Red-sided Garter Snakes
Naturally wanting to look their best, Garter snakes go on a diet in the run-up to mating. For 2 weeks they go into brumation - and don't eat anything to clear their stomachs. Female garter snakes are then able to store the male's sperm for years before fertilization.
Red-sided Garter Snakes like to have a little get together - in groups of up to 25,000 or so, in order to mate. Sometimes there are 100 males attempting to mate with a female at any one time. With that many snakes things can get a bit risky, and on occasion some of the females get crushed to death - not even that stops the males, though.