Pitfall Trapping

 A few weeks ago, we did pitfall trapping around the UEA campus to investigate invertebrate biodiversity in different habitats with different management techniques, as well as trying out different techniques of pitfall trapping. It was interesting to use a very different style of trapping to the small mammal trapping I have previously written about - catching creepy crawlies instead of cute mice this time! In this blog I'd like to give an overview of the pitfall trapping process, as well as a comparison of how humane it is compared to our small mammal trapping.

What we did

There was a selection of sites across campus we had the opportunity to survey, but we chose to look at the butterfly meadow (sugars.skinny.plenty) and playing fields (tells.yoga.twig). This allowed us to compare grassland habitats with a lower and higher intensity of management. At each location, we placed two pitfall traps. One was unbaited, and the other was baited with vinegar to kill any insects trapped in it. I'll explore the ethical implications of this later on. To ensure we could relocate the traps the following day, we recorded the location on what3words as well as marking the location with a stick.


An individual pitfall trap - a plastic pot sunk into the ground in a hole dug with a trowel


Our marked pitfall traps in the butterfly meadow


Our marked pitfall traps in the playing field

What we found

The following morning after setting the traps, we collected the specimens and brought them into the lab to ID, using the taxonomic key. Here is what we found:

- A beetle (Tim!) in the baited butterfly meadow trap
- A woodlouse and a beetle larva in the unbaited butterfly meadow trap
- A millipede (Stuart!) in the unbaited playing field trap

These suggested that, as expected, the butterfly meadow was more biodiverse than the playing fields due to the more sympathetic management. More surprisingly though, we found more animals in the unbaited traps. I expected that as the lethal, baited, traps prevent individuals escaping, there would be more specimens caught in them in the morning compared to the non-lethal, unbaited, traps where insects may have been able to escape.

Baited vs unbaited traps

As with any form of trapping, there are important considerations around humaneness and ethics. The traps baited with vinegar have the obvious issue of killing any caught individuals. While this may arguably improve the effectiveness of pitfall trapping, it comes with moral issues as well as killing the very individuals we are trying to conserve, albeit any population-scale impact is likely to be small. The unbaited traps are not totally humane either though - animals are trapped, potentially for long periods of time without food. They may also be more vulnerable to predation, which would also reduce the effectiveness of the technique - checking the traps more regularly can help with these issues. This is all important because, while it may surprise you to know, many studies show that insects do have feelings! We therefore do need to have regard for looking after our little insect friends - I'm very happy we only caught one insect in our baited traps!

Despite all this, pitfall trapping remains one of the best ways of surveying the insect biodiversity of an area, and allowed us to see the effects of less management on the grasslands around the UEA campus.

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