Horned lizards have an unusual fallback when camouflage fails: they can squirt foul-smelling blood from around their eyes. But the defense is not universal, and it cannot protect the animals from the habitat changes and invasive fire ants threatening some populations in Texas. Those limits are central to a Popular Science report by RJ Mackenzie, which draws on comments from Texas Christian University biologist Dean Williams and describes a possible link between the lizards’ diet and the taste of their blood.
Williams studies horned lizards in central Texas. He told Mackenzie that the animals first rely on crypsis, or blending into their surroundings. Their sand-colored, spiny backs can help them disappear among rocks and scrub. Even when researchers use radio trackers to narrow a lizard’s location to an area about the size of an office desk, Williams said, finding it can take about 15 minutes of searching.
If hiding fails, some horned lizards can release blood from vessels around their sinuses. Williams explained that pressure builds until the vessels burst, sending blood outward in jets. The report says mammals exposed to the stream react with disgust. One experiment also illustrates a possible cost: a lizard lost 6.8 percent of its body mass after squirting blood when exposed to a dog. That single reported case does not establish how much blood lizards typically lose or how often the defense is used.
The blood’s foul taste may be connected to a key food source. Horned lizards eat large numbers of harvester ants, whose venom causes intense, long-lasting stinging pain in mammals. Mackenzie points to a 2024 study in which a compound in lizard blood rose after scientists fed the animals harvester ants. The researchers propose that the compound, possibly adapted from ant venom, makes the blood taste unpleasant. The report does not identify the compound or establish that proposed origin, so the connection remains tentative.
The defense also varies with the predator. According to Williams, birds of prey can still eat horned lizards; the lizards may use the horns on the backs of their heads to jab at birds trying to seize them. Blood does little to deter snakes either. The report describes different responses: lizards may flee rattlesnakes, which wait for prey to approach, while flattening their bodies against the ground can make them harder for pursuing coachwhips or racers to swallow. These examples show that the blood is one part of a broader set of defenses, not a shield against every predator.
For Texas populations, the larger challenge is habitat. Mackenzie reports that horned lizards have disappeared from habitat across eastern Texas. Williams links population declines to industrialization and says the lizards are sensitive to habitat changes. In towns where brush is cleared, he said, lizards disappear. Because horned lizards are ectotherms, the report explains, they rely on behavior to regulate body temperature; without the cool shade of vegetation, Texas summer heat can leave them unable to keep their bodies within safe limits.
Fire ants add another pressure. The report says these invasive ants swarm ground-dwelling lizard nests, eat vulnerable eggs, and can attack or kill young lizards. A conservation program involving zoos across Texas releases nearly a thousand young lizards each year, according to Williams. His graduate student Kira Gangbin is working on a targeted poison to reduce fire ant numbers and help hatchlings survive. The report describes this as ongoing work, not a demonstrated solution.
The story’s central lesson is that a striking defense can help an animal cope with some immediate threats while leaving it vulnerable to changes in its surroundings. For horned lizards, camouflage and blood-squirting may complicate encounters with predators, but preserving brush habitat and protecting young lizards from fire ants are separate conservation challenges.
<a href="https://www.popsci.com/environment/why-horned-lizards-squirt-blood-from-eyes/">Source: Popular Science report</a>