How to make a pitfall trap to catch insects and other minibeasts

By Lisa Hendry

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 trowel
a yoghurt pot
a tray
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 gardens 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:

A dark, segmented millipede curled around a leaf.

Pill millipede (Glomeris marginata)

This millipede is up to 2cm long and curls into a small ball if threatened. Two pairs of legs per segment distinguish it from the pill woodlouse, which only has one pair per segment.

A long, dark brown centipede with long, lighter brown legs, crawling along the ground.

Stone centipede (Lithobius species)

This garden regular hunts around compost heaps and under stones. When fully grown it has 15 pairs of legs along its broad, brown body and is up to 3cm long. It has long antennae and hind legs

A small, grey-brown woodlouse with two off-white dots marking some of its rear segments.

Common shiny woodlouse (Oniscus asellus)

Like other woodlice, it has seven pairs of legs and an oval-shaped body divided into multiple segments. It is typically grey or brown with pale, irregular patches. Adults are glossy, but juveniles have a rough texture.

Two grey woodlice crawling along the ground. Their segments are covered numerous in tiny bumps.

Common rough woodlouse (Porcellio scaber)

This woodlouse is usually grey, but some can be more orange, brown or mottled. Tiny bumps on the exoskeleton give it a rough appearance.