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Life Cycle & Description

Description of Black Ants
(Lasius niger)


Temperate species living in soil or in association with dwellings. Form nests in gardens, under paving stones, in foundations or occasionally within buildings. One queen per nest. Workers very active foraging on wide range of foods including sweet substances, seeds, insects and aphid secretions (honey dew). Nests may survive for many years but young queens leaving the nest as "flying ants" start new ones each year.

Egg – larva – pupa – adult.
Eggs – laid by queen.
Larvae – legless grubs fed by workers, full grown in about 3 weeks.
Pupae – known (incorrectly) as "ants eggs", develop in 2 weeks, guarded by workers .
Adults – workers dark brown/black, 3–5 mm long. Queens winged at first, 12mm, live for several years.

Foraging workers a nuisance but not normally a health risk. They guard aphids that damage garden plants. Sexual forms, "flying ants"’, may emerge in large numbers close to or inside houses.

Only necessary where ants become serious nuisance within building. Proof entry points with sealants. Residual sprays, dusts or aerosols (some cleared for use by general public) may be used to kill or deter entry of ants. Bendiocarb particularly effective. Slow acting poison bait (sodium tetraborate) also available.

Distribution and Habitat

Commonly found in many parts of the world, and throughout Northern and Western Europe. Occurs with great frequency throughout the UK and frequently close to and in association with human dwellings. The species has a well-defined social structure, and catholic tastes. It is usually the sexually infertile females, the workers, which are seen away from the nest. The species is seldom more than a nuisance in buildings.


The formation of a new social colony of black ants starts with a mated winged female ant digging into the earth to produce a small cell. She lays a variable and eventually large number of white eggs that hatch after three to four weeks into white legless grubs. The female feeds them on nourishing secretions from her salivary glands. After about three weeks the larvae are mature and pupate within the cell. It usually takes less than two weeks for the adult ants to emerge from the pupae and this first generation will be entirely composed of workers. Once this occurs, these ants can now tend both the queen and subsequent larvae by bringing a range of food materials into the nest. They will collect nectar and seeds from flowers, small dead insects and the sugary secretions produced by green fly and black fly during the ants' "farming" activities. The worker ants also extend and enlarge the nest, cleaning out much of the excreta and inedible rubbish. They actively protect the queen, larvae, pupae and eggs, moving them to safety if need be.

Sometime in the late summer winged and sexually mature males (similar size to workers) and large females will be produced from the nest and will emerge in large numbers over a short time period. This "swarming’' often occurs from many nests at the same time and frequently in the afternoons. The winged ants fly away, mating on the wing, and eventually settling exhausted. The males usually die quickly and only a small proportion of the mated females will survive to found new colonies. Normally only one female will found each colony but sometimes new colonies are formed in close proximity. If they join up, one of the females will assume dominance and kill the others.

Ants will nest in a whole variety of suitable sites and these are generally of no significance to humans. However, sandy soil in general and the sand used to form the base of paved garden paths in the foundations of houses attracts local ants and nests may be formed. Little trouble is caused unless the foraging worker ants invade buildings. This is likely if the nest has been constructed beneath the floor of the house because ants are adept at finding even the smallest cracks in the structure; other ants are then "led" into the building.


Black ants have a wide spectrum of acceptable foods and they are particularly attracted to sweet substances. One successful foraging worker is able to communicate the information to her co-workers, with the inevitable result of vast numbers of worker ants invading and incidentally contaminating suitable human foods. Although not inherently "dirty" insects, they must sometimes walk across unsavoury and unclean areas during their foraging exercises and this leads to ants invading houses being considered unacceptable. Unlike the tropical ants which infest hospitals and other institutions (please see the reference to Pharaoh’s ant), the black ant is not known to transmit serious disease organisms.


Control measures are generally only required where ants are penetrating, or on occasion living in, building structures. In cases of penetration the first approach should be to seal obvious faults in the structure using mortar/cement or mastic, as appropriate (see illustration). It is best to support such proofing measures by the application of a residual insecticide band to likely access areas.
Dust (1%) or spray formulations of bendiocarb are particularly effective for professional use against garden ants and can provide several weeks' protection in fair weather. The dust formulation is particularly useful if blown into any voids harbouring colonies. It may be possible to treat the area of outdoor nests with insecticides, if this is deemed necessary. This may simply encourage any survivors of the colony to move to another nest site.

Bait formulations for use against garden ants are usually available as products for professionals and amateurs and may be of limited effectiveness. On the occasions when some "delayed action" active ingredient is transported to the nest a decline in nest growth will result.

Finally, many "household" insecticide aerosols are cleared for use against crawling insects. Their use is likely to offer only short-term relief in view of the relatively low dose of active ingredient likely to be applied.


Description of
Pharaoh's Ant
(Monomorium pharaonis)

Tropical species found only in heated buildings in UK. Small, mobile and active at all times of day. Form large, apparently unstructured, nests in cavities and heating ducts. Many queens per nest. Workers seen in distinct trails between nest and food sources. Forage on wide range of foods and need access to water. Infestations spread by "budding", groups of workers and sometimes queens leaving the main nest with brood to form satellite colonies.

Egg – larva – pupa – adult.
Eggs – laid by queens within nest, hatch in about 1–2 weeks.
Larvae – legless grubs fed by young workers in nest, full grown in about 3–4 weeks
Pupae – develop in about 2 weeks guarded by workers in nest.
Adults – workers wingless, 2mm long, yellowish, live about 10–12 weeks. Queens winged, 4-5mm, normally stay in nest, live up to 10 months. Minimum development temperature 18
°C, optimum 30°C.

May carry disease organisms. Contamination of food and sterile materials.
Can penetrate packaging due to small size. Ability to travel through ducting and building structure means infestations can become very widespread. Satellite nests may be transported from one building to another.

Only necessary where ants become serious nuisance within building. Proof entry points with sealants. Residual sprays, dusts or aerosols (some cleared for use by general public) may be used to kill or deter entry of ants. Bendiocarb particularly effective. Slow acting poison bait (sodium tetraborate) also available.

Distribution and Habitat

Successful control only by baiting techniques, not by residual treatments.
Hydramethylnon, a slow acting poison, and S-methoprene, a juvenile hormone that disrupts larval development, are available as ready-to-use baits.


Unlike the common black ant where one queen lays all the eggs, Pharaoh's ant colonies contain several queens, all of which may lay eggs. Queens have wings when they first emerge but these are soon lost. Winged males will appear from time to time and mate with new queens. And so the colony will continue unabated and probably increase in size, with old queens being replaced by new ones, provided that the necessary physical and food requirements are maintained. The ultimate nest size appears to be dependent more on physical space availability rather than an absolute maximum number, and nests of up to 50,000 workers and 100,000 young stages have been found.

The Pharaoh's ant, in common with all species of the order Hymenoptera (bees, wasps and ants), follows a complete metamorphosis (life cycle). Development times vary mainly according to temperature. The eggs laid by the queen hatch after one to two weeks into tiny larvae, or grubs. These are fed and tended by the sterile female workers and take about two to four weeks and several skin changes (ecdyses) to reach the pupal stage. This stage lasts two to four weeks and is protected by the workers.

Workers will move pupae and young larvae away if danger threatens the nest. This may also happen deliberately to start off new colonies, a process known as budding by which ants gradually spread throughout buildings or complexes.

Sometimes new queens will accompany these migrating groups. This is not essential since the workers can produce new queens, and males, from the developing young.

The tropical origins of the ant are indicated by its requirement of a minimum breeding temperature of around 18
 °C, with an optimum of around 30 °C. They are usually associated with central heating systems, ovens and sometimes heat exchange units (calorifiers) in institutions such as hospitals, prisons and increasingly in high-rise apartment dwellings, when these are heated throughout the year. It is the worker Pharaoh's ant that is most commonly encountered. These sterile females are the foraging caste and will search for suitable food sites many metres from their nest location. They communicate information regarding suitable food sites to other workers using chemical (pheromone) trails and it is common to see long narrow trails of worker ants moving to and from the food source. The ants also search out liquid water for drinking and this often brings them into contact with unsavoury areas such as drains and waste-food collection bins.


It is clear that the foraging activity of the worker ants, combined with their small size and ability to chew through materials, can be responsible for the transmission of disease bringing organisms from dirty and unsavoury situations to clean food, and perhaps more importantly, into otherwise sterile hospital supplies. They have quite a wide taste in food materials but are known to be particularly attracted to suppurating wounds of patients in hospitals causing intense irritation and the ever-present prospect of the transmission of pathogenic bacteria.

The importance of Pharaoh's ant is also related to the difficulty of eradication. The worker ants ability to "bud-off" new colonies where suitable conditions exist, or if the original colony is subjected to unusual stress, frequently results in many smaller colonies existing as satellites. A building may be infested with Pharaoh's ants that will not necessarily be located at one nest site. Additionally, the ants are spread quite easily from building to building by the temporary formation of very small nests in movable items such as clothing, bedding and even in linen baskets. The cost of survey and control for a Pharaoh's ant infestation can be considerably greater than anticipated due to the extent and complexity of the nest-formation characteristics.


This pest can be particularly difficult to eradicate and has been present in some premises for many years, despite continued efforts to control it.

Residual sprays and dusts are usually ineffective in eradicating Pharaoh’s ants. Their use may bring temporary relief in small areas but apparent success is usually illusory. The difficulty of accessing nests means that such treatments rely on killing workers in an attempt to starve the nests (containing brood, nurse workers and queens) of their food supply. This rarely works because insufficient numbers of workers are killed and nests also contain reserves of food. Furthermore, the presence of insecticides within range of a nest may induce migration away from the treated area, encouraging the spread of infestation.

The strong trailing habit of the worker ants has encouraged the use of baiting techniques that currently offer the most effective method of control.

Baits may contain either a slow acting stomach poison or an insect growth regulator.

Baiting techniques rely on the continued attractiveness of the bait base over a period of time, long enough to bring about control. It has been noted that Pharaoh’s ants may exhibit a phenomenon known as "bait tiredness" whereby workers will cease to be attracted to a particular bait formulation if this is used for a long period.

Whichever product is used a thorough treatment must be carried out to ensure that all nests are treated. It is important that a detailed survey of the premises is undertaken to determine the extent and degree of infestation. It is also important to ensure that no residual insecticide treatments have been carried out prior to baiting, which might reduce the foraging activity of worker ants.

Except in very heavy infestations of Pharaoh's ants, visual survey does not easily detail the extent and degree of an infestation. It is usual to carry out a pre-treatment survey by placing small amounts of attractive bait throughout the entire site, including adjacent properties. The baits are then examined after 24 hours for ant presence or signs of being eaten by ants.

Any attractive bait base may be used including plain raw liver.
Mixtures containing combinations of liver (fresh or powdered), peanut butter, sponge cake and honey presented in short lengths of large diameter drinking straws or tubing are more convenient and less messy. Ready-to-use survey/monitoring bait stations are also available.

Baits may be applied at a density of one bait per 10–50m2 in areas likely to attract workers. It is important to ensure an even distribution of baits so that no infested areas are missed.

Slow acting poisons
Slow acting poisons formulated in an attractive bait base are collected by worker ants and transported back to the nest where they are fed to larvae and adults. The delayed toxicity allows time for the workers to transport a sufficient quantity of bait to the nest before they themselves succumb. With this method all stages, including workers, should be killed.

Ready-to-use bait stations containing hydramethylnon formulated specifically for Pharaoh’s ant control are applied at a recommended average rate of one bait per 10m2.

Juvenile hormone baits containing S-methoprene
S-methoprene is a juvenile hormone analogue, a substance that mimics a naturally occurring insect hormone. Mixed with an attractant bait base it is collected by workers and fed to the larvae and queens, This has the effect of (i) sterilising queens to prevent further production of viable eggs, and (ii) preventing developing larvae from reaching the adult stage. The workers are not directly affected but as they die at the end of their natural life span (10–12 weeks) they are not replaced by emerging adults and the colony gradually declines.

Currently S-methoprene is available, formulated with an attractant bait base, as ready-to-use bait stations. These are applied at a recommended average rate of one or two baits per 5m2, -depending on the level of infestation. Control should be achieved in 12–14 weeks if used correctly.

S-methoprene treatments do not have an immediate dramatic effect but in most cases it is better to rely on bait alone, used as directed. In some sensitive situations (e.g. hospital wards or operating theatres) where ant worker numbers must be reduced quickly, a localised treatment could be carried out using a residual insecticide at 10–14 days after the completion of the baiting treatment. Most pyrethroid or carbamate/OP active ingredients will kill Pharaoh's ants. Bendiocarb is particularly effective in either wettable powder or dust formulation. Residual insecticides should not be used immediately before or during baiting treatments because if workers are killed (too quickly) the bait may not be transported back to the nest. Disruption of the colony structure may also result in the nest being "moved" to a new location.


If your having issues with Ants or any other pest related problem within your commercial or domestic property then please feel free to contact us on 01282 777549 or email us at for an immediate response.

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