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Q: Pupil shape for non-venomous snakes
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I have maybe a dumb question....... I have been hearing that you can tell if a snake is venomous by the shape of the pupil, round is non-venomous, cat shape is venomous. But it seems to me there are non-venomous snakes with cat shaped pupils. Can someone clear this up for me?

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Topics: Eyes
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Accepted Answer 11/6/2010 9:14:15 AM

Not a dumb question at all! Eyes are never a great way to tell if a snake is venemous or not. Coral snakes for instance and their mimics both have "round" eyes, so unless you new the Phenotypical differences you would not know the difference. Most Colubrids such as rats, garters, beauty, hognoses, and king snakes are non-venemous with "round" eyes, but one snake in the family, a boomslang is fast and highly venemous and kills many people every year, again it has "round" eyes. We had a viper boa for a long time which mimics the look of a water moccasin. It has cat eyes and a huge triangle head like most your venemous snakes, but is non-venemous. As far as Alabama goes, all the venemous native species do sport the "cat" eye. So unless you know for sure the species you are looking at in the wild it is usually A good rule of thumb not to mess with any snake your unsure of, or photograph the animals in question and do reasearch or ask an experienced snake person (like us on here!). You took a good step to contact people to learn more, just be sure to always do your reaserch before every purchasing animals to learn about everything from husbandry to eyes and venom and you will be A-ok! 
Member Comment 11/6/2010 9:43:22 AM

If you are close enough to see the pupils and you're not sure if it's venomous, you probably have other things to worry about!

But no, pupil shape is not a reliable way to tell if a snake is venomous or not.  If you're concerned about local species, pick up a field guide to see what's in your area.  We don't have much by the way of venomous types of snakes in North America, and there's only a small handful that don't rattle.  :)
Member Comment 11/6/2010 10:38:26 AM


Non-venomous Green Tree Python.
Member Comment 11/6/2010 11:52:59 AM

Aaron, i know you have at least one venomous GTP over there. Lemme see it!
Member Comment 11/6/2010 12:27:04 PM


Some non-venomous colubrids have cat eyes like the cateye snake (actualy rear fanged) also other rear fanged colubrids like vine snakes, lyre snakes, and  night snakes just to name a few. There are also some purely non-venomous snakes like the house snake,african tigersnake and egg eating snake with virtical pupils. also many boas and pythons have cat eyes and most (if not all) elapids like cobras or coral snakes lack  cat eyes. the cat eyed snake rule is more about vipers witch are the classic virtical pupiled snake. So the rule is untrue In some places, though east of the missisipi river there are no non-venomous snakes with cat eyes ( in the western us there are night and lyre snakes). I think you also have to be very close to a snake to tell its eye shape.

Member Comment 11/6/2010 12:35:31 PM

Sonja K. Reptiles
I thought pupil shape was just more or less an indicator if the are diurnal or nocturnal.
Member Comment 11/7/2010 1:32:17 AM

Katie M

I believe that this is coming up because of Billy the Exterminator or Bob the Exterminator or something of the like.  If he had things accurate, I could quote him and say that "my ball python is poisonous"

(thank you Heather :)

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