Scientific names Various, mainly Lasius, Myrmica and Formica species
Plants affected Ant nests frequently occur in lawns, flower pots, compost bins and among the roots of plants
Main symptoms Small heaps of fine soil on the surface above the nest; presence of ants
Most active April-October
What are ants?
Ants are eusocial insects related to bees and wasps (Hymenoptera). They live in nests that contain many hundreds and sometimes thousands of ants. Most are wingless sterile females, known as workers, but there will also be fertile females, known as queen ants, and males. More than 30 species of ant are found in Britain, a few of these can occur in gardens, including the familiar black garden ant, Lasius niger.
Ants can cause concern but they are at worst a nuisance rather than destructive insects. Ants can be an important part of the biodiversity of a healthy garden. The eusocial nest structure can be complex with different casts and ages of worker ants. They often have mutualistic associations with sap sucking insects such as aphids.
- Ants feed mainly on other invertebrates, including other ants
- They also collect the sweet liquid known as honeydew, which is excreted by aphids and some other sap-feeding insects
- Ants can protect aphids from attack by ladybirds and other predators in order to secure their supply of honeydew. Increased numbers of aphids may result in more damage to plants
- Ants do little direct damage to plants, except by disturbing soil around plant roots and depositing it on the surface during their nest building activities. This can be a nuisance on lawns and where low-growing plants are being buried by excavated soil. They may also disturb plant roots in pots and containers. This disturbance can also mean that plants are more prone to wilting especially when dry at the roots.
- Sometimes ants will nest in a compost heap or bin. They will not be causing any damage in this situation
- Some ants (mostly Myrmica species - commonly known as red ants) can sting, but for most people this is no more than a minor irritation
When choosing control options you can minimise harm to non-target animals by starting with the methods in the non-pesticide control section. If this is not sufficient to reduce the damage to acceptable levels then you may choose to use pesticides. Within this group shorter persistence pesticides (that are usually certified organic) are likely to be less damaging to non-target wildlife than those with longer persistence.
- Ants should be tolerated in gardens wherever possible, they do not cause direct damage to garden plants and are an important part of the biodiversity gardens can support
- Unless nests are particularly troublesome, ants are best left alone. If a colony is destroyed it is likely that its place will be taken by in-coming queen ants, which take over the territory and establish even more new nests
- Disperse ant heaps on lawns by brushing the excavated soil on a dry day before the lawn is mown, otherwise the soil will get smeared on the lawn surface by the mower
- If the lawn has an uneven surface due to years of ant activity, peel back the turf in the raised areas, remove excess soil and relay the turf. This is easier to do in the winter when ants are less active
- A pathogenic nematode, Steinernema feltiae, is available from some suppliers of biological controls for treating ant nests in lawns and flower beds. The microscopic, worm-like nematodes are watered into the soil in places where ants are bringing soil up onto the surface
Pesticide controlThe RHS believes that avoiding pests, diseases and weeds by good practice in cultivation methods, cultivar selection, garden hygiene and encouraging or introducing natural enemies, should be the first line of control. If chemical controls are used, they should be used only in a minimal and highly targeted manner.
- Controlling ants with pesticides is often impractical and ineffective
- Many proprietary ant powders, baits, sprays and aerosols are available for controlling ants in and near buildings, these are not suitable for general garden use or application on plants
- To make a real impression on ant numbers it would be necessary to destroy the nests rather than just the foraging ants. That is difficult to achieve as ant nests occupy a much larger volume of soil than the surface excavations might suggest
- In most situations try to tolerate the presence of ants
Biological control suppliers (downloads pdf document)
Ant nests contain one or more fertile female queen ants, which lay eggs in brood chambers within the nest. Most of the other ants in a nest are smaller wingless sterile females, which are known as worker ants. Their role is to maintain, guard and enlarge the nest, feed the larvae and gather food for the colony.
- The white maggot-like larvae are fed on a liquid diet secreted by the worker ants
- When fully fed, the larvae turn into pupae
- Some species of ants pupate inside spindle-shaped whitish-brown silk cocoons. These cocoons are often referred to as 'ant eggs'. The real eggs are very small and not easily seen with the naked eye
- At certain times of year, ant nests produce winged ants. These are young queens and male ants, which often emerge en masse (often labelled 'flying ant day', the mating masses can be picked up by weather radar) from nests during humid weather in the summer. These fly up and mate, after which the males die and the young queens try to find suitable places where they can establish new nests
- Once mated, the queen ant no longer needs wings, so they are bitten off
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