Photo © Andrew McInnnes
Hiding in Plain Sight
The lesser-known round-tailed horned lizard uses camouflage to look like a rock.
By Charles Jacobi
A lizard seldom seen and sometimes sought after by enthusiasts, the round-tailed horned lizard is a lesser-known cousin of the Texas horned lizard that we all know and love. It’s likely that if you’ve done some outdoor exploring in the Trans–Pecos, you’ve stepped right over one.
No surprise that this lizard’s name comes from its tail, rounded on the end (with dark banding along its length). Up close, the tail easily distinguishes the round-tailed horned lizard from our other two Phrynosoma lizards: the Texas horned lizard and the greater short-horned lizard. Its habitat can be described as desert–scrub or arid grasslands with sandy soils and lots of pebbles. The round-tailed horned lizard is diurnal (active during the day) and can be found in open flat areas in the spring and early summer. This lizard likes it warm, though when summer temperatures are too much to bear, they’ll seek shady areas under cover.
The round-tailed horned lizard (Phrynosoma modestum) measures 2 to 6 inches long and varies in color. The base color can be light gray or brown, even a bleached yellow, with a pale underside. It lacks the enlarged scales that border the abdomen and dorsum like other Phrynosoma, and has four smaller, conspicuously aligned horns behind the head.
The most interesting thing about the round-tailed horned lizard? It utilizes eucrypsis, or concealment through coloration or pattern, to appear as a stone or pebble. Behavioral studies show that round-tailed horned lizards flee from predators sooner in sandy areas compared to rocky ones, indicating the lizards may be aware they’re more visible in these areas. The lizard relies on this amazing mimicry to avoid predation, while other lizards rely on speed and evasion.
Round-tailed horned lizards start their breeding season in spring, after their winter emergence. Clutches of five to 12 eggs are laid in burrows excavated by the lizard. Females have been observed guarding these nests, butting and biting at predators that approach. Their diet consists primarily of ants, though they also consume beetles, termites and butterfly and moth larvae.
If you encounter a round-tailed horned lizard, submit your observations to theon iNaturalist.