Q Do ants cause damage to plants?

A Ants seldom feed directly on plants, but they can sometimes damage plants in other ways. When ant colonies build their nests under plants it disturbs the roots and deprives the plants of water. They can also bury plants by depositing soil on them when excavating nests – which can be very damaging in rockeries and flower pots. This is usually done by black ants (Lasius niger), though the common red ant (Myrmica ruginodis) may also be responsible. When ants are not directly underneath plants, they can help by loosening the soil, thus improving soil structure and drainage.

In lawns, ant hills are a nuisance as they interfere with mowing. Mound ants or yellow meadow ants (Lasius flavus) are the worst offenders. Their mounds are, however, usually flattened by passing feet and mowers. These ants prefer lawn edges where there is less disturbance.

Ants feed off the honeydew excreted by various insects such as mealybugs, scale insects and aphids. Ants protect these pests by fending off their predators. However, some aphids won't produce honeydew for the ants and in that situation the ants may eat them!

Some ants, including yellow meadow ants, also farm aphids on the roots of plants.

Caption: Ants farm aphids so they can eat the honeydew they excrete

Q Why are ants often seen on plant stems?

A If a plant is infested with insects that excrete honeydew, ants can often be seen collecting it and protecting the insects that produce this sugary substance. By eating the honeydew, ants actually help plants. Honeydew, while not damaging in itself, supports the growth of sooty moulds. These moulds have dark spores which turn the leaves black. The shading of the leaves by these spores reduces photosynthesis.

Caption: Sooty mould grows on the honeydew which ants eat

Q What else do ants feed on besides honeydew?

A Ants feed on sugary substances such as nectar, on small insects and even on other ants. Some species of ant also collect oily seeds from plants like buddleia, cyclamen, cabbage, heather, meconopsis, primula, radish, rhododendron and viola. Only one British species of ant eats seeds, and this isn’t found in gardens, but ants do eat seedcoats or other nutritious attachments that have evolved to attract them.

Seed collection by ants can be troublesome, especially in warm weather in late spring and summer when ants are most active. If you get poor germination at this time, ants could be a suspect – though this is usually only significant in greenhouses. Ants can also be responsible for spreading weed seeds. In a warm greenhouse, tiny pharaoh ants (Monomorium pharoaonis) and Argentine ants (Iridomyrmex humilis) may appear. These imported species have been spread as passengers on plant material. They feed on small insects such as wireworms, caterpillars and mites, and they help to destroy many pests.

Wood ants are so important in destroying forest pests that in some countries, such as Germany, they are protected by law.

Ants can attack helpful insects, but on balance, their hunting is useful.

Q Which ants sting you?

A Ants found in the garden don’t usually sting or bite. If disturbed, ants will rush out and 'attack'. They will attempt to bite but their jaws are too weak to do any damage. Red ants are able to sting.

Q How do you control ants in the house?

A Black ants are the only species likely to venture indoors. They don't live in houses but are just foraging for food. Blocking entrances and hiding sugary substances will often prevent an invasion. You can kill existing ants with a bait station.  The small openings in ant stations mean that pets won’t be able to reach the bait

Q What kinds of ant do I have in my garden?

A There are many types of ants in the UK and most are active between April and October. These are the most common.

Black ants (Lasius niger) As well as gardens, these tend to enter houses, too. They will nest anywhere and are harmless. They have a taste for sugary substances and are active foragers, so if you place your bait station or powder near their foraging path, they will find it quickly.

Red ants (Myrmica rubra) These are deep red rather than orange or yellow, and can give you a painful sting. They tend to live in small nests. Like the black ants, they have a taste for sugar and are active foragers, but are far more aggressive. Take the time to discover their foraging pathways to find the best place for the bait station.

Yellow meadow ants (Lasius flavus) These are very small ants and are rarely seen on the surface unless you disturb the nest. They forage below the soil, feeding on small insects, so are more difficult to tempt with bait. They are completely harmless, but do leave small earth mounds on lawns and flower beds.

Q Why are ants called social insects?

A Ants are related to bees and wasps and live in colonies. Each colony makes a nest which contains many worker ants – wingless females that cannot lay eggs. There will be one or more larger, egg-laying queen ant which has been fertilised by winged males. The nest is their base for breeding and where their foraging expeditions start from.

Q Can you tell me more about the ant colony?

A Colonies are founded by queen ants after their mating flights in late summer, typically in August. Both mound and black garden ants produce huge swarms of flying ants; these are the queens and males, which mate in flight. Many nests produce swarms of mating ants at the same time, which is why there sometimes seem to be plagues of flying ants. The swarms are a nuisance for a while, but they provide food for many birds and soon die down.

The males die after mating. The queen lands at a suitable site, such as the edge of a lawn or the base of a wall, bites off her wings to facilitate burrowing, then excavates a nesting hole. She looks after the young larvae until they develop into wingless workers that carry on building the nest and rearing more ants.

Ants make nests in varied locations. The nest contains many tunnels, full of worker ants. In winter the nest becomes dormant and the workers stay inside. When spring arrives they go out to search for food. Some species just forage randomly, but others lay scent trails to the food supply for other ants to follow.

Pharaoh ants don't mate in flight. A queen leaves to form a new nest, with workers carrying larvae and pupae.

Q How long does an ant nest survive?  

A Ant nests can exist for many years, with the worker ants excavating the nest, feeding the queen and larvae, and fighting off predators. Each summer new winged forms are produced.

Q How should I get rid of ants?

A Usually you don't need to bother. Just keep down the aphids, scale insects and mealybugs with suitable controls. Where plants are loosened, firm them back into the soil and water well. Good watering tends to discourage ants, as they prefer dry conditions.

If plants are seriously damaged, or if ants are a problem inside the house, it’s better to follow the ants back to their nest rather than where you see them. The nest can then be treated directly, and this saves having to use insecticides in the house or on plants.

Q How do I get rid of ants in the lawn?

A Ants can be a pain in the lawn as they make ant hills. These may not be big but they cause patches of earth which allow weeds to get into the turf. Some people use boiling water to kill these ants but this isn't a good idea as it results in scorched patches of turf which again are vulnerable to being colonised by weeds. It's better to water the ant hill regularly with cold water as this won't kill the turf but will disturb the ants and encourage them to move on.

Caption: Ant hills cause patches of earth that weeds can colonise

Q How can I get rid of ant nests and ant hills?

A Ant nests (hills) are best broken up with a fork and treated with an insecticide such as a drench or dust containing bendiocarb or deltamethrin.

Q What can organic gardeners use to solve ant problems?

A On uncultivated land, boiling water can be poured into nests. In cultivated areas, cold water can be used instead. This won't kill the ants but it will create damp conditions which they don't like and will encourage them to move elsewhere. This is a solution if the nest is accessible, but if it's buried beneath a paving slab, the water may not reach the nest.

If ants are crawling around paving then a control containing diatomaceous earth will cause them to dehydrate and die. In our test, Oa2ki Organic insect powder, which contains diatomaceous earth, killed almost 90% of black ants over the 20-day trial period. However, it was less successful on yellow meadow ants where only 50% were killed. It works best in dry conditions

There is also a nematode-based biological control sold online and by mail order as Nemasys No Ants. This doesn't kill ants but aims to encourage them to move elsewhere. However, when we asked ant-plagued Which? Gardening members to try it, most were dissatisfied with how well it worked as even if the ants did relocate, they were still a problem. Also, this treatment isn't suitable for controlling ants nesting beneath hard surfaces such as paving. Stockists include Green Gardener: 01493 750061 greengardener.co.uk

Q Are ant bait stations effective?

A Yes, but you must keep replacing the baits as long as the ants visit. Baits work best for black ants, as other species don't take them so enthusiastically. They’re worth trying where you can’t find the nest, or when the nest is inaccessible, such as when it's in a wall.  The small openings in the bait station mean that garden animals, such as hedgehogs, and pets won’t be able to reach the bait.

Q Would it be worth treating every ant nest in the garden?

A No. If every ant nest in the garden is treated, winged female ants from neighbouring gardens seeking new nest sites in the summer are more likely to survive. This is because worker ants predate on new queens, thus keeping a natural balance in the population.