Ants: mostly fine — but watch who they're farming

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Ants march through every garden, and on their own they're not much of a problem for your plants. But there's a catch worth understanding, because ants keep some very bad company.

What do they actually do?

As they tunnel, ants aerate the mix, clean up dead insects and fallen scraps, and even help spread some seeds. By themselves, they sit somewhere between neutral and helpful.

What's the catch? (The important bit)

Ants farm sap-suckers. They herd and protect aphids, scale and mealybugs because they "milk" them for sugary honeydew — and they'll actively drive off the ladybirds and lacewings that would otherwise eat those pests. So a trail of ants running up a plant is often the first sign you've got a sap-sucker problem you haven't spotted yet. The ants aren't the pest — they're the tip-off, and the bodyguards.

What should I do?

Follow the trail. If it leads to aphids, scale or mealybugs, deal with those (a firm hose blast, a soap spray, and let the good guys back in). A sticky band around a pot leg stops ants reaching the plant in the first place. You rarely need to target the ants themselves.

Not sure whether the bug you've spotted is friend or foe? Our Garden Trouble Calendar shows the pests and diseases that are actually active in your area right now — everything else is usually one of the good guys.

Image: patrickkavanagh, CC BY 2.0, via Wikimedia Commons.