Zap Trap

Within a 40 ft wide radius of you, you may place a 5 ft by 5 ft square of zapping. For the next minute (it disappears after a minute), if a creature steps into it, they must succeed on a Strength saving throw with a DC of 15 or take 3d8 damage. 

Caltrop storm

If Zap Trap is cast upon caltrops, it will replace the natural damage of the caltrops with another roll of its own base damage.