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:

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.

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

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.

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.

Pill woodlouse (Armadillidium species)

It can be distinguished from the pill millipede by the number of legs per segment and its three small plates at the tail end.

Springtail (order Collembola)

These very abundant, tiny invertebrates feed on decaying vegetation. They are less than 6mm long. They have a tail-like appendage that they use to jump.

Money spider (Linyphiidae family)

Most of these tiny spiders are less than 5mm long. They build horizontal sheet webs to catch their prey, sometimes on low vegetation or depressions in the soil.

Wolf spider (Pardosa species)

These spiders hunt their prey on the ground. They grow to about 8mm long and are quite hairy, with a brownish body and brown, grey and black markings. There are several species that are quite hard to distinguish.

Woodlouse spider (Dysdera crocata)

Woodlice are the main prey of this spider. Its fangs are strong enough to pierce a woodlouse's hard exoskeleton, so it's also capable of giving people a painful, but harmless, bite. The similar D. erythrina is unlikely to be found in urban environments.

Common earwig (Forficula auricularia)

Earwigs grow to about 13mm and have a long, slim body, but their most recognisable feature is their pincers. Male earwigs have curved pincers, while females have straight ones.

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.

Harlequin ladybird larva (Harmonia axyridis)

With the exception of having six legs, the larvae look nothing like the adults they grow into. Their spiky bodies are orange and black, and up to 1cm long.

Violet ground beetle (Carabus violaceus)

This common garden species grows up to 3cm long and has a metallic purple sheen. Carabus problematicus looks similar but its fused wing cases have distinct ridges and dimples.

Blue ground beetle (Leistus spinibarbis)

In sunlight, this centimetre-long beetle has a handsome metallic blue body. It is a very fast runner, often found among overgrown vegetation in gardens.

Sun beetle (Amara species)

There are many similar Amara beetles. They are generally less than a centimetre long, with a shiny bronze or black bullet-shaped body.

Devil's coach horse (Ocypus olens)

At nearly 3cm long, this is the UK's largest rove beetle. It is often found in gardens under logs and stones, or among leaf litter. If it feels threatened it rears up its tail. Watch out for its painful but harmless bite.

Experiments you could try

If you don't catch much on your first try, don't give up. Try placing your pitfall trap 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's key to UK land invertebrates PDF (584KB)

NatureSpot has helpful image galleries for many species of invertebrates observed in Leicestershire and Rutland.

The Field Studies Council sells a variety of invertebrate identification charts.

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.

Nature Recording Hub

Discover how to record the wildlife in your urban environment.

British wildlife

Find out about the plants and animals that make the UK home.

Image credits:

Earwig courtesy of Francisco Welter-Schultes via Wikimedia Commons (CC0)