs and benefits of the situation. It will assess the risk of getting caught versus the cost of fleeing from its current location – which could mean lost opportunities to forage for food or engage in social behaviour. When it does decide to flee, its level of fitness will determine the initial distance between it and its predator, a space known as ‘flight initiation distance’. The fitter the prey, the shorter the distance left between them.

What the reseachers found when observing P. cornutum was that the individuals who were alone when spotted by a predator had an average flight initiation distance almost twice as long as those who were in the company of other lizards and interacting socially with them. Thus the predictions of escape theory held true. “The decrease in flight initiation distance during social encounters provides the first evidence that horned lizards base their escape decisions in part on costs associated with fleeing,” Cooper and Sherbrooke said.

Texas horned lizard blood

Another small animal with a rather terrifying defense mechanism is the Trichobatrachus robustus, or Hairy Frog, so called because when the males breed, they produce strands of skin and arteries that look like long hairs. When threatened, much like the Spanish Ribbed Newt that pushes its ribs through its skin to use as weapons, these frogs break their own bones and push them through the skin on their toe pads to form claws.

Observed in detail by David Blackburn and colleagues at Harvard University, T. robustus’ claws are an instant weapon, and dangerous enough to force the people of Cameroon to hunt them with long spears and machetes to avoid some nasty wounds.

Trichobatrachus robustus claws

When at rest, these claws are hidden inside the tips of the hind feet, surrounded by a mass of connective tissue. A small piece of bone at the tip of T. robustus’ toe is connected by collagen to the sharp end of the claw. The back end of the claw is connected to a muscle, which Blackburn suggets can be contracted when the animal is threatened, pulling the claw downwards, and breaking the collagen bond between sharp tip of the claw and the bony end of the toe. The claw emerges through the skin on the underside of the frog’s hind toes, far enough to leave “deep, bleeding wounds to the person holding it,” according to the paper pubished in Biology Letters.

Also found in other African frogs from the Astylosternus genus, Blackburn reports, “No other vertebrate claw is known that lacks a keratinous sheath, is composed soley of naked bone, and must break free from another skeletal structure to pierce its way to functionality.”

Cameroon Hairy Frog claw

Hey, P. cornutum, T. robustus – promise me you’ll never get into a fight, especially in front of girls?

You know what it would be like. You’ll be walking between classes together or something one day, like, “And then my mum walked in and I got cereal and milk all over the sheets,” “That’s gross,” when you’ll accidentally bump into a Greater Roadrunner who’s mad about his crap grades and he’ll be all, “HEY! WATCH WHERE YOU’RE GOING, NO EYES.”

And you’ll be like, “Why are you yelling?”


“Yeah? Well we can’t see yo–“


“I’m a b–“


“Shit. We’re going to die. We’re going to die in front of girls.”

“What are you talking about? We have the most awesome weapons ever. You can make bone claws, and what’s he gonna do? Peck?”

“Hey you’re right. We should invite girls.”

“Yeah. Lots of girls. Because this will probably be the best moment of our lives.”

So you’ll do your mythology quiz, “If in doubt, just write ‘castrated’…” and then head over to the demountables. Of course, the Roadrunner will be late, so you’ll be like, “I wonder what I’d look like if I had feathers.”

“A chicken.”


Then the Roadrunner will arrive, and so will all those girls you invited. You’ll shoot mad blood tears at the Roadrunner, and probably accidentally at the girls too, judging from the way they’ll carry on like, “Oh my god, we’re covered in blood.”


“Birds can’t get hepatitis.”


And somewhere between their mutterings of “That was the grossest thing I’ve ever seen,” and “If I ever accidentally make out with either one of them at a party because I’m really really super drunk, promise me you’ll kill me and immediately stop being my friend?” the girls will have decided to never ever date you.

“Shooting blood out of your eyes? What is that? What’s your next move? Opening your chest cavity and using your guts to tie that Roadrunner to a bicycle before wheeling him to the top of a hill and pushing him down so he’ll get runover and crushed and all tangled up in your guts?”


“Well are you going to take your own eyeballs out and dip them in poison and then force him eat your poison eyeballs and then laugh when he dies because of your poison eyeballs?”

“Um. No…”

“Are you gonna tear off your own head and put it in a sandwich and–“

“OR… how about I push my own bones through my skin to make claws? Bone claws! That’s cool, right? Girls?”


For more info visit New Scientist’s Zoologger page.

Original paper on P. cornutum from Ethology here /On T. robustus from Biology Letters here.
Top image by Jack Goldfarb / T. robustus images courtesy of D. Blackburn.

– bec



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