Ants
Formicidae
Ants eat almost nothing you grow. What they do is farm the aphids that do — and undermine roots with their nests, which is the real damage.
Everyone knows an ant. What matters in the garden is the behavior: a steady two-way column running up a stem to a colony of aphids, ants stroking them for honeydew and driving off the ladybird larvae. On the ground, a fine crater of excavated soil around a nest entrance, often between paving slabs or under a pot.
- A column of ants running up and down a stem to an aphid, scale or mealybug colony.
- Aphid numbers rising on a plant the ladybirds have plainly visited but not cleared.
- Fine excavated soil heaped around a nest entrance, in a lawn, a path, or under a pot.
- A plant wilting in dry weather because a nest has hollowed the soil out around its roots.
- Sticky honeydew and sooty mold below the farmed colony.
A colony of a queen and her workers, persistent in one place for years, tunnelling and moving soil constantly. Many species farm sap-sucking insects deliberately — moving them to fresh growth, defending them from predators, and in some cases overwintering their eggs. Winged queens and males fly on a warm, humid day in midsummer and start new colonies.
Warm, dry, well-drained soil, and gardens with plenty of aphids. Nests concentrate under paving, in dry banks, in pots and along wall bases. Numbers rise sharply in a dry summer.
- Deal with the aphids and the ants lose interest; the aphid is the reason they are there.
- Band the trunk of an affected tree or shrub with a grease band or sticky barrier so the ants cannot climb to the colony.
- Water a pot or a plant with a nest under it thoroughly and repeatedly; the colony will usually move rather than drown.
- Brush the excavated soil back into the lawn on a dry day and level as you go.
- Do not scatter ant powder through a border. It kills ground beetles and the ants come back.
- Keep aphid numbers down and the ant problem largely disappears.
- Water plants steadily; a well-watered soil is less attractive for nesting and a plant with a nest under it copes better.
- Fill and point gaps in paving where nests establish.
- Grease-band fruit trees in spring.
- Accept ants in the wider garden. They aerate soil, disperse seed, and take a great many pest insects themselves.
The Cottage Garden Companion — the gardener's bestiary at cottagegardencompanion.com