The first time I visited the conservatory at Kirstenbosch (2002?), they were dealing with a terrible infestation of ants. The most visible damage was to succulents with the softer sorts of leaves--great hunks had been eaten from them. I don't know if there was any damage underground, however. Kirstenbosch keeps the bulk if its bulb collection in a separate, non-public greenhouse that may have had better controls. My own anti-ant experience has been limited to dealing with nests in pots or in the root systems of in-ground plants. They are good at excavating massive quantities of soil from around the roots, sometimes leading to dessication or death. Or they just pile the dirt on top of the plant, suffocating it. As an aside, in my previous garden I had a sand bed that was wonderful for growing some of the fussier alpines. Ants were never a problem, but burrowing wasps loved it. There were at least three different kinds that excavated long tunnels, often under plants. Fill then in, they come right back. Losses were minor, however, and they were fun to watch. --Roy NW of Boston