How do you tell the sex of a lizard or snake?

Searched for this on internet… are there pictures out there? I am assuming reptiles keep sex organs inside their body… but then how do you tell the sex??? Does it take a pHD degree or what? Would really like to know…(I currently have a freshly caught tree lizard, the grey kind, and it is really fat…wondering if it is pregnent?:confused:

It can be difficult with some species ( and some individuals ). The surest way is to use a blunt probe to gently check the genital opening for the presense or absense of hemipenes ( the male intromittent organ in snakes and lizards ).

However once you have some experience, you can often tell by looking for the presense or absense of a tell-tale swelling near the base of the tail. If present, you have a male. 'course this only works with mature individuals, is not 100% accurate, and requires both experience ( preferrably with that particular species ) and a good eye.

Also many species have a marked external sexual dimorphism, be it color, size of the head, or what have you. But this is very species-specific of course.

  • Tamerlane

ok… that’s helpful… This lizard I have is fat… and the sex slit in it’s tail is (at first look) oozing white_yellow pus stuff… according to your response… this is a male?..because of swollen glands? Is this right?

Okay with Tree Lizards in the genus Urosaurus, the male has three blue patches. One centered under the throat and another on each side of the belly. Both males and females should have pale yellow or orange at the throat as well.

Where in Texas did you catch it? There are a couple of different species.

  • Tamerlane

Well, this is very Texas, but caught him/her on a Mesquite tree…which grow really big around here… and have all sorts of ants and other insects roaming around on the bark… old folks around here call these lizards “mountain boomers” but this confuses me too as we have no mountains anywhere around here?

Ehh…Not necessarily, though possibly. And the glands aren’t swollen per se, you would just be seeing the normal bulge of the hemipenes if it were a male. The “fat” part might be a good sign that it’s a gravid female. In fact if it is tiny enough and you carefully hold it against a background light source, you might be able to see the outlines of eggs. Won’t work if it is too bulky, though.

I have to run because company just came in, but I’ll check back later and see if you’re still having difficulty :).

  • Tamerlane

ok…I understand but this is a lizard 8in long…I don’t think the light thing is going to work

Wait, wait, wait…what do you mean this lizard is oozing some sort of pus? Is it peeing, do you know? 'Cause lizard pee is not like human (mammal) pee- they actually excrete liquid waste as uric acid crystals which look whitish-yellow and can be very thick and goopy. (Like the white part of bird poop.) If this oozing is continuous and does not stop, your lizard might have a genito-urinary tract infection. I would say take it to a knowledgeable vet OR call up a local college or university’s biology/zoology dept. and ask to see somebody who knows about reptiles.

DO NOT attempt to probe the lizard! This is a potentially injurious (to the lizard) practice best performed by experienced people on considerably larger specimens.

My favorite technique for sexing reptiles involves a toilet seat. Either that or a TV remote control.

If it is, indeed, a “mountain boomer” (aka Collared Lizard, Crotaphytus collaris), then you might be able to determine its sex by coloration. According to the Animal Diversity Web:

Incidently, here are some good pics of collared lizards, to help you determine if this is what you’ve got.

Looked at those pictures, I guess we don’t know what a Mountain Boomer is… but did find the type of lizard I have…It’s a Texas Spiney Lizard seen here And its a female by the way based on coloring… Thanks again :slight_smile: