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Fence swift, Sceloporus undulatus
Photo © 2005 Jim Jung and licensors. All rights reserved.

Fence Swifts

Sceloporus undulatus

The rough, spiny Fence Swifts are one of the most common lizards in our area. If you walk softly and quietly through upland woods you can often hear them scurrying across tree trunks and rocks in an effort to keep a safe distance between themselves and you. But unlike most animals they seldom disappear but instead peek out from their hiding places to stare curiously at you.

Fence Swifts, being fairly large and easily viewed lizards, are one of the better studied species in our fauna.

Fence Swifts, Sceloporus undulatus
Photo by Jim Jung. All rights reserved


Female Fence Swifts excavate a small hole in soft, well-drained upland soil that receives some sunlight and deposit up to eighteen small, rubbery, nearly round eggs. A well-established and mature female often lays two clutches of eggs per year. After covering and smoothing the soil over the eggs she returns to her territory and leaves the eggs to their fate. The young Fence Swifts - miniature versions of the adults in nearly every detail - emerge in early September and remain together until October when they disperse and enter hibernation in a hollow log or abandoned mouse burrow. They can most commonly be found on logs, rocks and tree trunks on sunny afternoons soaking up rays in upland forests and clearings. Like all baby animals these little lizards will often allow you to get quite close before scampering away to safety.


Those who manage to survive their infancy eventually find a small patch of ground where they establish a home range of around a hundred square feet and live out their brief two to three year life span. Here these alert reptiles know every branch, hole, rock and leaf intimately and here they seek out their prey of small beetles and other insect food, dodging birds and snakes intent on making a meal of them.

Male Coloration

The young grow swiftly and once adult size is reached (about six inches in total length) the males develop patches of intense blue on their sides to advertise their status. Should another fence swift trespass on their turf the two lizards will engage in a series of head-bobbing pushups in order to establish dominance. The more drably colored females also exhibit this behavior. At breeding time the males develop bright pink or reddish patches on their cheeks and throats.

Missing Tails

One often encounters lizards with short and discolored tails. These are individuals exhibiting regenerated tails who lost their originals to a predator. Like nearly all of our lizards the fence swift has a detachable tail that continues wriggling for some time after it's removed. This wriggling bit of lizard flesh distracts and confuses the predator and allows the lizard to escape. Tails that are the regenerated are always a different - usually darker - color than the rest of the lizard.

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The information on this page is tailored to Southern Illinois, Southwest Indiana, Western Kentucky, and Southeast Missouri

Copyright © 2005 Jim Jung. All rights reserved
Some images on this page copyright © 2004