According to my research, there are four types of snakes found in Wisconsin with orange bottomed bodies. These are: Clonophis Kitlandii, Crotalus Horridus, Diadophis Punctatus, Storeria Occipitomaculata and Thamnophis Sirtalis. Of these, the Diadophis Punctatus, also known as the ring-necked snake, has a behavior closely matching to the given description as it usually warms itself under rocks exposed to the sun. The ring-necked snake feeds on small salamanders, lizards, frogs, earthworms and juvenile snakes of other species. Moreover, it does not pose any threat to humans. If you remember more details about the snake you saw, you can also match it with information on www.discoverlife.org.