Scientific Name: Linepithema humile

How to identify Argentine ants

Argentine ants (Linepithema humile) a species which was introduced from South America and is regarded as a very serious pest which has been the target of eradication campaigns since the 1950’s. They may nest in exposed soil or concealed by plants or logs. They are 1.5-3.0 mm in size and light brown to brown in colour. They are very aggressive ants and drive out other ant species and other animals from their nesting areas. They will consume a wide range of foodstuffs - sweet foods, meat, insects, seeds and honeydew.

Where are argentine ants commonly found?

They may nest in exposed soil or concealed by plants or logs.

Why are argentine ants considered pests?

Most ant species are not considered to be pests with only a few native and introduced species causing some concern.

Some nest in decaying timber and may be suspected of actually destroying it whereas they will only infest decaying timber. Most foraging workers come from the exterior of premises but it is not particularly uncommon to find nests in roof voids, cavity walls, behind skirting boards, inside motors, inside window screens, under bath tubs, behind tiles in bathrooms and kitchens and behind taps.

In short, they like similar locations to cockroaches and as a result, control methods are very similar. Because of their nesting habits, it is common to find piles of gritty material on the floor or other horizontal surfaces or around door and window frames. On closer inspection, these piles may be found to contain dead ants which have been thrown out of the nest. No matter how often you sweep up the mess, it will re-appear as long as the ants are active.

This habit of making a little mess is not a mammoth problem but ants do become a nuisance when they are spotted walking inside pantries and getting into food containers, trailing along bench tops, window sills, skirting boards, bath tubs and invading shower recesses.

Fortunately for us, they are not generally considered to be health pests although the relatively rare Pharaoh’s ants which are often found inside hospitals are potential disease carriers as they can invade dressings of patients confined to beds and thus pose a real menace.

What is the biology and lifecycle of an argentine ant?

Like workers in many other ant species, Argentine ant workers are unable to lay reproductive eggs but can direct the development of eggs into reproductive females; the production of males appears to be controlled by the amount of food available to the larvae. Argentine ant colonies almost invariably have many reproductive queens, as many as eight for every 1,000 workers.

Management Tips For Argentine Ants

The effective control of nuisance ants depends upon a number of factors:

1. The particular species involved,

2. The location of the nest site(s) and,

3. The degree of concern they are causing the occupants.

It may be easy to control a colony with a single queen (Camponotus spp), or difficult in the case of species with multiple queens and multiple “homes” and which do not display aggression to workers from other nests (Argentine ants, Odorous house ants and Pharaoh’s ants). That is why correct identification is essential before you begin your campaign.

Ant granules were perfect for the control of some ant species to exterior areas. Most insecticide manufacturers suggest that a two-pronged approach with both baits and liquid sprays be used in order to obtain best results. These manufacturers all supply bulletins with complete instructions on how to use their products. The product labels and these bulletins should all be studied before using any of the materials.

The basic rules for the use of ant baits are:

• The basic premise is that bait should hopefully be consumed within 1 to 2 days when their palatability and moisture content are highest. The ants should die within 3 to 4 days.

• Correct identification – by knowing the species, you can choose the right bait for the job and can also help you find their feeding, trailing and nesting sites.

• Find the trails – you must place the bait where the ants are otherwise you are wasting time and bait. If the ants aren’t active at the time, you can pre-bait first with non-toxic foodstuffs. This will help you determine where the ants are feeding and what type of food they prefer.

• Choose the correct bait formulation, they may prefer sweet foods or protein based materials. Sometimes the same species will change food preferences depending upon seasons or other conditions. Therefore, you need to have a range of baits in your kit bag. If you just put a small blob of each bait in the ant trails, you will very soon find which they prefer.

Some key rules to observe when treating for nuisance ants are:

• Place the bait as close as possible to ant trails which are usually near feeding or nesting sites.

• Place adequate amounts of bait out to ensure that they will continue to feed until your next visit. By placing the bait in purpose designed “ant cafes,” you will extend the life of the bait.

• Avoid food competition by asking the client to remove available foodstuffs and liquids.

• Avoid placing gel baits near sources of heat as the gel matrix may become liquefied and moisture loss may increase. Also, avoid placing them on dry or porous surfaces which may increase water loss and make them less palatable to ants.

• Some baits lose their potency after only a few days exposure to sunlight. Make sure that you know which they are and replace them as required.

• Some granulated baits lose their potency around three months after the container has been opened. Make sure that you write on the container the date on which it was opened.

• A common piece of advice is that you mustn’t place baits on surfaces that have or will be treated with liquid or powder insecticides. Studies carried out by some researchers have indicated that this is not the case and the baits are still palatable. Some pest managers have stated, “Why waste money by applying two formulations?” and that is probably a good rule to live by. You may be able to control the ant problem without the use of insecticidal sprays and dusts but, all manufacturers recommend that bait applications are supplemented by the use of such formulations when treating free standing buildings. These insecticidal barriers will serve to prevent future ant activity to the interior.

The basic rules for the use of residual insecticide sprays are:

• Non-repellent formulations are considered superior to repellent formulations e.g. synthetic pyrethroids, as the ants will track through the non-repellent insecticide unknowingly. Examples of non-repellent actives and formulations are Bendiocarb (Ficam), Fipronil (Termidor), Indoxacarb (Arilon), Chlorfenapyr (Phantom).

• The sprays should be applied as a barrier to the base of foundation walls, fence lines and garden beds.

• Re-application of the sprays may be necessary after rain.

• Insecticidal dusts should be applied to roof voids where practical.