Commonly confused: bullsnake and rattlesnake

Let’s begin by laying down some facts that we can sink our teeth into! There are very few species of snakes in Colorado that are considered dangerously venomous, which means that chances are that the snake you encounter next will be non-venomous, i.e., harmless to humans. Of the 30 or so species of snakes in Colorado, the good news is that only three are dangerously venomous! These three venomous snakes happen to be all rattlesnakes, but there tends to be a substantial amount of confusion in distinguishing rattlesnakes from other non-venomous snakes, despite all the information available. For example, the snake most commonly confused with rattlesnakes is the bullsnake, and this confusion transcends generations with repeated inaccurate information. Whether a newly hatched baby, juvenile, or adult, the myths associated with bullsnakes vs. rattlesnakes are clearly entrenched.

Let’s examine just a few commonly repeated myths for clarification. The first one states, “If the tail is rattling, it’s a rattlesnake”! Typically, all snakes vibrate or rattle their tail for different reasons. Usually, it happens when the snake is feeling threatened and wishes to either scare the offending threat away or, if an attack ensues, hopefully the tail will attract the brunt of the attack, and leave the head unscathed. In this way, the snake is more likely to escape with its life. If the tail vibration occurs in dry leaves or against an object that reverberates, the sound is amplified and may, in fact, mimic the rattle vibration of a rattlesnake. Watching the tail vibrate, you may notice that it is held close to horizontal in non-venomous snakes, while rattlesnakes tend to hold their tail vertically. It’s important to note that with rattlesnakes, the tail tip is usually composed of a series of segments or rattles that move when the tail tip is vibrated, creating that well known rattlesnake sound! Baby rattlesnakes only have one segment on their tail tip at first, so no sound is emitted, but the tail is still usually held vertically. In addition, rattlesnake tails are short and blunt, ending with rattle segments, while the tail in non-venomous snakes is long, with a gradual taper to only a sharp point.

The second popular myth states, “Bullsnakes can breed with rattlesnakes, creating venomous bullsnakes”. When we look at the biology of this situation, we realize this event could not possibly happen, because bullsnakes are egg layers, and rattlesnakes give birth to living young, like mammals. It just doesn’t work!

The third popular myth relates to a concept that states, “Bullsnakes chase away rattlesnakes”. Again, in looking at how these two snake species live out their lives in the same habitat, one can see that they go about life’s needs in entirely different ways, which reduces conflict and competition, allowing both snakes to co-exist. This concept may have had its origins in observing when both species occur together. Both are seen in the spring, but as the summer progresses rattlesnakes become more nocturnal, while bullsnakes may still be active when it’s not too hot. Separation of activity times may leave us with the impression that bullsnakes have indeed “chased” the rattlesnakes away!

There are several other myths, but the myths described are the most often quoted. It may useful to note that bullsnakes are not typically snake eaters, so they would not have any influence on rattlesnake populations. So, just how does someone identify a bullsnake (or other non-venomous snake) from a rattlesnake? Because many snake species have a pattern of somewhat rounded or square-shaped, dark designs on their backs, including rattlesnakes and bullsnakes, this patterning is not a reliable identification tool. Instead, look at the tail and head. We have already discussed the tail differences, so let’s focus on the head. Bullsnake head shapes are barely triangular unless the snake is hissing at you (you’re too close!), while the neck width is nearly the same as the base of the head width. Much like looking at your thumb! Rattlesnakes have a strongly triangular head with a much thinner neck width relative to the base of the head. Moreover, each side of the rattlesnake’s face we find a pair of horizontal white stripes, akin to war paint! In addition, rattlesnakes tend to adopt a tight coiled posture at rest, different from other snakes.

With the tail and head shape in your focus, you should be able to make a pretty reliable identification of whether the snake is a rattlesnake or not. As always, stay at least 3 feet away from the snake until you’re sure about your identification, still giving the snake some space, regardless.

Bullsnake, photo by Matt Cage

Prairie Rattlesnake, photo by Matt Cage