There’s some bad blood between us!


Ever felt afraid by your normal household lizard?

Then what about a lizard fully covered with horns that can spurt blood through its eyes? Ack.

Horned lizards, also known as Phrynosoma cornutum ,  despite the spikes and blood that can spurt up to 1 metre (for their averaged 13cm long body) (Berger & Berger 2009) , they are still preyed upon.

Biology of the phenomena

Closure of the jugular internal veins and swelling of the venous sinuses loosen the tight skin covering the head during ecydysis (Bruner, 1907). Blood passes into the lower eyelid (conjunctival sac) and is propelled from the venous sinuses of the lid after it has been distended by closure of the internal jugular constrictor muscles (Burleson, 1942).

This mechanism, commonly known as autohaemorrhaging is commonly found in insects, horned lizards seem to be the only group of vertebrates that do it. (Bateman & Fleming 2009)

Purpose of the phenomena

There is a fluid from the Lacrimal or Harderian glands which is added to the blood before ejection ( Burleson 1942, Heath 1966, Cowles 1977, Middendorf et al., 2001). Dogs are particularly vulnerable to the blood, once they get sprayed they will shake their heads to get rid of it. (Sherbrooke & Middendorf 2004).

The blood also contains a factor enabling it to detoxify the venom of its preys such as ants  (Schmidt et al 1989).

 Occurence of the phenomena

Hoping to see this behavior? Strangely,this response is not always elicited. Dog  attacks elicited blood squirting (70-100% of encounters) (Middendorf & Sherbrooke 1992) whereas, attacks by another known predator, Greater Roadrunners did not (Sherbrooke, 1990). Also, a canid was more likely to elicit blood-squirting (100%) than a canid-mimicking human (20%). (Sherbrooke and Middendorf 1992). As if there might be learning of its predator.

Although this is a distinctive trait out of the horned lizards, smaller species of the horned lizard (Phrynosoma modestum and Phrynosoma douglasii ) do not have this defence (Sherbrooke and Middendorf 2001).


Hmm, so the horned lizard doesn’t so scary anymore huh? As the little lizard goes on it’s days, Leona Lewis would sing, “Keep bleeding, keep keep bleeding love <3″






Literature cited

Bateman, P.W., and P.A. Fleming. 2009. There will be blood: autohaemorrhage behaviour as part of the defence repertoire of an insect. Journal of Zoology. 278(4): 342-348

Berger , M., & Berger , G. (2009). 101 animal secrets. (1st ed., p. 45). U.S.A: Scholastic Inc.

Bruner, H. L. 1907. On the cephalic veins and sinuses of reptiles with description of a mechanism for raising the venous blood-pressure in the head. American Journal of Anatomy. 7:1-117.

Burleson, G. 1942. The source of the blood ejected from the eye by horned toads. Copeia  1942:246- 248.

Cowles, R. B. 1977. Desert journal: reflections of a naturalist. Univ. California Press, Berkeley

Heath, J. E. 1966. Venous shunts in the cephalic sinuses of horned lizards. Physiological Zoology. 39:30-35.

Middendorf G. A., III, and W. C. Sherbrooke. 1992. Canid elicitation of blood-squirting in a horned lizard (Phrynosoma cornutum). Copeia  1992:519-527.

Middendorf, G. A., III, and W. C. Sherbrooke  and E. J. Braun. 2001. Comparison of blood squirted from the circumorbital sinus and systemic blood in a horned lizard, Phrynosoma cornutum. Southwest. National. 46:384-387.

Schmidt, P.J., W. C. Sherbrooke, and J. O. Schmidt. 1989. The detoxification of ant (Pogonomyrmex) venom by a blood factor in horned lizards (Phrynosoma). Copeia 1989:603-607.

Sherbrooke,W. C. 1990. Predatory behavior of captive greater roadrunners feeding on horned lizards. Wilson Bull. 102:171-174.

Sherbrooke, W.C. and G.A.,Middendorf III . 2001. Blood-squirting variability in horned lizards (Phrynosoma). Copeia 2001:1114-1122.

Sherbrooke, W.C. and G.A. Middendorf. 2004.  Responses ofkit foxes (Vulpes macrotis) to antipredator blood-squirting and blood of texas horned lizards (Phrynosoma cornutum). Copeia 3: 652-658