Western fence lizard

The blue-bellied lizard of West Coast rock walls and fence rails, whose blood carries a protein that kills the Lyme disease bacterium inside a feeding tick.

Western fence lizard at a glance

Sceloporus occidentalis Sceloporus occidentalis is SEL-oh-POR-us ok-si-den-TAL-iss

Type
Reptile · lizard
Diet
Insectivore
Size
Nose to tail it runs about as long as a new pencil, around 8 inches / 21 centimeters, and more than half of that is tail. Body length alone, snout to vent, is 2.2 to 3.5 inches / 5.7 to 8.9 centimeters.
Lifespan
Commonly cited as roughly 5 to 7 years in the wild.
Conservation
Least concern

Eats beetles, spiders, ticks, crickets, isopods, centipedes

It suns on a rock, log, or fence rail, then darts out to grab a beetle, spider, or tick and swallows it whole before going back to basking.

Should you worry?

It has no venom. Like many lizards, it may bite if someone grabs it, and the small teeth can break the skin. It will dash off a rock long before anyone gets close. The one indirect thing worth knowing: because ticks that bite this lizard often lose the Lyme bacterium in the process, still do a tick check after time in tall grass. Not every tick meets a lizard first.

Every warm rock at Redwood or Lava Beds seems to have one doing push-ups: a lizard about as long as a new pencil, gray-brown and blotched, snapping upright to flash a throat the color of a gas flame. That’s a male western fence lizard defending a patch of fence rail or rock from a rival, and the flare of blue along his throat and belly is why almost everyone here calls him a blue-belly.

The color is a display, but the blood underneath does something stranger. In 1998, a University of California, Berkeley study found a protein circulating in this lizard’s blood that kills Borrelia, the bacterium that causes Lyme disease. A tick that bites a western fence lizard to feed often loses the infection it was carrying, cleaned out mid-meal by the lizard’s own blood.

Lyme disease shows up far less often on the West Coast than in the woods of New England, and this lizard’s blood is one reason researchers point to. It doesn’t clear every tick, so a hike through tall grass still calls for a tick check afterward. But the next blue-belly doing push-ups on a sunny boulder is doing that work anyway, one tick at a time.

Did you know?

  • A 1998 UC Berkeley study found a protein in the western fence lizard's blood kills the bacterium that causes Lyme disease, so a tick that feeds on this lizard often loses its infection.
  • Lyme disease is far less common on the West Coast than in the Northeast, and this lizard's blood is one reason researchers point to.
  • Males defend territory with blue throat and belly patches, doing push-ups and head-bobs to warn off rivals each spring.

Common questions

Are western fence lizards poisonous, and do they bite?

They are not poisonous or venomous, but yes, one may bite if you grab it. UC IPM says many lizards try to bite when handled roughly, and their small, sharp teeth can break the skin. Left alone, it runs from people and is gone before you get close.

Why is it called the "blue-belly"?

Males have patches of blue on their throat and belly that they flash while doing push-ups to defend their territory.

Can this lizard really help stop Lyme disease?

A protein in its blood kills the Lyme bacterium inside a tick that bites it, so the tick is often cured rather than staying able to spread the disease.

What does a western fence lizard eat?

Small invertebrates: beetles, spiders, crickets, and ticks, mostly caught by waiting on a warm rock and darting out.

Where it lives

Where we got this