What is the evolutionary reason for constrictors being the largest snakes

Question

I was wondering why the three large constricting snakes (Boas, Pythons, Anacondas) should be the largest snakes. Is there any hypothesis that explains why venomous snakes didn't grow to a similar size?

Answer 1

Constrictors rely on their muscles and size to suffocate their pray.  Every time the victim breathes out, it squeezes harder so that they cannot breathe in as fully.  They do not necessarily crush their pray.

But either way, size is a big factor in how easily it can kill things and the size of the things it can kill.

Venomous snakes do not need size, as their venom does all the work.

Answer 2

Generally venomous snakes follow the rule for small size but Cobras don't. They get to be an impressive size and have venom too.

Constrictors are the largest predators in areas to keep the prey animals in check. Otherwise there would be a great loss of ecosystems from overgrazing and destruction of habitat. For example:Anacondas are prevalent in South America where there are many species of Guinea-Pig-like animals, ranging in size from several pounds-up to 80-100 pounds.

Answer 3

It was a matter of filling in a gap in food chain. The large snakes were able to prey on larger animals that smaller snakes could not.

Answer 4

An important part was the availability of large prey and not too many other large predators to prevent the constrictor to evolve to fill the niche.

Their method of killing makes size and strength a big plus.  They mostly squeeze enough to prevent the prey from inhaling, once the prey exhales the snakes tighten up a bit more and the prey can not draw in enough on  the next breathe.  It is usually not that quick a killing, the victims just keep getting smaller and smaller inhalations until they finally suffocate.)

SInce the larger snakes were more successful at eating  by having access to larger prey they had better chances at breeding frequently.  Also by eating huge meals rarely they spent less time and energy hunting.