Controlling other ants
Before undertaking a costly and labour intensive management programme it is important to evaluate whether the nuisance caused by the ant warrants the effort of controlling it. There are three main categories of problems caused by ants: social, agricultural and environmental. Details of ways to assess these problems can be found in assessing impacts.
Five things you need to know
There are five key pieces of information required to effectively manage an invasive ant: what species it is, understanding its life history and lifecycle, what food the ant prefers, how abundant the ant is, and what time of day they are most active.
Identification: the more information you know about the ant, the less work you have to do to figure out how to manage it.
Life cycle: understanding the ants life cycle is necessary to choose an appropriate time to perform management. You must only treat with pesticides when larvae are present.
Food preference: assists you to choose treatments that are likely to be attractive to your target species.
Abundance and distribution: knowing whether the ant is abundant and how it is distributed in the environment (patchy or everywhere), helps you decide on the type of treatment.
Peak foraging: you need to time your treatment to coincide with peak forager abundance (when the workers are hunting for food). This will maximise the amount of bait collected and reduce the amount of bait left in the environment.
What is the information used for? Once you have this information, you can decide on a treatment option.
Identifying ants can be a difficult business. For example, the white footed house ant, a common household pest in New Zealand was formally identified in 1958 as Technomyrmex albipes. The ant is a nuisance that gets into peoples’ houses, forming long trails, raiding pantries and farming pests in the garden. Nearly fifty years later, in 2007 a researcher studying Technomyrmex found that every single specimen of this pest in New Zealand had been misidentified. The ant was, in fact, Technomyrmex jocosus, a different species altogether.
Irrespective of the name, people worked out how best to treat the ant and have been able to control it to some degree to minimise its negative impacts. This is because all the ants have a similar lifestyle.
Understanding the ants life cycle is necessary to choose an appropriate time to perform management.
Ants have a unique lifecycle compared to most other insects, which influences the methods needed to kill an entire colony. The lifecycle of an ant is called complete metamorphosis. It is the same kind of lifecycle butterflies have.
|Eggs are laid by the queen, and then hatch into larvae.
Larvae grow and are fed and cared for by the workers.
The larvae then pupate, often covered by a white or brownish cocoon, and the workers stop feeding them.
Then a new worker emerges from each cocoon
Workers are produced all year round in warmer regions, while reproductives (queens and males) are produced once a year, often at the beginning of the rainy season.
Only two of these four life stages (larvae and adults) eat. This means there is little point in distributing bait in the environment before eggs are hatched or when the new ants are in their pupal stage.
Yellow crazy ant workers tending to larvae and pupae (© Meghan Cooling)
If you are able to find a nest of the target ant species, look inside. If there are only eggs or pupae present wait before poisoning.
If there are eggs, larvae and pupae present it suggests the ants breed all year round and it is okay to go ahead with treatment.
Depending on your management goal you may have to treat more than once if the ants breed all year round.
To choose an appropriate bait, you must first understand the target ant species food preferences. This is because treatment products for ants are a combination of a pesticide and an attractive matrix. The matrix is usually some combination of sugar and protein.
|Ants can be broadly divided into two groups based on their food preferences; “sugar ants” and “meat/grease ants”.
Like any generalisation, there is considerable variation to this rule and an ant species’ dietary preferences may vary seasonally or according to their life history.
For example, prolonged periods of rain may dilute environmental sugar sources such as honeydew or nectar, which may lead to an increase in colony level demand for sugars. Demand for protein may increase shortly after eggs have hatched, as ant larvae require protein to grow to the optimum size for pupation.
You need to choose a treatment product with the right matrix for the ant you want to manage.Before buying a commercial bait it is a good idea to do a food preference test using lures.
Place a combination of sugar (e.g. cotton wool or toilet paper saturated in a thick sugar syrup (mix sugar with water until the sugar dissolves), or a small amount of liquid honey or jam) and protein (e.g. peanut butter, cat food, tinned tuna or oily fresh fish) onto small pieces of card or paper.
Distribute the cards through the infested area. Place five to ten lure cards at each of three or four discrete sites in the infested area.
As some of the food lures may dry out and become less attractive to the ants, the lures should be placed in a shaded area out of direct sun.
Leave the cards for up to an hour before returning to check them.
A similar approach can be used to test the attractiveness of different treatment products.
Example of card with food lures (© Allan Burne)
Bait card with treatment products (© Kirsti Abbott)
Record the data for each card in a table like the example below. Other ants could be attracted to the lures as well - so make sure to record data for the target species only. The averages at the bottom of the table indicate that the ants are most likely to consume a protein based bait.
|Site 1 (by school)||Date 23/11/2015||Bait out 5 pm||Checked 6 pm|
|Bait type||Sugar water||Honey||Cat food||Peanut butter|
|Card number||Number of ants||Number of ants||Number of ants||Number of ants|
If one bait type (e.g. the sugar water) is more favoured in most of the cards, it is a good indicator that the ants will be attracted to that type of bait.
If the ants appear to be evenly distributed on both bait options (protein and sugar) it may reflect a more generalist foraging strategy and a mixed bait is likely to be the best option.
Understanding the bait preference of the target ant increases the probability of successful management. The pesticide summary shows the matrix composition of various commercially available ant control products as well listing their limitations and potential environmental impacts.
Knowing whether the ant is abundant and how it is distributed in the environment (patchy or everywhere), helps you decide on the type of treatment.
Not all baits are distributed in the same way. For example, granular baits are often “broadcast” using manual spreaders, while paste baits are applied in small quantities at fixed intervals using a caulking gun or syringe.
Broadcast baits cover large areas at a pre-specified application rate and require a “critical mass” of foragers to take enough granules.
If there are too few ants, it is likely the bait will be left in the environment. The unused portion will either remain in the environment until it breaks down, is washed away by rain (potentially contaminating water ways or lagoon systems) or is eaten by non-target species. It is also a waste of time and money. For this reason it is important to estimate ant abundance before each round of treatment.
Distribution can be quickly assessed using a visual survey of the entire area and recording presence / absence points. This might underestimate ants when they are low abundance as they won't be obvious. But when ants are at high abundance, visual surveys are adequate.
You need to time your treatment to coincide with peak forager abundance (when the workers are hunting for food). This will maximise the amount of bait the ants collect and reduce the amount of pesticide left in the environment.
Foraging behaviour in ants may be affected by temperature, rainfall or other environmental conditions, so it is best to collect these data on a "typical" day i.e. a day that is not unusually hot, cold, rainy etc. for the time of year.
To assess both general abundance and peak abundance during the day, multiple attractive lures are used, depending on the food preference, which you have already assessed.
The lures are placed on cards within a pre-defined measurement area and visited regularly over a fixed period.
Typically, five to ten lures are placed within a 20 x 20 m quadrat and visited over a 24 hour period.
Visits may be hourly, two hourly, three hourly or four hourly.
At each visit the number of ants of the target species are recorded in a tally.
Dependent on the size of the infested area multiple quadrats, each containing five to ten lures, should be employed. The lures may need to be replenished as the ants eat them.
The table below shows an example of counts of ants over a nine hour period.
|Lure 1||Lure 2||Lure 3||Lure 4||Lure 5|
The results indicate that peak forager abundance occurs between 8:00 and 11:00 am. Lure 3 has consistently higher counts than the other lures, which may indicate the presence of a nest nearby. Foraging activity appears to decline in the afternoon (possibly because of temperature). The results suggest that morning is the best time to deploy baits.
The information collected above is used to help you choose treatment options.
If you are able to positively identify the target species, the first step is to ensure it is not one of the five worst ants in the Pacific. If it is one of the worst five assess the impacts then seek help. If it is red imported fire ant or little fire ant seek help immediately. If the problem species is not one of the worst five, then either seek expert advice or research online to see whether it has been successfully managed elsewhere, particularly in environments similar to your own, as this may offer a model treatment applicable to your situation.
Only use pesticide treatment when larvae are present. Some species will have all life history stages present at the same time. In this case it is advisable to bait more than once two to three months apart to ensure any queens that were in their pupal stage during initial round of treatment are killed in the second phase of treatment.
If they are treated too frequently, ants may associate bait with sickness in the colony and stop collecting it. To avoid this “bait shyness” it is advisable to leave between eight weeks and three months between treatments.
Choose baits that are likely to be attractive to your target species; protein based baits for meat/grease ants or carbohydrate baits for sugar ants. This table lists a selection of commercially available baits, the composition of their attractive matrices and some of the considerations associated with their use.
You should be aware that ants’ food preferences can change seasonally or in line with the particular phase of the colony life cycle. For this reason, food preference tests should be conducted as close to the commencement of treatment as possible.
Abundance and distribution
If the ants are at low abundance or patchily distributed consider whether the ants’ impacts (or potential impacts) are sufficient to warrant management. For example, yellow crazy ants may be present at low abundances without exerting any noticeable negative impact on agriculture, the environment or peoples’ day to day lives.
However, if you have the resources and the inclination to proceed with management of ants at low abundance, it may be better to avoid using broad range broadcast baits.
Alternatives such as paste baits or localised treatments should be considered in order to minimise the amount of pesticide left in the environment.
Time your baiting to coincide with peak forager abundance. This should maximise the amount of bait collected by the target species and reduce the amount of bait left in the environment.
Peak foraging periods for ants rarely coincide with the highest temperatures of the day, but in those cases where they do, choice of bait should be considered accordingly. Many paste baits have a tendency to dry out at high temperatures or in direct sunlight, reducing their attractiveness and effectiveness.
Abbott, Green, O’Dowd. 2014. Seasonal shifts in macronutrient preferences in supercolonies of the invasive yellow crazy ant Anoplolepis gracilipes (Smith, 1857) (Hymenoptera: Formicidae) on Christmas Island , Indian Ocean. Austral Entomology 53:337-346