During the Verm event (just before Hammerlock dlc came out) we found that it was quite tough to get Varkids to evolve with only two players, but a lot easier with three. Not sure if that's still the case in normal play though.
Verm is not that tough to spawn (unless you're trying to do it solo). He's also not that hard to beat since you can hide in the shed to avoid him. It's definitely worth attempting, he's hilariously huge and nowhere near as frustrating to fight as Terramorphous. Hope you're luckier than I've been with the drops though..
Tempted to do Verm this weekend but a) appears to be a complete pain in the arse to spawn and b) Terra took us forever.