Pest Ants in New Zealand

PEST SNAPSHOT - ANTS

Class: Insecta
Order: Hymenoptera (related to wasps and bees)
Family: Formicidae
Health threat: Generally low
Bite / sting pain: Varies depending on species from no sting to severe pain
Difficulty to control: Challenging
Diet: Honeydew / insects / seeds, depending on species
Main pest season: Summer / Autumn
Indoor/Outdoor pest: Both

Ants are eusocial insects and belong to the Family Formicidae. They are related to bees and wasps, and all belong to the order Hymenoptera.
There are more than 12,000 species worldwide. New Zealand has remarkably few ant species – only around 40 species have been identified. (In Australia nearly 1,300 have been identified).
Ants are considered one of the most difficult crawling insect pests to control.

Pest Status

Although the majority of species are not considered pests, the reputation of the main pest ant species has resulted in ants being considered to be the number one global crawling insect pest.

Controlling ants is a challenge, due their sheer numbers and the nest/colony structure – to get lasting control you need to kill the nest, targeting the queen(s) as they are the colony’s egg production unit.

In the domestic situation, they are more of a nuisance, causing food spoilage and stinging/biting homeowners and pets. However, activity in and around electrical wiring is a known cause of house fires.

In commercial situations, they can be a problem in food handling establishments and certain horticultural and agricultural areas.

Perhaps their most significant impact is as environmental pests. Of the world’s top 100 invasive species, five are ants; Argentine ant, big-headed ant, crazy ant, little fire ant and red imported fire ant. These species have been transported around the world by humans and quickly invade new areas, decimating the local ecosystems.

In New Zealand, Argentine ants are a major problem, big-headed ants are present in warmer areas and there are a few spots where crazy ants have been identified.

Fortunately, fire ants are not present in New Zealand.

Health & Safety

Ants getting into food in homes and businesses is more of a nuisance and issue of contamination, as they are not known to spread disease. However, contamination is a serious issue for food management businesses, as no-one wants ants in their food!

However, a couple of ant species do deliver very painful stings, which hurt at the time and can itch for days afterwards. For some people, they can cause allergic reactions which sometimes result in anaphylactic shock which requires urgent medical intervention.

It is important to note that although ants bite (grab on to you with their jaws), it is their sting that hurts. The sting is a needle organ that is thrust out from their abdomen and injects the venom.

Green-head ants are one of the most common stinging ants in residential areas and are commonly found nesting in lawns. Originally from Australia, they are found in an increasing number of areas on the North Island. Although their bites are considered ‘only’ moderately painful, their sting area can itch for days afterwards.

Types of ants

There are only around 40 species of ants in New Zealand, so with a bit of practice it is possible to identify most ants in New Zealand. It is not particularly scientific, but for many people it is easy to use colour to help distinguish the different types of ants. Here we group the main pest ants in to either black ants or brown ants.

Black Ants

Black House Ant

Green Head Ant

Tyrant Ants

White Footed House Ant

Brown Ants

Argentine Ant

Big Headed Ant

Pharaoh Ant

Red Imported Fire Ant

Ant Identification

Working out what type of ant you are looking at is difficult. Identification is very challenging due to their small size.

Successful identification uses size, colour, head & jaw shape and the petiole number and shape. (The petiole is the connection between the thorax and abdomen).

For most homeowners, starting off as to whether it is a black or brown ant is the normal starting point, and that’s how we’ve grouped the species on this page.

If you can catch or kill an individual and look under a magnifying glass you can compare to one of the images above. Click on one of the images above to get additional information to confirm identification.

Life-Cycle

Ants are social insects, with different castes having different roles within the colony. The queen is the most important caste in the nest as she lays all the eggs. They go through a complete metamorphosis which means after hatching they develop through a number of larval stages before passing through a pupal stage to become an adult.

Ant Eggs

Eggs are small white / translucent and oval shaped. They are often stuck to each other in clumps.

Ant Larvae

Larvae look like small, segmented maggots, typically white / translucent or cream in colour. They are not particularly mobile and if they need to move they will be carried by workers.

Ant Pupae

The pupae are typically cream, oval shaped sacs a bit larger than the adults. These are often assumed to be ant eggs to the untrained eye, but they are a lot bigger.

Worker Ants

All workers are female. They will often have different roles within the nest, such as looking after the nursery (eggs and larvae), excavating the nest, defending the colony or foraging. Typically, they change their roles as they become older – with the older individuals taking on the foraging responsibilities. Workers can live between 1-3 years, depending on the species.

Soldier ants

Some species have a specialised soldier caste. Typically, they will be larger than workers often with larger heads / jaws. If a species does not have a soldier caste, the defensive responsibilities of the colony are carried out by the workers.

Flying Ants

Flying ants or alates, are the winged reproductives – the new kings and queens that leave the nest to mate and start new colonies. These reproductives leave the nest in large numbers as part of a nuptial flight, which takes place in late spring and early summer on hot, humid days. They mate in the air and lose they wings shortly after landing. The males die and the queens move off to find a suitable location to start a new nest.

In some species, additional female reproductives (without wings) are produced. They support the egg laying of the original queen when the colony gets beyond a certain size or the original queen dies. Such reproductives can also start new nests through the process of budding, when they leave the original nest with a small amount of brood and workers to set up a new nest nearby.

Queen Ants

The queen ant is the most important ant in the colony as she lays the eggs. Sometimes there are multiple queens or reproductives in the same colony. To kill the nest it is necessary to kill the queen or all the queens in the colony, so that the colony loses its egg laying capacity. The queen is the most long-lived individual in the colony and can live for over 20 years.

Ant Nests / Colony

A nest is a single entity, but a colony may consist of one or more nests. Different species have different colony structures, varying in the number of nests and queens in the colony. There are three general nest structures:

Single nest, single queen (monodomous, monogyne)
Single nest, multiple queens (monodomous, polygyne)
Multiple nests, multiple queens (polydomous, polygene)

The serious pest species – the invasive ants – have a multiple nest, multiple queen colony structure, and it is one of the reasons why they are so successful in invading new areas. Their high reproductive rate allows them to spread rapidly and dominate areas. Over time they can create “super colonies” spread over hundreds of kilometres. This makes it virtually impossible to eradicate invasive ant species from a specific area, as even if they are eliminated from a defined area, they will re-invade from surrounding areas.

Understanding the nest / colony structure and likely nesting sites for the ant species causing a pest control problem is essential understanding in deciding on the appropriate ant treatment.

Key Behaviours

Ants are social insects and display a wide range of amazing and complex behaviours.

From a control point of view, understanding their foraging behaviour and food preferences is important information when deciding on which ant bait to uses in a control program, where to place the ant bait and how much bait to apply.

[Phil to check if there is an article on ant bait application? If not write one]

When it comes to food, foragers are able to remember good and bad for weeks, even after a single exposure – ants have a long-term food memory!

Ant Bites

Although generically called “ant bites”, some species bite, some ants sting and some can do both. Strictly speaking a bite occurs when the ant closes its jaws on the skin and sting is when an individual injects venom from its stinger at the end of its abdomen. It’s the sting that has the potential to cause the most pain. The venom contains a number of chemicals including proteins. It is these proteins that can cause the severe allergic reactions when stung by some species, such as the green-head ant, which can result in a long-lasting itching afterwards.

For most stings, applying ice to the affected area provides some relief, but for those that suffer severe allergic reactions or experience multiple stings, it is important to seek immediate medical attention.

How to get rid of ants...

Most homeowners find it tempting to try and rid of an ant problem with a bit of DIY pest control, but find it frustrating that they often don’t succeed. Often this is because spraying the ants only kills the ones you can see – there are plenty of other ants back in the nest which can replace them and so the problem quickly returns.

Professional pest managers succeed where homeowners generally fail in eliminating ant problems, as they can access a range of specialist ant control products that are not available to the general public. Combined with their ability to identify the species causing the problem and their knowledge of their nest structure and behaviour, they can design a suitable treatment program.

Typically, their treatment will depend on the species and location of the problem, for example

Ants in the house
Lawn ants
Ants in pavers

For ants in the house the primary objective is to eliminate them out of the house and prevent them re-entering the building. For ants in the lawn it is important to kill the nests. For ants digging up pavers a strategy of killing the nest or excluding the ants from the area works well.

Ant Products

Pest managers will normally use a combination of products to get on top of an ant problem. They will often use sprays to keep the ants out of the house or treat a particular area and baits to eliminate the nest.

They use specialist ant sprays to treat areas and around the perimeter of buildings. Sometimes they use repellent sprays which create a “barrier” to prevent entry, sometimes they will use specialist non-repellent sprays. These non-repellent sprays are designed to kill ants that walk over the treated area. In addition they are relatively slow acting (which is a good thing!). This allows the ants that walk over the treated surface pick up some of the insecticide on their body and pass it on to they nest mates during normal contact, therefore magnifying the effect of the treatment.

(For the really technical, you may ask the question about whether insecticide resistance is an issue in ants, making some products less effective? Although insecticide resistance can be an issue with bed bugs and German cockroaches, there is little evidence of insecticide resistance in ants.)

Sometimes when treating large areas, instead of using sprays, pest managers will use insecticide granules (not baits, but insecticide treated sand). These are often used when dealing with coastal brown ants.

To get lasting control it is important to kill the nest or nests causing the problem, which means killing the queen or queens, as they are producing all the eggs. If you can’t find the nest to destroy it physically or through spraying, you need to use ant baits. Although ant baits will kill the nest causing the problem, it won’t stop new ants moving into the area in the future.

In cases of severe infestations pest managers may need to make more than one visit. If you live in an area infested with one of the invasive species, such as the Argentine ant, it is likely you will need regular treatments to keep them under control. For other treatments, the pest managers will often guarantee they will eliminate the problem and offer a warranty or service free period against further ant problems for a set duration.

How ant baits work?

To get lasting protection from ants is it necessary to eliminate the nest. To do this you need to kill the queen or queens in the nest, as they produce all the eggs. If you don’t kill the queens, the queen can always product more workers to replace any you kill and the nest will recover. The best way to go about eliminating an ant nest is to use baits.

Ant baits consist of an attractive food source and slow acting insecticides. Ants feed on the bait, take it back to the nest and feed it to other members of the nest, including the queen(s). It needs to be slow acting so that it can passed around the nest before the ant realise it’s not good for them. By the time they do, it’s too late. As long as enough bait is applied relative to the size of the nest, small nests should be eliminated in 1-3 days and larger nests within 1-2 weeks. However, one of the tricks in successful ant bait treatments is choosing the best bait for the ant species of concern, as typically different ant species like different food sources – sugar, protein or oil/fat.

When dealing with invasive ants, although baits are very successful in eliminating individual nests, the problem is that there are often a large number of nests in an area, all part of the same colony. Therefore, when dealing with invasive species which may infest large areas and have multiple nests as part of the same colony, it is often necessary to use a combination of sprays and baits… and also require regular re-treatment to keep the numbers down (as complete elimination is often impossible).

How to Prevent an Ant Infestation?

There’s not much you can do to prevent an outdoor ant problem (other than get a professional treatment), but a few of the standard pest prevention techniques will minimise the chances of them becoming a problem indoors.

Good hygiene is critical

clean away split food and dirty dishes straight away

ensure rubbish is put in secure containers

don’t leave pet food in bowls on the ground

Keep food in sealed containers
Seal any small entry holes in the exterior walls / around doors and windows
Avoid having garden beds next to the house also helps

Remember they will also look to move indoors during the warmer months; during hot dry periods in search of water, or during lengthy periods of heavy rain for a dry nesting site.

Ant Control FAQ

What is the most effective way to control ants?

The best treatment for ants depends on the species and to a degree, depends on where the problem is. Most pest professionals will use of combination of baits (to kill the nest) and specialist ant sprays to prevent the ants coming into the house.

How long does it take to get rid of an ant problem?

After a professional ant treatment, you should see a big drop in ant numbers after 24 hours, but if baits are being used, it will take longer to kill the nest. Typically, a nest will be completely eliminated with a bait within 3-7 days. However, if it is a major infestation or large colony, it could take up to 2 weeks, and sometimes a second application may be required.

How long does an ant treatment last?

If a spray is being used to keep ants out of the house, it will typically last between 6-12 weeks, depending on the amount of sun and rain it received. However, most professional will provide a longer warranty, sometimes 6 months or more. This will depend on the species, but they can offer a longer warranty as they normally carry out a range of actions, not just a spray to eliminate the ant problem.

Is there a way to permanently get rid of ants?

Yes and no. To permanently get rid of ants, you need to destroy the nest and this can be done with baits or if you can find the nest, through directly spraying with insecticide. However, there will also be plenty of other ants ready to move into the area. Therefore to keep the yard clear of ants or prevent ants getting into the house, regular treatments will be required.

Which are the best ant products? Or Which is the most effective ant killer?

Ant baits are generally seen as the best (or smartest) and products as they kill the nest. However, it is important to choose the correct ant bait for the species in question – different ant species have different food preferences so its important to choose the bait to match. There are also a range of specialist ant sprays, which are only available to professional pest managers. These are classed as non-repellent sprays. They aren’t designed to repel the ants and create a barrier, rather they create a treated zone which the ants walk on, picking up the insecticide. Not only does this kill the ant in question, but the ant can also transfer the insecticide to other nest mates, magnifying its effect.