I don't really know d&d well, but I just looked up the spell and I think it says you can transform "any number of willing creatures". So the DM could make an argument about whether insects had the intelligence to even qualify as being able to be "willing" for that.
On the other hand, I am a big fan of Operation Dumbo Drop Multistrike
Depends on the edition. If Epic Magic is in play, 9th level spells are just the beginning. However, it gets stupidly easy to kill yourself by casting something that you really shouldn't have tried to cast.