Trapping the Spotted Fruit Fly

The Spotted Wing Fruit Fly, Drosphila suzukii, (known as ‘SWD’ for short) is a small but potentially devastating pest that attacks soft fruits. Here’s how to make a simple trap from a plastic bottle. You can then see if you have caught any fruit flies and send your results to an exciting citizen science project.

Making your Fly Trap

You will need:

  • A large empty clear plastic bottle (perhaps a fizzy drink bottle or squash bottle)
  • Apple cider vinegar (cheapest from a supermarket)
  • Washing-up liquid
  • String
  • Ruler
  • An auger, awl or large nail (2 mm to 3 mm diameter)
  • A magnifying glass OR a low power stereo microscope (OR a camera phone and some honey!)

What to do:

Start by watching this video by Chris Thomas of the Queckett Microscopical Club. It shows each step of making the fruit fly trap.

Step by step Instructions:

  1. This bit needs an adult to help. Carefully pierce 8 holes in the bottle more than half way up, using the augur or nail. Lie the bottle on a table or board. Hold it firmly at the bottom half and gently pierce with a sharp metal point or augur, through the upper side of the bottle towards the board. If the point slips, it should then go safely into the table or board and NOT into your hand. Make the holes 2-3 mm in diameter, to let in small flies. I used a sharp augur to pierce the plastic and then a wider diameter nail to enlarge the hole.
  2. Fill the upright bottle to ¼ to ⅓ with apple cider vinegar. The level must be below the holes!
  3. Add one or two drops of washing-up liquid.
  4. Screw lid back onto plastic bottle.
  5. Use the string to hang your baited trap from a tree/bush/holder at a suitable place.
  6. Leave the trap for one week.
  7. At the end of the week, seal up holes with sellotape.
  8. Swirl bottle gently and carefully pour the fly catch into a white / light coloured plastic dish. (OPTIONAL: strain the fly catch through an old metal tea sieve and then transfer the flies to clean water with a bit of vinegar in it to preserve them.)
  9. Record your results (see below).
  10. At the end of the experiment, wash and flush away the flies and liquid. Wash the plastic bottle thoroughly and recycle it. Don’t forget to wash your hands.

2021 Spotted Fruit Fly Survey

If you have caught some fruit flies, you could send your results to the 2021 Spotted Wing Fruit Fly Survey and help track the spread of this pest across the UK.

Drosophila suzukii on a ripe banana. Image credit: Flickr / Martin Cooper CC BY 2.0

The Spotted Wing Fruit Drosophila (SWD) is a pest in many parts of the world because it causes damage to soft fruits. It was first spotted in the UK in 2012 and this survey aims to find out how far it has spread. Counting and scoring the results from your trap will be really helpful and we will link your results with those from many other people. The more people who contribute, the more we can learn about the biology of this pest.

Fruit flies are small – only a few millimetres long – but can be identified by a couple of key features with a hand lens, low power microscope, or by using a mobile phone camera (see below). The male flies are easily identified by their characteristic wing spot. The females don’t have the wing spot but do have a vicious-looking saw-like egg laying organ (called an ovipositor) at their rear end.

You might like to use your fruit fly trap to catch Spotted Wing Drosophila over a week, count what you have caught and send the results to Chris Thomas of the Quekett Club at bulletin@quekett.org by the end of November.

The Club aims to collate all the results and publish them in the Quekett Journal, mentioning all participants who submit results.

Identification help

How to identify male and female Spotted Fruit Flies. Image credit: © Queckett Microscopical Club
  • Either use a magnifying glass or a low power microscope to magnify the catch. Don’t worry if you don’t have one – watch our video Turn Your Phone into a Microsope.
  • Fruit flies are very small, between 2 mm and 5 mm long. They are quite distinctive.
  • Use the pictures to help you identify the Spotted Winged Drosophila.
  • The male flies are obvious even to the naked eye – they are red-eyed fruit flies with a black spot at the end of the wing. Under magnification, they also have 2 spurs on their forelegs.
  • The female flies are best viewed under 10× to 30× magnification: they have no spots but their saw-like ovipositor (egg-laying organ) can be seen clearly. Once you have seen one, you will never be confused. They also have clear black and yellow bands on their abdomen.

Record your results and send them to the Quekett Club

You should include:

  • Name and address (or just your post code, if you don’t wish to be named as a participant)
  • Date when you emptied the fly trap
  • Total number of ALL insects/creatures in trap
  • Total number of ALL fruit flies
  • Number of male Spotted Wing Drosophila
  • Number of female Spotted Wing Drosophila
  • The Queckett club would love to see pictures of your catch, so please add them too
  • SEND YOUR RESULTS TO  Chris Thomas at bulletin@quekett.org by the end of November.

It’s really important to record and send in ALL results – even if you did not catch anything!

  • If you don’t catch anything, enter ‘Nothing’
  • If there are no Spotted Wing Drosophila, but you see other fruit flies, enter ‘Common Fruit Fly’
  • If you can’t decide if they are males or females, just tell us the total number of SWD

Make sure you send your survey results to Chris Thomas at the Quekett Club, but the team at Crunchy on the Outside would also like to see your fly traps and catches! Let us know how you got on by emailing us at hopelearning@oum.ox.ac.uk or using the Contact Us form.

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