Yesterday my dad and I had a conversation about the eating habits of boa constrictors. It involved a goat and a lot of resting on the part of the snake. And it made me really want to do a post on boa constrictors.

Boa constrictors are found in Central and South America, from northern Mexico to northern Argentina. Their preferred habitat is rainforest, though they can also live quite happily in grasslands, thorn scrub and semi-deserts. Boas are not uncommon around human developments, particularly in agricultural areas (where I’m sure they can find lots of tasty goats to munch on). They like to hang out in trees, though younger boa constrictors spend more time in trees than adults.

Many people think of boa constrictors as some of the biggest snakes in the world. This is not true, as there are a number of snakes bigger than boa constrictors. They do get reasonably large, however, reaching maximum lengths of 4.3 m, with sizes between two and three meters being more common. Female boas are usually larger than males. They are brown to cream coloured, with saddle shaped bands covering their bodies. The markings darken as they approach the tail, turning into a reddish brown colour. The snakes have distinctive head markings, which I could describe, but it’s much easier for me to show you a picture, so here’s one:

The head patterns of a boa constrictor.
Image by Bjørn Christian Tørrissen, CC BY-SA 3.0, via Wikimedia Commons

Boas have two spurs on each side of their cloacas, which are left over from long ago when snakes thought having legs might be helpful. Today, these spurs are used in courtship and to grip the female during copulation, and thus are larger in males than females. Males also have a double penis, known as hemipenes. They usually only use one side of the hemipenis, though, so it’s not quite as nice as it may sound. Females give birth to live young after a five to eight month gestation period. A litter is usually 25 young, but can be as high as 64. Thankfully, the mother doesn’t invest any care in her young after birth, so she doesn’t have to look after 64 babies.

Boa constrictors use a variety of senses to navigate their environment. They flick their tongues in and out of their mouths, which brings odours into the vomeronasal organ, located at the top of their mouths. They do not have heat sensing pits like other species of  boa, but can sense heat on their lips. Boa constrictors have quite good vision, and can see ultraviolet light. They don’t have external ears, but can sense vibrations in the ground and air through their jaw bones.

As boas get older, they get heavier, and start becoming more terrestrial.
Image by Andreas Schlüter, CC BY-SA 2.5, via Wikimedia Commons

Boas don’t usually actively hunt, instead preferring to ambush prey. They consume any animal that will fit in their mouths, generally eating small mammals and birds (probably not many goats). The snakes catch the prey with their teeth, and then wrap themselves around it, using their bodies to cut off the victim’s circulation, thus killing it. Constriction seems to be something the boas can’t help — they will constrict an animal even if it is already dead. Digestion of the prey takes four to six days, and the snake doesn’t have to eat for a few months afterwards, as it possesses a very slow metabolism.

Venomous snakes are neat, because highly toxic substances are always impressive. But those that squeeze their prey to death are also pretty awesome, because what’s not to love about an animal that crushes things so hard their blood stops flowing? Still, I’ve always been a snake fan, so I’m probably biased. If there were constricting spiders, I have a feeling I wouldn’t like them nearly so much.

Cover image by Christian Mehlführer, User:Chmehl, CC BY 2.5, via Wikimedia Commons, cropped to fit