Red and Black, Stay Back Jack

Some of you may have heard the warning "Red and black, stay back, Jack!" or some variation of it. This warning is of course used as a basis of what snakes may or may not be poisonous, but that isn't always true. When I was presenting the gentle, Nelson's Milksnake, I was asked by a student "Isn't that poisonous?" Of course I knew that it wasn't, but I couldn't fully explain why the rule didn't apply to milksnakes. Lucky for us 'Mericans, most of the snakes that live in the U.S. are nonvenomous. However, the exceptions include water moccasins, copper heads, coral snakes, and rattle snakes. Is there any way we can tell a harmless milksnake from a deadly coral snake?
Here are a few rules of thumb:

1) Snakes that have a broad triangular head, such as Vipers and Cotton Mouths, are likely to be poisonous.
2) If they are large and chubby, they are likely to be dangerous.
3) Most venomous snakes require hot and humid climates (so you won't find many in Michigan). But you may need to be more conscious in warmer climates.

IF YOU ARE ABLE TO GET CLOSE:  (Not recommended)
1) Snakes with slit eyes (like cat eyes) are possibly poisonous.
2) Snakes with a raised nose or pointed nose are likely poisonous
3) Heat seeking sensors are common traits of poisonous snakes due to their hunting techniques. These can be found between the eyes and nostrils.

It is important to remember that there are exceptions to all these rules. Snakes like coral snakes are highly venomous, but don't have slit eyes and are usually thin, while the harmless Jungle Carpet Python does have slit eyes, but is nonvenomous. The best thing to remember is to stay away from any wild snakes. While they may not be poisonous, they are still wild and probably have aggressive tendencies.
Links: http://animals.howstuffworks.com/snakes/how-to-know-if-snake-is-poisonous.htm
http://www.snake-removal.com/venomous.html

Deadly Coral Snake

Harmless Milksnake