It turns out there are fifteen species (with about the same number of subspecies), all in the genus Phrynosoma, meaning "toad-bodied." Of those, eight are native to the United States. The ones we likely see around here are (I'm pretty sure) the coast horned lizard, P. coronatum. It is a large species, reaching 4 inches in length (not including the tail), and is less rounded than other horned lizards.
I will quote a few interesting factoids from Wikipedia (since I'm tired* and don't have the energy to digest and regurgitate—apologies):
"The spines on the lizard's back and sides are made from 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)."
"Horned lizards use a wide 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."
"At least eight species [including ours] are also able to squirt an aimed stream of blood from the corners of the eyes for a distance of up to 5 feet. They do this by restricting the blood flow leaving the head, thereby increasing blood pressure and rupturing tiny vessels around the eyelids. Not only does this confuse predators, but the blood also tastes foul to canine and feline predators. It appears to have no effect against predatory birds."
Horned lizard populations have been seriously declining. When I was a child, I remember finding horned lizards quite often in the chaparral-covered hills around a home we lived in briefly. Nowadays, as I said, I feel very fortunate to see one.
"A University of Texas publication notes that horned lizard populations continue to disappear throughout the Southwest despite protective legislation. The Texas horned lizard has disappeared from almost half of its geographic range. Population declines are attributed to loss of habitat, human eradication of the ant populations upon which the lizards prey, displacement of native ant populations by invading fire ants [and, in California, by Argentine ants] (aided by synergistic effects of native ant eradication), and predation by domestic dogs and cats."
Here are a few more photos. All three of these are found in Arizona, in case you want a field trip.
|Texas horned lizard, P. cornutum|
|Regal horned lizard, P. solare|
|Flat-tailed horned lizard, P. mccallii|
* So tired that I seriously considered posting something to the effect of "Too tired to do anything but watch Easy Rider tonight, so that's what I'm going to do." Instead, you got to learn about horned lizards. Aren't you glad? And now I'm off to watch Easy Rider!