Are they earth size bugs, or are they giant bugs, because if they are earth size bugs then I don't really think they could decimate the populations of the animals they hunt.
Decent game nicely done. Just needs more lvls and a few different upgrades or even helper chickens that fire at the ufos as well. Add more variations of enemies Like a final boss Ufo that can abduct multiple cows at a time and to destroy the ufo the individual tractor beam generators need to be destroyed first then the ufo itself.
Please, could you send webplayer log for me: http://docs.unity3d.com/Manual/LogFiles.html, mb there are errors i didn't see before.