Horned Lizard Squirting Blood: The Secret of the Spiny Reptile

Sherbrooke, W. (2012). Negative oral responses of a non-canid mammalian predator (Bobcat, Lynx rufus; Felidae) to ocular-sinus blood-squirting of Texas and regal horned lizards, Phrynosoma cornutum and Phrynosoma solare. Herpetological Review, [online] 43(3): 386-391. Available at:

The horned lizard defense flow chart uses the following images of their predators:Chihuahuan grasshopper mouse by American Society of Mammalogists (CC BY 2.0)Rattlesnake by Ann W (CC BY 2.0)Sonoran Coachwhip snake by Andrew DuBois (CC BY-NC 2.0)Roadrunner by Teddy Llovet (CC BY 2.0)Coyote by Larry Lamsa (CC BY 2.0)

Horned Lizard Squirting Blood

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The short-horned lizard is a one-reptile wrecking crew with a bizarre self-defense strategy. When defending its own life, this lizard squirts blood from the thin blood vessels around its eyes that rupture under pressure.

The generic name Phrynosoma means "toad-bodied". In common with true toads (amphibians of the family Bufonidae), horned lizards tend to move sluggishly, often remain motionless, and rely on their remarkable camouflage to avoid detection by predators. They are adapted to arid or semiarid areas. The spines on the lizard's back and sides are modified reptile scales, which prevent water loss through the skin, whereas the horns on the head are true horns (i.e., they have a bony core). Of the 21 species of horned lizards, 15 are native to the USA. The largest-bodied and most widely distributed of the American species is the Texas horned lizard.

Horned lizards use a variety of means to avoid predation. Their coloration generally serves as camouflage. When threatened, their first defense is to remain still to avoid detection. If approached too closely, they generally run in short bursts and stop abruptly to confuse the predator's visual acuity. If this fails, they puff up their bodies to cause them to appear more horned and larger, so that they are more difficult to swallow.[1]

While previous thought held that compounds were added to the blood from glands in the ocular sinus cavity, current research has shown that the chemical compounds that make up the defense are already in the circulating blood.[3][4] It is possible that their diet of large quantities of venomous harvester ants could be a factor; however, the origin and structure of the chemicals responsible are still unknown. The blood-squirting mechanism increases survival after contact with canine predators;[4] the trait may provide an evolutionary advantage. Ocular autohemorrhaging has also been documented in other lizards,[6] which suggests blood-squirting could have evolved from a less extreme defense in the ancestral branch of the genus. Recent phylogenic research supports this claim, so the species incapable of squirting blood apparently have lost the adaptation for reasons yet unstudied.[7]

To avoid being picked up by the head or neck, a horned lizard ducks or elevates its head and orients its cranial horns straight up, or back. If a predator tries to take it by the body, the lizard drives that side of its body down into the ground so the predator cannot easily get its lower jaw underneath.[citation needed]

A University of Texas publication notes that horned lizard populations continue to disappear throughout their distribution despite protective legislation. Population declines are attributed to a number of factors, including the fragmentation and loss of habitat from real estate development and road construction, the planting of non-native grasses (both suburban and rural), conversion of native land to pastureland and agricultural uses, and pesticides. Additionally predation by domestic dogs and cats place continued pressure upon horned lizards.[8]

Fire ants (Solenopsis invicta) introduced from South America via the nursery industry's potted plants, pose a significant threat to all wildlife including horned lizards. Phrynosoma do not eat fire ants. Fire ants kill many species of wildlife and are fierce competitors against native ants which horned lizards require for food (with their specialized nutritional content). Fire ants have given all ants a bad reputation and human attempts to eradicate ants, including invasive species and the native species on which the lizards prey, contribute to the continued displacement of native ant species and decline of horned lizards.[8]

The Texas horned lizard (Phrynosoma cornutum) has disappeared from almost half of its geographic range. Their popularity in the early to mid 20th century pet trade, where collectors took thousands from the wild populations to sell to pet distributors, without provision for their highly specialized nutritional needs (primarily formic acid from harvester ants), resulted in certain death for almost all the collected lizards. In 1967 the state of Texas passed protective legislation preventing the collection, exportation, and sale of Phrynosoma, and by the early 1970s most states enacted similar laws to protect and conserve horned lizards in the USA. However, as recently as the early 2000s the state of Nevada still allowed commercial sale of Phrynosoma. Despite limited federal protection in Mexico, horned lizards are still offered in Mexican "pet" markets throughout the country.[8]

In 2014, the Center for Biological Diversity in Tucson petitioned the Oklahoma Department of Wildlife Conservation to have the Texas horned lizard put on the endangered species list due to the massive declines of its population in Oklahoma, where it was once plentiful. The center said it may later seek protection for the animal on a federal level; it also said that reptiles in general are dying off at up to 10,000 times their historic extinction rate, greatly due to human influences.[9]

The genus of horned lizards is the official state reptile of Wyoming.[11]Texas designated the Texas horned lizard (Phrynosoma cornutum) as the official state reptile in 1993[12] and the "TCU Horned Frog" is the mascot of Texas Christian University in Fort Worth, Texas. TCU is the only known athletic team with the horned lizard as a mascot.

UPDATE: It would appear that whatever the effect of the blood-spurting eyes on mammals, the American kestrel is unimpressed. This photo by John Roser shows over 30 horned lizard skulls that were found while clearing out a kestrel nestbox (h/t @ftcreature on Tw*tter)

Watch out - They Squirt Blood! If threatened by predators, horned lizards will squirt blood from the eyes. The squirting blood comes from ducts in the corners of their eyes and can travel a distance of up to three feet (one meter). It's meant to confuse would-be predators including birds, coyotes and snakes. The photo shows an adult with blood around the eyes.

They are the only species of horned toads that give birth to the young live. Other species of horned lizards lay eggs. In the Short-horned lizard, the eggs are retained within the mother until the live young are born.

Did you know? Short-horned Lizard adults weigh less than a quarter. A yearling is about the weight of a dime. They give birth to the young live. Predators include snakes, magpie, ravens, and hawks. Horny toads like to eat ants and beetles. Short-horned Lizards will shoot blood from their eyes when threatened by a predator.Short-horned Lizard, female with her young

If harassed by a potential predator, this lizard can build up enough pressure behind its eyes to squirt a stream of blood mixed with noxious biochemicals in the face of the predator. This foul-tasting concoction is often enough to ward off anything thinking about eating the lizard.

In addition to this unique defense mechanism, the Texas horned lizard has a fairly robust spiny appearance. This can also deter predators. These defenses are especially needed because of its mostly sedentary lifestyle which leaves it vulnerable to predation.

This horned lizard was found in southeast Colorado in the Comanche Grasslands National Preserve. Preserves such as this one allow for the native wildlife to thrive in a relatively undisturbed habitat.

It's pretty easy to see how the short-horned lizard got its name, but these spiky reptiles have more in their defence arsenal than a bit of body armour: when threatened, they can shoot blood out of their eyes!

Also known as "horny toads" because of their flattened shape, short-horned lizards (Phrynosoma douglassi) employ the blood-shooting only as a last-ditch effort. The salvo comes from ducts located near the eyes, and it's blood with a bonus: in addition to the usual components, research shows the foul-tasting fluid also contains chemicals that cause gastric distress in some animals (and that's something members of the genus who don't shoot blood can't boast about).

All that said, blood-squirting is a last resort, and the reptiles very rarely squirt humans. Horned lizards more commonly turn to a different tactic to scare off would-be predators like hawks, coyotes and snakes: looking large and in charge. The lizards can nearly double in size by inflating their bodies!

There are 14 different species of horned lizards that exist around the world. Some of them include the Texas horned lizards, short-horned lizards, desert -, coast -, regal -, and mountain horned lizards. The male lizards are known to vigorously bob their heads at females to call and attract them during the mating season. These lizards are also well-known for squirting blood from their eyes.

Two rows of the horns or spikes run along the lateral portions of their torso and separate the larger spikes on their dorsal side from their scaly underbelly. The snout-vent length of the Texas horned lizards, for instance, measures about 69 mm after they reach sexual maturity, which is around 13 months old. 2ff7e9595c