How to make a pitfall trap to catch insects and other minibeasts
Would you like to find out what small creatures are crawling around your garden? Follow our instructions on how to set up a simple pitfall trap.
What is a pitfall trap?
A pitfall trap is a simple device used to catch small animals - particularly insects and other invertebrates - that spend most of their time on the ground.
In its most basic form, it consists of a container buried so that its top is level with the surface of the ground. Any creatures that wander nearby may fall in. Any that can't escape by climbing, jumping or flying out will remain trapped until you release them.
How to make a pitfall trap
You will need:
a yoghurt pot
ID guides (optional)
1. Choose a location for your trap on flat ground near vegetation.
2. Use a trowel to dig a small hole.
3. Place a clean yoghurt pot in the hole. Fill in any empty space around the pot with soil. Make sure that the top of the pot is level with the ground, or you won't catch anything.
4. Leave your trap overnight. If you prefer to leave it during the day, check it at least every few hours.
5. Empty the trap into a tray to see what creatures wandered in. Use ID guides (books, online resources or apps) to help you identify what kind of invertebrates they are.
6. Record your findings: make a note of what you caught, the date and location. You could also draw the creatures or take photographs.
7. Carefully release the creatures, returning them to a safe, sheltered place.
8. Return the area back to how you found it.
Top tips from our ecologist
Museum scientist Sam Thomas regularly sets up pitfall traps in the Museum's Wildlife Garden as part of biodiversity monitoring of the area. He has these tips for anyone who wants to try setting up their own pitfall traps:
- It's really important that your container is flush with the ground. Even a millimetre lip can have an impact and stop things from falling in.
- Water will ruin your trap, so don't place it at the bottom of a slope where water could run in.
- If it looks like it might rain, make a small 'roof' for your trap. Balance a small piece of wood or stone on four small stones (one for each corner). Leave room for bugs to slip in. You could also add small holes to the bottom of your pot to let water drain away.
- You're most likely to catch something interesting if you place your trap somewhere with varied vegetation. Next to dead wood or in flowery grassland would work well. You're unlikely to find much in the middle of a normal lawn with short grass.
- It is a good idea to add some leaves to the bottom of your pot. This gives the creatures somewhere to hide in the trap and reduces the likelihood of larger carnivorous invertebrates (such as large beetles or spiders) preying on the smaller ones.
- Since many invertebrates are active at night, it is best to leave your trap overnight. Check your trap in the morning, before the day starts to get warm. Don't leave it any longer, or you might harm the creatures you catch.
- If you do want to set your trap up during the day, it is important to check it regularly - at least every few hours and ideally every hour - to avoid creatures dying of heat or exposure.
Insects and other minibeasts you're likely to catch
Pitfall traps catch ground-dwelling invertebrates, including insects.
The main creatures that are likely to fall into your trap are beetles, woodlice, millipedes, centipedes, earwigs, springtails and spiders that hunt on the ground. You'll possibly also encounter worms, slugs and snails.
Here are some of the more common UK invertebrates you might catch:
Any beetles in the trap are most likely to be ground beetles (Carabidae family) or rove beetles (Staphylinidae family). There are over 350 ground beetle species in the UK, ranging in size from two millimetres to three centimetres. Rove beetles are the most diverse UK beetle family, with more than 1,000 species recorded here. We've highlighted a few common ones below, but it is difficult to identify most to species level.
Ladybirds (Coccinellidae family) are unlikely to get caught in your trap, as they're strong fliers and tend to spend their time on plants feeding on aphids. But harlequin ladybird larvae are very common and you may well see some of these.
Experiments you could try
If you don't catch much on your first try, don't give up. Try placing your pitfall trap it in a different area near more vegetation. You could compare what and how much you catch in different locations.
You could also try adding bait to your trap. A banana may entice some creatures. Be careful not to leave the banana in the trap too long, though - you don't want to return to find things encased in decaying banana goo. Bear in mind you're likely to have a stream of ants moving back and forth to the banana.
Sam also has another suggestion:
'If you have access to fresh animal dung, such as guinea pig or rabbit pellets, you could put some of these in your pitfall trap.
'You might catch dung beetles, even in urban areas. These are quite different from the tropical species that roll dung balls. UK species instead live in the poo or bury it below ground.'
More than 50 beetle species in the UK depend on dung.
Identification guides and help
The iNaturalist app both helps to identify wildlife you photograph and contributes your findings to international scientific databases.
If you're in the UK and have trouble identifying the insects you find, you can also get in touch with the Museum's Identification and Advisory Service.
Buglife identification chart PDF (10.4MB)
Share your findings
If you would like your wildlife findings to be useful for science and conservation, you can upload your observations and photos to the Biological Records Centre's iRecord. Your findings will then be available to national recording schemes.
Sun beetle © entomart via Wikimedia Commons