Reptiles
Side-blotched Lizard
Uta stansburiana · also called common side-blotched lizard
The side-blotched lizard is easy to overlook: a small, dusty, common lizard darting off a desert rock. But its males play out one of the clearest examples in nature of a game with no winner, a three-way contest that cycles around and around like rock, paper, scissors.
Overview
Uta stansburiana is a small lizard, about 5 cm snout to vent, of desert, sagebrush, and dry grassland across the western United States and northern Mexico. It eats small invertebrates and is often the most abundant lizard in its range. Both sexes have a dark blotch behind each foreleg.
Three males, one loop
Males come in three throat colours. Orange males hold big territories and beat blue males, who guard one female. Blue males spot and repel the sneaky yellow males, who mimic females. Yellow males slip past the overstretched orange males. Each beats one and loses to another, so over the years the three types cycle in abundance and none stays on top.
Live fast
It matures in months, breeds in its first spring, lays several clutches, and most die within a year — so the strategies cycle visibly over just a few generations.
Status
Least Concern and extremely common, tolerant of disturbed land, though a few island and dune subspecies have tiny ranges.
Side-blotched Lizard: common questions
What is the rock-paper-scissors thing about side-blotched lizards?
In this species the males come in three genetically based types, each advertised by the colour of the throat, and each type does well against one of the others and badly against the third, exactly like the game. Orange-throated males are aggressive and hold big territories covering several females, and they can muscle out the blue-throated males, who defend just one female each. But blue males, by watching a single female closely, are good at spotting and driving off the yellow-throated males, who look like females and try to sneak matings. And the yellow males do well against the orange males, because an orange male spread thin over a large territory cannot watch every female, so the sneakers get past him. No strategy stays on top, and in long-term studies the three types cycle in abundance over the years.
How big is a side-blotched lizard and where would I see one?
It is small, with a body about 4 to 6 centimetres long and a tail roughly the same again, and a slender, flattened build. It is grey to brown, often speckled or with faint stripes, with the dark spot behind each foreleg that gives it its name. You would see it in dry, open country across the western United States, basking on a rock, a log, a fence post, or bare sand in the morning, then darting after insects. In much of the desert Southwest it is the lizard you see most often, active even on cool days when other species stay hidden.
Do females also come in different colours?
Yes, though it is less dramatic. Female side-blotched lizards carry a throat-colour system too, mainly orange and yellow forms, and it is linked to a trade-off in how they reproduce. Orange-throated females tend to lay larger clutches of smaller eggs, which pays off when the population is sparse, while yellow-throated females lay smaller clutches of larger eggs, which pays off when the population is crowded and competition among hatchlings is fierce. The frequencies of the two female types shift with population density from year to year.
How long do side-blotched lizards live?
Not long. It is a classic live-fast species. Eggs laid in spring hatch in summer, the young grow quickly, and they are ready to breed the following spring at less than a year old. A female may lay several clutches over a single season. Most adults die within about a year of hatching, from predation, cold winters, or simply the wear of a short intense life, and a lizard that reaches two years is old. This rapid turnover is part of why the throat-colour strategies can cycle so visibly over just a few generations.