Lizard behavior can be influenced by ultimate forces such as adaptation and phylogeny, and proximate forces such as temperature and rainfall. Italian wall lizards (Podarcis sicula campestris) were successfully introduced into two locations in the USA, both at latitudes similar to their probable sources in Italy. Behavioral differences between native and introduced populations are likely due to proximate forces. From 1999–2000, we documented the seasonal and diel behavior of wall lizards in New York. We observed a bimodal activity pattern during the summer and a unimodal activity pattern in spring and fall, which has been reported for native populations in Italy. Unlike Italian populations, New York lizards were completely inactive during winter months, which is probably due to the much lower minimum winter temperatures in New York.