Milk snakes are harmless colubrids, while coral snakes are venomous elapids. Because of similarities in color and pattern, the two animals are easily mistaken for one another.
Coral snakes and some species of milk snake exhibit bold rings of color in red, black and yellow. There are three species of coral snake in the United States: Eastern, Texas and Arizona. All three have black heads with small eyes. The notable feature of coral snake coloration is that red bands touch yellow bands, prompting the common phrase, "red on yellow, kill a fellow." Coral snakes, along with cobras and mambas, are elapids. Like most elapids they possess a potent neurotoxic venom that attacks the nervous system. Fortunately, coral snakes are shy animals that are hesitant to bite unless provoked. Since the advent of coral snake antivenin, there has been only one recorded human fatality, which occurred because the individual did not seek medical attention for the bite.
Milk snakes, along with garter snakes and rat snakes, are colubrids and are completely harmless to humans. Milk snakes, depending on the species and geographic location, come in a vast array of colors and patterns. The vibrant red, black and yellow varieties of milk snakes and kingsnakes resemble the venomous coral. Some milk snakes, like corals, have a black head. However, the red bands of the milk snake touch the black bands rather than the yellow, leading to the useful phrase, "red on black, friend of Jack."