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Night life: how to spot insects in the dark

There is a huge variety of animals that are active after sunset. The absence of light can make spotting them a challenge, especially when it comes to insects.  

But by using a simple method, you can get to know your local wildlife and find out what nocturnal insects call your area home. 

Dr Gavin Broad, Principal Curator in Charge of Insects at the Museum, introduced us to the world of light trapping and explained how this simple and repeatable technique can help scientists keep track of the distribution of insect species.

Watch the video above to follow Gavin on a light trapping excursion and discover why you might want to try building one. Read on to find out how to create your own light trap.

Why try light trapping?

Light trapping is a great way to learn more about the wildlife living in your local area. It's easily repeatable and harmless to the insects involved. By gently capturing them in a jar, the insects can be released back into their habitat once they've been recorded.

It is a simple but effective way of collecting a lot of data in a short amount of time - though this does depend on factors like location and weather conditions.

By sharing the data that you collect on an excursion (even if it's just to the bottom of your garden) you can help increase our understanding of the geographic ranges of species and any changes in their distributions - you might even come across something rare or new to your area.

Scientists sometimes use light traps in the field to help them study nocturnal insect species

How to build your own light trap

Setting up a basic light sheet is relatively easy, requiring only a few items - you may already own some of them.

Insects see light wavelengths (colours) differently to us. They can see ultraviolet (UV), green and blue lights best. Red and infrared light are invisible to them, and they can't see yellow and orange very well.

A torch that produces UV or cool toned lights will usually work best in a light trap. If you choose to use a UV light, always refer to the manufacturer's safety guidelines before use.

How to make a light trap

To build a light trap, you will need:

  • an old white sheet
  • rope
  • string
  • tent pegs
  • a torch
  • a clear jar with a lid

1. Find an area to set your light trap up in. Ideally the space will have plenty of trees and be very dark, with as little artificial light or moonlight as possible. It's easiest to set up in the evening, whilst there is still a little natural light.

2. Assemble your light sheet. Tie the rope between two strong trees and hang the white sheet over it. Secure the base of the sheet to the ground with the tent pegs.

3. Using the string, hang the torch in front of the sheet and switch it on. Wait for it to get dark and for insects to be attracted to the light of your torch.

4. When an insect lands on the sheet, gently place a jar over the top of it. Carefully slide the lid under the jar to capture the insect.

5. Study the insect in the jar to try and identify what it is. You could use books, mobile apps and the internet to try and work out what species you have found.

6. Take photos of your find and share them online. You can find a selection of groups and websites to share your findings with below.

7. Carefully release your captured insects back into their natural habitat.

It is possible to buy light traps, but these can be much more expensive than building your own

Can you buy light traps?

If you'd prefer to buy rather than build a light trap, or would like to boost the effectiveness of your night-time insect spotting excursions, there are plenty of light traps and more powerful lightbulbs on the market. These are available from entomological equipment suppliers.

A box-like trap has the advantage of running overnight. These allow you to set them up in the evening and return in the morning. These types of traps can be rather expensive, however.

Where to share your light trap findings

Butterfly Conservation run the National Moth Recording Scheme and every county has a moth recorder. Additional information can be found on their website.

European Moth Night is an excellent time to get involved, with light trapping activities being run across the country. The next European Moth Night will be on 27-29 August 2020.

There are various recording schemes and Facebook groups that deal with other insects found at night. A couple that Gavin uses are the burying beetles (Silphidae) recording scheme, which has great identification keys, and the Facebook group Moth trap intruders (a closed group but requests to join are very welcome).

Observations and photos of insects can be uploaded to the Biological Records Centre's iRecord. Your findings will then be available to national recording schemes.

The mobile app iNaturalist both helps to identify wildlife you photograph and contributes your findings to international scientific databases.

If you're in the UK and having trouble identifying the insects you find, you can get in touch with the Museum's Identification and Advisory Service, which should be able to help. 

Nature Recording Hub

Discover how to record the wildlife in your urban environment.