The Spike Trap is often considered every Keeper's "bread and butter" trap; it is the first trap that is unlocked, and more become available for building as more mines and quarries are claimed. While the damage they deal is on the low side, they have a relatively short cooldown. Spike traps are placed on the floor, and are hidden until they are triggered the first time (by an unsuspecting enemy walking over them!). Flying enemies (like Ghosts or Dragons) will fly over these traps, and are thus unaffected.
Why would you choose this trap over another? They're cheap, and you're able to place more of these than any other trap.
Strategically, the best place to position a Spike Trap is in front of a door or trap that is blocking a patch, as well as placed several-in-a-row near an Ice Trap.
With each upgrade (up to 7), Spike Traps deal more damage.
Watch your step, Keepers!