“Pit of snakes” is probably the most culturally loaded entry on this list, thanks in large part to adventure movies and old exaggerated travel stories that turned it into shorthand for a nightmare scenario. The real biology behind it is far less sinister, and much more about geography than menace.
Low-lying depressions, sink holes, rocky pits, old wells, make convenient natural shelters, offering shade, stable temperatures, and protection from predators and weather. Snakes seeking exactly that kind of shelter can end up sharing a pit the same way they’d share a den or burrow, drawn by the location’s practical value, not by any coordinated plan. In areas with dense snake populations and limited good shelter, a genuinely large gathering in a single depression isn’t just movie fiction; it does happen, particularly around denning season.
The dramatic reputation says more about how humans have long reacted to snakes than about anything unusual in snake behavior itself.
Example: “Local legend called it a pit of snakes, though it turned out to be a modest den of maybe a dozen.”
Related: Collective Nouns for Reptiles · What Is a Group of Snakes Called?