Per the website Wild Snakes Education and Discussion, the ages old rhyme should be taken with a grain of salt.

The rhyme goes “Red touches black, venom lack. Red touches yellow, kill a fellow”. There are a few other variation of this rhyme, but the idea behind it is to identify these snakes by the color of their banding. Several species of non-venomous snake in the U.S. have alternating red, black, and yellow banding and have historically caused confusion.

Here are the four “controversies”:

The first controversy is that sometimes (rarely) a snake will be found that does not look like the field guide photo. These snakes are called “aberrant” and they often have markings and colors that are different – sometimes extremely different – from the “normal” version of the species.

The second controversy is the existence of a snake native to the southwestern U.S., the Shovel-nosed Snakes (Chionactis sp.) These small, harmless snakes do have red and yellow bands touching, which may cause confusion and could result in these snakes being killed.

The third controversy is that the rhyme is often misquoted and mixed up which could cause someone to mistake a coralsnake for a non-venomous species.

The fourth, most dangerous, and 100% accurate argument is that the rhyme is only reliable when in reference to coralsnakes native to the United States. Once we enter Mexico and down through South America, we encounter dozens of coralsnake species which do not follow any rules or rhymes. To add to the confusion there are also dozens of coralsnake “mimics” in Central and South America and Mexico. These range from non-venomous species to rear-fanged and venomous species.

Go, now, read the whole article… it just might save your life. Link