Question on snakes being "loners"

I have a question and hopefully someone can answer it backed up w/ data.

We all know snakes should be housed separatly or so it is said. Also being said is that snakes are solitarily animals. If that is indeed the case then why do you find huge "dens" of say Rattler's or Garter's?

Not debating just wondering the difference's. Also the National Zoo here in Washington DC has some, not all, snakes housed together? And running the snake house at the Zoo is some leading herpologist ( spelling )

Seeing this just makes me go Hmmmm.....
Can anyone help the sister out :)

i was wondering that myself, just never said anything. the san diego zoo housed pythons in the same enclosure

They do this to stay warm in the winter months - communal hibernation allows them to survive conditions which, on their own they would succumb to. This occurs not only rattlers but hognose, gophers and a variety of other snakes.

The majority of boids are from warmer climates and do not need to resort to this survival tactic.

Did a bit of research on this. One bit of info from the Fresno zoo mentions that when snakes den together and "ball up" in a mass of snake bodies it effectively reduces the surface-to-mass ratio which allows for less loss of heat and moisture for the snakes. Also I know certain snakes like garter snakes mate in a mating ball (many males and a female) right as spring starts so perhaps by denning up together it gives them a fast way to get on with this first spring mating activity.