Water-filled pan trap in farmland

Water-filled pan trap on farmland

Pan trap contents after 6 hours

Pan trap contents after 6 hours

We have put together answers to a few questions you might have about the FIT Counts or 1km survey – please get in touch via poms@ceh.ac.uk if your question is not answered here!

How often should I carry out FIT Counts?

There is no fixed rule about this, and even a one-off FIT Count will help provide useful data for our overall analysis. However, if you can do repeat counts over time at the same location this is especially useful. This could be once a month, once a week or even once a day – it’s entirely up to you! You don’t need to use the same target flower every time (and it’s fine to move the exact position of your count from one group of flowers to another).

Why is pan-trapping necessary?

Trapping is frequently used to monitor insect populations. This is partly because it can provide consistent, statistically valid results with less of the bias that is inevitably introduced by human observers; and partly because for many insects accurate identification to species level can only be achieved if specimens are examined under the microscope.

PoMS is using pan traps for our 1km square sampling. These are small plastic bowls painted white, yellow and blue, filled with water and a little unscented detergent to reduce surface tension. Insects are attracted to the bowls in the same way as they are attracted to flowers and get trapped in the water.

The PoMS pan trapping protocol has been carefully designed to minimise the number of insects caught, while still sampling enough individuals to measure changes over time. Typically we only catch 3-4 bees and hoverflies per set of three pans during a 6-hour pan trapping survey, though these numbers vary depending on various factors including location and time of year. There are studies showing that overall insect populations are not damaged by trapping at the scale and frequency of surveys like PoMS. The data provides robust evidence for change in insect abundance that can be used to inform conservation and environmental policy.

BBC Radio 4 recently produced an insightful programme in which several eminent entomologists talk about why it’s sometimes necessary to kill their subjects for the sake of science.

What happens to the insect samples?

Insects from the PoMS 1km square samples are stored in small tubes of alcohol and returned to the CEH laboratories for subsequent analysis and curation. This includes a full count of each insect sampled in the pan traps, broken down by species group. All bees and hoverflies from the samples are being further examined and identified to species level.

Can I add another 1km square to PoMS?

For now the PoMS surveys are being undertaken across a fixed set of 75 random stratified 1km squares across Britain, designed to be able to detect changes in insect numbers over a 5-10 year period. We do not anticipate adding to this number in the immediate future. The methodology we are using is available and could be applied in additional locations. If you are planning to do this we would be keen to hear from you. Although additional squares cannot be counted within the main set of PoMS data, they would form an interesting extra comparison.

Can I record the species I see?

For the FIT Count we only ask for insects to be identified to species group, and we are more concerned with the numbers of insects than with the species. But for any species that you are able to identify, either during the count or at any other time, the records will be welcomed by the recording schemes for the various groups (separate webpage to follow) or via iRecord.