We're Gonna Need More Fireballs

Tower defense against bugs

We're Gonna Need More Fireballs is a PC game about defending towers from bugs pouring through tunnels. You build towers and keep casting spells to burn the approaching swarm.

Fire, rot, and hungry trees

Fire is the main answer, but it isn't the only one: you can rot the bugs or feed them to hungry trees. The threat is described as a million bugs coming down tunnels the size of a city, and the game’s instruction is simple: don't stop casting.