Monitoring is undertaken for three purposes:

  1. Evaluating treatment success: to evaluate the success of the treatments, monitoring of ant distributions and abundance is needed before and after treatment
  2. Evaluating if treatment is required: if treatment is not warranted because impacts are low or the problem is not urgent, monitoring of ant distributions and abundances is needed to assess if treatment should take place
  3. Monitoring non-target effects: to assess potential non-target effects of treatment, monitoring of local wildlife is needed before and after treatment, and measuring any potential effects of the pesticide on people

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

The video is also available in French.

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

1. Evaluating treatment success

Before and after each round of treatment, ant abundance and distribution and impacts should be assessed in the same way as for delimiting and assessing impacts.

Multiple sites should be chosen in the treatment area and visual surveys (at a minimum) should be done. If time, resources and funding permit, other assessments can also be done, such as card counts (for yellow crazy ants), pitfall trapping (for ants and other insects) and luring.

2. Evaluating if treatment is required

Even if treatment is not considered a high priority, the situation should still be regularly monitored so that any worsening effects can be detected. The frequency of monitoring will depend on the time, resources and funding available. Ideally, this monitoring should be undertaken at least every 6 months.

During each monitoring event, ant abundance, distribution and impact should be assessed in the same way as for delimiting and assessing impacts. One additional requirement is that areas outside the infestation need to be monitored in case the ant spreads.

One cost-effective way to have the monitoring done is to enlist the community to help. This also has the benefit of raising awareness.

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3. Monitoring non-target effects

To identify any non-target environmental effects of the treatment, surveys are conducted before and after treatment. The pre-treatment survey is conducted immediately before treatment, and the post-treatment survey is conducted no more than 5 days after treatment.

The follow up post-treatment survey is required to compare with the initial survey to see if there have been any noticeable negative impacts on animals other than the target ant species. The pre- and post-treatment surveys should be conducted along the same transects at the same time of day. Where possible, the pre- and post-treatment surveys should be conducted by the same surveyors.

These surveys simply count the number of living and dead non-target animals encountered along 100 m transects.

A note on measuring distance

It's important to have accurate spacing to make sure all the survey area is covered properly.

Surveys may be guided and measured with the assistance of GPS units. If GPS units are not available, distances can be figured out using pace lengths - the area covered when a person is walking.

The average male pace length is approximately 76 cm (0.76 m) and the average female pace length is 67 cm (0.67 m). So, by dividing 10 m by 0.76 m you can calculate that the average male needs to take 13 paces to cover 10 m. The average female needs to take 15 paces (10/0.67).

One person in the group (ideally the tallest) is the measurer. Measure the length of his or her pace length in metres and divide as above. Use the result to figure out the 10, 20 and 100 m distances used in monitoring. This Excel sheet is a helpful tool to check your calculations.

If you don't have a GPS, it is useful to mark the start of each track with some flagging tape, or piece of ribbon or cloth or spray paint.

If it is not possible to measure 100 m exactly, the start and end should be estimated. It is more important to be consistent between surveys before and after treatment.

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Running the survey

At least ten 100 m transects should be used as abundance of animals can be highly variable over time, particularly animals that move a lot, such as lizards and birds. 

The transects should include coastal areas (if applicable) as pesticides can kill fish.

The transects are ideally guided using a GPS unit. If this is not available it is suggested that the start points are established and marked using coloured tape, plastic bags or any other high visibility item available. The length of the transect is measured in paces as outlined above and the direction of movement is guided by compass. 

Two or more surveyors spaced approximately 20 m apart walk slowly in parallel straight lines through the area for 100 m. The surveyors record any insects (other than the target ant species), spiders, birds, crabs, lizards or fish they encounter and note whether they are alive or dead.

Ten 100 m transects within a treatment area. Transects are approximately 20 m apart. The transects are numbered. S indicates the start of the transect and F indicates the finish (© Allan Burne, Pacific Biosecurity / Google Earth)

All animals observed should be recorded in a table for later comparison. The surveyors should mark waypoints along the way, so that the transect can be followed again later. At these waypoints the surveys should stop for 10 seconds and observe and record any animals around them. 

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Recording data

Record data from each pre- and post-treatment surveys for each transect in a table like the one below in the form of tally marks (e.g. ||||). Be sure to record the date, transect number and time of day. The upper portion of the table is used to record animals on the transect before treatment. The lower portion of this table is used to record the observations in the post-treatment survey. The data collected is used to assess non-target effects of the treatment.

Before treatment
Transect number: Date: __ /__ /__ Time of day: ____ am/pm
Crab Spider Insect (other than target ant)
Alive Dead Alive Dead Alive Dead
Lizard Bird Fish
Alive Dead Alive Dead Alive Dead
After treatment
Transect number: Date: __ /__ /__ Time of day: ____ am/pm
Crab Spider Insect (other than target ant)
Alive Dead Alive Dead Alive Dead
Lizard Bird Fish
Alive Dead Alive Dead Alive Dead

A printable version of this table is available in pdf form.

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Monitoring health effects in people

If the treatment is being undertaken in an inhabited area, surveys should also be undertaken on any health effects.

Health surveys are useful to assess these possible effects. Sometimes surveys of this type need to have Human Ethics Approval - this will depend on the requirements of your employer or local regulations. But even if Human Ethics Approvals aren't required, it's important to consider what people are being asked (and the way the questions are being asked), how their privacy is maintained, and that they are fully informed about the end use of the information they are giving. Interviewees should never feel an obligation to answer any question and should be free to change their mind about participating.

Pacific Biosecurity's yellow crazy ant management work in Tokelau and Kiritimati includes health surveys, which you can use to base your own health survey on.

Information sources

Burne, Barbieri, Gruber. 2015-2019. Management Plan Atafu, Tokelau. Pacific Biosecurity Management Plan

Gruber. 2014. Environmental and Social Impact Assessment (ESIA) for Outputs 4 & 5 (management of yellow crazy ant incursions in Tokelau and Kiribati). Pacific Biosecurity assessment for New Zealand MFAT