Rule 1: “Triangular heads”

Updated

In this lesson: why head shape is the single worst rule anyone uses, and a quiz that shows you.

[IMAGE SLOT C03-1 · Must show: a gophersnake flattening and flaring its head defensively · Original caption: “Harmless Great Basin Gophersnake exhibiting the common defensive display of head flaring, photo by Andrew Nydam” · Credit: Andrew Nydam · Lesson works without it: mostly]

In my informed opinion, head shape is by far the worst rule anyone could possibly use to determine if a snake is venomous or not. This commonly-used trick results in more harmless, beneficial snakes being killed than any other shortcut.

As we learned in the last lesson, this rule stems from the fact that vipers (such as rattlesnakes and puff adders) do have pronounced venom glands that make their head larger than their neck. However, most snakes can and do flare their necks out to look menacing as a defensive display. Plus, many snakes have heads that naturally have a triangular or diamond shape.

An experienced observer can indeed tell the difference between these subtleties, but a novice (meaning someone who is trying to use this rule) almost always mistakes the natural head shape of harmless snakes as being triangular. This is perfectly understandable, as snakes provoke fear in many people, and fear and adrenaline cloud our judgment. The result is almost always someone over-reacting and killing harmless, beneficial snakes. PLEASE DO NOT USE OR TEACH THIS “RULE.”

Here’s another way to see the problem. Without a sound basis of comparison, most snakes will appear to have a “triangular” head to the uninitiated. If you have never studied a watersnake’s head next to a cottonmouth’s, “triangular” is a word you will apply to both. The rule only works for people who already know the animals, and those people don’t need it.

A little head shape quiz

See if you can tell which of these snakes are venomous.

[IMAGE SLOT C03-2 — BLOCKED: this lesson does not work without it. Must show: a numbered six-photo composite of snake heads, all appearing ‘triangular’ or otherwise ambiguous, in this order: 1. Yellow-bellied Seasnake (photo by Myke Clarkson); 2. Western Ratsnake (photo by John Whitney); 3. Gophersnake (photo by Joe Graves); 4. Eastern Hog-nosed Snake (photo by Tim Spuckler); 5. Florida Watersnake (photo by Kaylynn McKathan); 6. California Red-sided Gartersnake (photo by Tim Spuckler). · Original composite had no separate caption; the numbered answer key below carries the credits. · The whole point of the quiz is that the reader looks at photographs and gets it wrong; do not replace with text.]
Answers (don’t peek until you’ve decided)
  1. VENOMOUS Yellow-bellied Seasnake, photo by Myke Clarkson
  2. HARMLESS Western Ratsnake, photo by John Whitney
  3. HARMLESS Gophersnake, photo by Joe Graves
  4. HARMLESS Eastern Hog-nosed Snake, photo by Tim Spuckler
  5. HARMLESS Florida Watersnake, photo by Kaylynn McKathan
  6. HARMLESS California Red-sided Gartersnake, photo by Tim Spuckler

Two through six are all perfectly harmless snakes that illustrate how nonvenomous snakes often have a triangular appearance. The first snake, indigenous to tropical seawaters (and occasionally reaching as far north as southern California), is the only venomous snake in the quiz and it has a slender head. Hopefully, you’re able to see why so many people are so often mistaken when using “triangular heads” as a rule. If you’re not convinced, an identification group will show you hundreds more examples (see Where to get an identification).

Take this further

  • A sentence that works out loud: “Any snake can flatten its head when it’s scared. That’s a scared snake, not a venomous one.”
  • Next: Rule 2: “Cat eyes”.
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