The Pest Advice

In my last post ‘Stop Ants Pestering You This Summer’ I described how to get rid of ants and how to keep them away. The method described will keep ants out of your home for all the pest species of ant found in New Zealand. However, and this is where it gets complicated, different species of ant are more or less susceptible to this standard treatment and some may be difficult to eradicate. A new invader, Argentine Ants, pose particular difficulties.
I will try and describe the habits of the three major pest ant species found in New Zealand; Argentine Ants, Darwin Ants and White Footed Ants, with advice on the additional control methods for each. I will start today with Argentine Ants as they are the most difficult to eradicate.
Argentine ants are very aggressive insects. Although they are not poisonous they do bite people and they are regarded as a major threat to the biodiversity of New Zealand as they are capable of eliminating other types of ant colonies and also destroying and eating other insect species and earthworms. Unlike the nests of most other ant species, Argentine Ant colonies co-operate with each other and combine over the winter into ‘super colonies’.
Argentine Ants are a common household pest and are becoming more common. They often enter structures in search of food or water (particularly during dry or hot weather), or to escape flooded nests during periods of heavy rainfall. Argentine ant nests have many reproductive queens, up to 8 per 1,000 workers. Eliminating a single queen does not stop the colony’s ability to breed. When they invade a building, it is common to see two or three queens foraging along with the workers. This habit also makes Argentine ants easily spread by the movement of items such as plant pots, boxes, vehicles etc. on which ants have been foraging. It requires as few as one queen and 20 workers to set up a new nest.

Argentine ants are generalist feeders and depending on the diet required by the colony, they will take carbohydrate, protein and sometimes fat. Kiwicare’s NO Ants Gel Bait is generally better suited to this ant species than liquid bait as it contains a large amount of carbohydrate, a good dollop of protein and small amount of fat. Argentine ants tend to forage carbohydrates all year long, but also target protein in the spring and occasionally fats and oil during the year. They tend to feed protein foods to the larvae and Queens in the nest and so protein baits are more effective for control of whole colony.

How To identify Argentine Ants?

The best way to tell Argentine ants from other ants is by their colour, trails and lack of smell when squashed. The wingless worker ant (most commonly seen) is light to dark honey brown and 2-3mm long (most other common household ants in NZ are black). Argentine ants are highly active in searching for food. Their trails are often five or more ants wide and can travel up trees and buildings. Most other species of ants in NZ don’t tend to climb trees (White Footed Ant being an exception), and would not have such strong trails unless they were moving a nest (in which case you would see ants carrying their eggs). Argentine ants look very similar to another pest species called Darwin Ant. However, if you squash an Argentine ant there is no strong formic acid smell as there is with some other ants including Darwin Ants.

If you wish to make a more formal identification of ant species check ou the excellent Landcare Research Ant Key.
Where have they been found?

Argentine Ants were first found in Auckland in 1990, more recently they have been found in Northland, Waikato, Bay of Plenty, Wellington, Nelson, Blenheim and Christchurch. Although they breed prolifically they do not swarm (fly off to establish new nests). This means they do not spread very rapidly (except when foraging queens are carried in boxes, pot plants, vehicles etc.). But when a site is infested it will have a very high number of ants and colonies. Their natural rate of invasion is a few hundred metres per year, however their main way of spreading into new areas is via transported nests and/or queens which often happens when plants or other garden materials are moved. The foraging queen ants and workers may also be transported in vehicles.
Why are they a threat to NZ?

Left unchecked Argentine Ants will become a major household and garden pest. Their huge numbers (up to six nests per square metre) mean a huge appetite and they will utilise just about any food source they can find. They have even been known to make their way into refrigerators, microwaves and screw top jars! In California they are considered to be one of the worst household pests.

Argentine Ants threaten native invertebrates as they are very aggressive and kill or drive away other insects. They climb trees and can kill baby birds in the nest. They are also active foragers and compete with other species that feed on honeydew or nectar such as insects and birds.

Argentine Ants ‘farm’ populations of aphids, scale insects and other pests that produce honeydew. The Ants protect the sap sucking insects from predators and will even move them to new plants or to new parts of the plant. This is a particularly serious threat to organic grower and growers using integrated pest management, who rely on predators to control these pests. Argentine ants have also been reported to feed directly on fruit crops and their mass numbers can damage flowers thereby reducing fruit set. They are one of the worst citrus pests in Australia, and a serious pest of viticulture, avocado and tomato crops.

Tips for controlling Argentine ants around your home.

• Contact your local authority, they may have specific requirements for control of Argentines in your area.
• Argentine Ants are difficult to deal with because of their ‘fussy’ feeding habits.
• Remove or securely store food that is favoured by ants. Clean surfaces with lemon juice, soapy water or diluted eucalyptus or tea tree oil.
• Argentine Ants may be ‘farming’ aphids and scale insects on trees and plants in your garden. Spray these plants with garden insecticide such as Super Spectrum, Carbaryl Insect Control and/or Organic Super Spraying Oil.
• Trim trees near your home to reduce ant access to your roof or window areas. Use Kiwicare two-sided tape or chalk dust around tree trunks to discourage ants (especially where birds are nesting. NO Ants ready to use trigger spray. It will be necessary to reapply barrier after rain fall (if outside) or every week (if exposed to direct sunlight). Thoroughly spray/paint all entry points into the home.
• Reduce moisture sources (e.g.: leaking taps, irrigation) as Argentine ants prefer moist conditions. Keep your roof gap and sub-floor dry and well ventilated to discourage ants from nesting there.
• Where ant trails enter your house spray with a permethrin based spray such as Kiwicare’s
• In winter you may be able to follow the ant trails back to the colony. If you can find this colony you may be able to kill it with Lawngard Prills or NO Ants Spray. But be careful not to encourage the colony to ‘bud’ i.e. move to a new nest site or sites. Contact your local authority or email Kiwcare for more advice.
• DO NOT try and spray generally for ants, as this may encourage new nests to ‘bud off’ from the main colony and could worsen the situation.