More often than not, when you least expect it, they are just there. You don't see them approaching, you don't hear branches cracking or leaves rustling--they are just there.
Even a harmless garter snake will make you jump back when you reach into the irrigation controller, and realize that a couple of the "wires" are moving. Maybe Mother Nature actually has a sense of humor, and this is her idea of a practical joke. Well, if so, it works every time.
Although they are weather-proof, many creatures manage to set up camp in the controllers. We've come upon ant colonies, wasp nests, mice, and of course, snakes. Deterrents include installing screening, foam insulation, no pest strips, and moth balls.
But given the cold and snowy winter conditions this year, it was probably worth the extra effort for these guys to find a way to sneak in. However, since it looks like spring has finally arrived, we'll kindly ask them to relocate for the warmer months.