Western fence lizard

A western fence lizard perched on my hand. Image taken in the San Francisco Bay Area.

If you enjoy hiking and live on the west coast of the United States, chances are you have come across this little lizard. This is a western fence lizard, which is also known as a “blue belly.” Blue belly is a good nickname for this lizard because…well, look:

Western fence lizard belly

A western fence lizard showing why they have earned the nickname "blue bellies." Image taken in the San Francisco Bay Area.

They do actually have blue bellies. The males are generally more blue than the females and will flatten to flash their blue when potential mates approach. When they are mating, some of the brownish scales will also turn bright blue. The only problem with the nickname blue belly is that there are a few species of lizard that have blue bellies, so it can get confusing.

Anyway, both female and male western fence lizards create a territory and they return to the same area year after year to reclaim it. This happens in the spring, which is a really good time to stop and watch them; this is when a lot of their interesting behaviors happen. While establishing their territory, they’ll posture and mark the area with chemical cues. Breeding males with do push-ups to try and attract females. If they succeed, they’ll bite the female’s neck and mate with her. If the female changes her mind however, she’ll flip over and use all four feet to kick the male off of her.

But aside from being entertaining, these little lizards that you see running around all of the time also provide a wonderful service for hikers, in what is probably the coolest animal fact I have uncovered since the photosynthesizing sea slug. Here’s what it does:

A tick on western fence lizard

A tick feeding on a western fence lizard. Image taken in the San Francisco Bay Area.

That lump on its neck is a tick. (Notice the lizard in the second picture has two, one on each side) The western black-legged tick is the main vector of Lyme disease for humans in our area. However, the blood of a western fence lizard has a protein in it that kills the bacteria that causes Lyme disease. If one of these ticks feasts on a western fence lizard, it becomes “disinfected.” If it had the offending bacteria, it no longer does and can no longer cause disease in humans! What’s more, these ticks, especially the nymphs, love to feast on fence lizards. The overall result? In areas that are not lucky enough to have these lizards around, about half of these ticks carry the Lyme disease causing bacteria. Where there are western fence lizards, that percentage drops to between 1 and 5%. Even if we get bitten by the right species of tick, the likelihood of getting the disease is really low.

When I find out about something as unlikely as this, it always reminds me that we are a part of an overall balance and cannot possibly know the effects of removing one species from it. So many factors like this crisscross in ways we have yet to uncover. Before the late ’90s, when this was discovered, who would have guessed that if the western fence lizards were to disappear, we could face an increase in cases of Lyme disease? Or that their blood would have a Lyme disease-bacteria-killing protein in it? And how awesome is that!

Anyway, thank you western fence lizard; your sacrifice is much appreciated.