It's a pretty sweet idea, though it feels lacking in terms of the code's finer details.
I'd like to see you reduce the time for the insects to de-spawn, because having so many objects on screen made the firing rate slow down to the point of where the spiders were basically useless.
I had 8 spiders who went from firing a solid line, to chugging and struggling to fire 2 each second. All the while, the insects are not slowing down, they're all conglomerating at the bottom of the tree, more and more are spawning while there's dozens of dead ones littered about, the insects haven't gotten any slower, but I'm struggling now to keep going.
Because of the way that the insects spawn and de-spawn, it dooms you to failure, no matter what.