I became interested in saffron several years ago, and by some 'coincidence', came across a garden center close-out, '90% off saffron corms'. Of course I bought the entire gross. Here in zone 6b, they seem to do well, even though I've been neglectful in not dividing them. My second-hand experience with moles, voles, etc. has been that they are burrowing primarily for grubs and earthworms, and the corms are just a tasty snack. If you use an insecticide for the grubs, then apply a strong tea of hot pepper, this should discourage burrowing vermin. (I would never kill earthworms....) The drawback of hot pepper tea is that it has to be applied every couple of days to be effective. On a side note, if you're battling squirrels or grazing animals, a few drops of a week-old solution of rotted egg (1 raw egg mixed in 3 liters water), also applied every 3 days, is highly effective and cheap! The solution doesn't off-gas, and is useable for at least 2 months. It has kept the squirrels out of my pots, and a few thin strips of paper dipped in this and hung on tree branches will send deer running. Applied in moderation, it shouldn't be detectable to humans.