I read with interest Wintermist's ant problems. I recently found a potted fern so badly infested with ants the soil was virtually ruined.

I've heard it said that a sudden ant invasion is a sign of rain in garden-lore?

Happily though, there are some insects beneficial to the garden:

Beneficial Insects -
Beneficial insects in the garden help create a balanced garden and include:
ladybirds, lacewings and hoverflies which help keep down aphids, scale insects, red spider mites and caterpillars;

and of course bees by pollinating flowers.

Plants which attract insects include: marigold, dill, sweet alice, coriander, echinacea and cosmos and tree dahlia's.