Visual surveys

Visual surveys can be undertaken as part of surveillance, delimiting and monitoring of ant abundance and distribution.

Surveys for most ants should be done when the heat of the day does not stop them foraging. One exception is little fire ants, which forage all day and all night.

Visual surveys for surveillance : Visual surveys for delimiting & monitoring

Visual surveys for surveillance

When undertaken periodically visual surveillance of high risk and high value areas is a cost effective means of actively monitoring for invasive ant incursions. All that is needed is a notebook and pen or pencil, and the ability to identify the ant being surveyed. Surveys might be taken annually, bi-annually, quarterly or monthly. The interval will depend on how many people you have available to survey, together with the risk of invasive ant incursion.

The boundaries of the area of interest should be established and mapped if possible.

The area should then be searched fully, paying particular attention to areas that ants are known to favour:

1. Tree trunks, forks, hollows and the bases of trees
2. Flowers and extra-floral nectaries (EFNs), particularly nonu / noni
3. Shrubs, low vegetation and plant re-growth
4. Building edges and foundations
5. Hard seal (concrete/asphalt) slab edges
6. Cracked concrete/asphalt and junctions between pavers
7. Disturbed sites
8. Drains and culverts
9. Electrical generators and fittings
10. Exposed rocks
11. Loose gravel and soil
12. Grass areas, isolated weeds and road margins
13. Hot water pipes and heaters
14. Underneath logs, stones, concrete rubble, timber and debris
15. Plant pot bases
16. Rubbish piles
17. Shiny/corrugated surfaces
18. Vertical surfaces, poles, fence palings and wooden structures

If evidence of an invasive ant colony is found, collect a sample for identification and record the location.

Place a marker of some kind close to the place where the ant was found. For example, flagging tape, a colourful plastic bag, or a piece of rope well tied to a coconut tree, fence or post – these would be easily found.

Also, record any information that could help further investigation. For example, if ants are close to a breadfruit tree located behind the church, take note of this information.

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Visual surveys for delimiting & monitoring

It is important to find out the distribution and abundance of the target invasive ant species in order to plan any treatment, and follow up on the success of treatment (monitoring).

A visual survey is a simple and effective way to establish the presence or absence of the target species in a given area.

You will need a notebook to record the work, some flagging tape, ribbon or other means to mark locations, and a GPS (if available).

A note on measuring distance

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

Surveys (and monitoring) 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 centimetres 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.

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Dividing the area

This example is based on Atafu village motu, Tokelau. For surveying, the motu was visually divided into three segments (separated by red lines). Each segment has multiple survey tracks.

The tracks in the example are approximately 50 m wide and are placed so that they stretch from the lagoon side to the ocean side of the motu.

Having clear landmarks, or a consistent direction of travel (e.g. North to South to North) at the beginning and end of each track helps in navigation on the ground.

Each survey track is assigned a number for recording. It is important to record which survey track(s) invasive ants are seen in, in order to plan any treatment.

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Atafu village motu divided into forty-four 50 metre wide survey tracks for visual survey by a team of five surveyors (© Allan Burne, Pacific Biosecurity / Google Earth)
The tracks in the example are 50 m wide because they will be surveyed by five people (surveyors) spaced 10 m apart.  

If fewer people are available make the track narrower and have more of them.

So if there are only three surveyors divide each block into tracks that are 30 m wide and once again space the surveyors at 10 m intervals.

Conducting the survey

The surveyors move in a line parallel to each other from one end of the survey track to the other. Each surveyor checks the ground for the target ant species and checks any favoured places that may harbour ant nests.

The surveyors should generally be careful not to disturb any nest while searching as this may promote budding. An exception is for little fire ants (Wasmannia auropunctata). For these ants disturbance of the litter layer, soil or infrastructure at assessment points is considered good as it stimulates ant activity.

 
Five people, spaced approximately 10 m apart move from one end of the survey track to the other (red lines) looking for invasive ants (© Allan Burne, Pacific Biosecurity / Google Earth)
The surveyors should also check any nonu / noni or other fruit or flowers. Ants will likely be found foraging on them if they are present in the area. Similarly any trees should be checked for ants trailing up and down them.

One surveyor needs to be responsible for recording where ants are observed on a record sheet, aerial image or map. The track number should be recorded, and where the ants were found. 

If very few ants are found it would be helpful to mark the area for spot treatment.

The group moves back and forward throughout the survey area until it has been covered.

The surveyors move in a line through each survey block.

When the surveyors  reach the end of the block, they move into the next block, turn 180° and move through the block in the opposite direction to the previous block.

 
At the end of each survey track the team regroups spaced 10 m apart as before and proceeds with the survey moving in the opposite direction (© Allan Burne, Pacific Biosecurity / Google Earth)

Spacing is important

It is important to maintain good spacing, by ensuring the survey team are equally spaced and they cover the whole area. This can be achieved using the technique shown on the right.

When the survey team reach the end of a survey block (#1), the surveyor closest to the next un-surveyed block (surveyor #5) moves approximately 10 m toward the next survey area (survey block #2) and turns around 180° (e.g. if they were facing the ocean they should now be facing the lagoon or vice versa).

The rest of the team space themselves out 10 m apart in the new survey track and continue the survey as before.

You can find more information about visual surveys in the Atafu Management Plan.

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Five surveyors move from one end of each survey block to the other (© Allan Burne, Pacific Biosecurity)

Recording data

Data from each survey track should be recorded in a table (example below also) with the track number, if the target species was seen, the number of times it was seen along the track, abundance, if lures were used, and location and general notes about the observations.

Track number Target ant species Present (Y/N) Number of times seen on track Abundance (at one spot) * Lures used (Y/N) Location notes General notes
1 Yellow crazy ant N          
2 Yellow crazy ant Y 10 H N high around the centre of the track follow up with spot treatment of AntOff
etc              

*In this example for yellow crazy ants, abundance was measured using card counts. Low = 1-10 Medium = 11-29 High = More than 30

When no ants are detected during a visual survey, attractive lures should be used to confirm absence, as ants at low abundance can be difficult to detect with visual surveys alone.

Information sources

Doherty. 2013. Delimiting surveys for invasive ants. Pacific Invasives Initiative, Auckland

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

content reviewed by Phil Lester August 2016, Souad Boudjelas November 2016
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