Assessing the problem

Whether you are monitoring a problem ant species to decide when control treatments are necessary, determining the extent of an infestation prior to treatment, or evaluating the success of a management activity, you will need to assess the extent and impact of the species.

Before you undertake delimiting and impact assessment you need to identify the ant species if possible. 

Two key aspects to assessing the problem are delimiting (the boundaries of the infestation and abundance of ants) and assessing impacts (the environmental, agricultural and social effects of the ant). 

Once you know the boundary and impacts of the infestations you can decide on a management approach.

Delimiting : Assessing impacts


Whether you are delimiting the extent of an infestation prior to treatment or evaluating the success of a management activity, it is important to record consistent data about the identity, distribution and abundance of the target invasive ant species.

Four key techniques to help you achieve this include:

  1. Visual surveys are a quick way to find out if a target species is present
  2. Attractive lures are used to asess all the ants that might be present. Sticky traps use lures to detect ants that may be present. The difference between sticky traps and standard attractive lures is that ants cannot escape the sticky traps
  3. Pitfall traps as well as helping identify the limits of the ant infestation, pitfall traps can give you an idea of the impacts of the ants
  4. Card counts are used to quickly assess the abundance of yellow crazy ants. They could be used to assess other ants that have 'crazy' behaviour

We have created a video that outlines the methods of surveillance for invasive ants

The video is also available in French.

Surveillance methods for ants. The video is also available in French (© PIAT, Pacific Biosecurity)

The methods used for delimiting are very similar to those used for surveillance (visual surveys and baited lures).

A note on replication

Regardless of your delimiting method you need to include replication. Replication simply means having more than one sample of something. You need replication because there can be a lot of differences between single samples. This is variation, and can really affect your conclusions. For example, ant nests are not evenly distributed in the environment and placing pitfall traps near to one nest will result in more of those ants than other ants. So, to get a good sample of different ants, you need multiple pitfall traps in an area.

Replication is needed at all levels in your sampling design. For example for pitfall trapping, you need more than one pitfall trap in each transect or plot. You need to know that your results are sound. This is why you have many sites, many transects / plots within sites and many traps within transects / plots. This is called nested replication, and removes the effect of natural variation at different geographic scales (between the sites, between the transects and between the traps). At least two replicates at each level (site, transect / plot, trap) are recommended. The sites, transects and traps should be given names or numbers to identify them.

Assessing impacts

The introduction of an invasive ant species may result in negative impacts on agriculture, the environment and human well-being. It can be difficult to assess the impacts of the ant in some cases.

The ants may form associations with sap sucking bugs that damage crops and spread plant diseases. Ants are efficient predators and, at high abundance, can interfere with the breeding success of birds, kill chicks, crabs and reptiles as well as other beneficial insects.  Many invasive ants bite, spray acid or sting and can reach high numbers in new environments making it difficult for people to eat, sleep or work without ants crawling on them.

A less obvious hazard involves introducing an organism that allows ants that are already present at low abundance to rapidly increase their numbers. Such organisms include aphids, scale insects and mealy bugs, which produce honeydew that ants use for food. These pests can carry viruses and other plant diseases and are protected and farmed by some ant species resulting in the insects' numbers increasing, which in turn leads to significant crop damage and/ or loss of yield.

content reviewed by Phil Lester, Victoria University of Wellington, August 2016