Spotted Wing Drosophila survey experiment

Male spotted-wing drosophilaThe Quekett’s first large-scale venture into recording living specimens started in 2016, monitoring the spread of the invasive fruit-fly Drosophila suzukii (Matsumura) in the United Kingdom, and you can read about it here:

Quekett member Chris Thomas is now expanding the project by getting people outside the Club to participate as well.

The Quekett’s Spotted Wing Drosophila survey experiment is a citizen science project open to all. It suits individuals, schools and researchers, with or without a low power microscope. You can go directly there: or read more below first.

A reminder. Spotted Wing Drosophila is a fruit fly achieving global devastation of soft and stone fruits. The males are easily identified by eye due to the characteristic wing spot, with a hand lens or even on an enlarged photo. The females do not have the wing spot but do have a vicious-looking serrated ovipositor (egg laying organ), which is best seen under a low power stereomicroscope or by some other means of magnification beyond 15×. It is very easy to set up traps that mainly catch fruit flies. Counting and scoring results from traps really becomes useful when linked to results collected by others. We can learn a lot more about the biology of the pest if many people contribute.

Spotted Wing Drosophila banner

After the success of the Quekett 2016 Spotted Wing Drosophila trial survey (to be published in the upcoming Quekett Journal), I was inspired to set up a citizen scientist, public crowdsourcing version of the experiment. This was a direct result of attending the ‘Connecting the Crowd’ conference at the Natural History Museum in June 2017, where I gave a five minute talk on our trial, title ‘Who’s being eating MY strawberries!’ There is a wide range of citizen science projects, where contributors can help with anything from deciphering difficult to read dead sea scrolls to finding and identifying galaxies by shape. Keynote speaker Professor Chris Lintott recommended that I try iNaturalist as a platform for our Drosophila project.


iNaturalist is a flexible platform where contributors can add observations of flora and fauna. It also allows you to set up special interest projects.

To take part in iNaturalist, you need to register with a username and a password. After that you can either use your PC/laptop or download an app to your smartphone. You can take a photo of an insect/plant/other living organisms and submit this as an entry. If you can provide the following, you have a research grade entry.

  1. A picture
  2. A location
  3. An identification (to the best of your ability)

Once you have made an observation, others can comment, agree with your identification or suggest alternatives. If you use it for nothing else but observations, give it a go – it’s infectious!

The Quekett Spotted Wing Drosophila survey experiment

iNaturalist lets you set up special interest projects, which is what I have done for Spotted Wing Drosophila. This project tells you how to make a fruit fly trap out of common ingredients and materials, and how to identify male and female spotted wing drosophila in your catch. It asks you to give a range of information after you have done a weeks trapping. Anyone can join in! Go to:

About the project

Who’s been spoiling YOUR fruit? Take part in a real experiment. Suitable for individuals, schools, farmers and researchers. This is a NON-COMMERCIAL project.

Spotted Wing Drosophila (Drosophila suzukii, SWD) is a fruit fly pest that is devastating fruit grown around the world. Help us understand it better.

SWD is a plague to fruit farmers and other fruit growers – large numbers breed during the latter part of the fruit growing season. We also want to know where else we can find SWD and when during the year – in our gardens? Cities? Fields and woods?

What to do

We would like you to use a Fruit Fly trap to catch SWD over a week, count what you have caught and enter the results in our iNaturalist project online!

  • You can either buy a commercial trap
  • OR make your own from some simple ingredients!

You will need:

⮚ A large empty clear plastic bottle
⮚ Apple cider vinegar (cheapest from supermarket)
⮚ Washing-up liquid
⮚ Some string
⮚ A large nail or auger (2 mm to 3 mm diameter)
⮚ Open the empty plastic bottle
⮚ CAREFULLY pierce 8 holes in the bottle more than half way up the bottle.

Adults – please supervise children for this step. To avoid injury, I recommend doing this on a table or a board, lie the bottle down, hold it firmly at the bottom half and gently pierce with a sharp metal point or augur down, through the upper side of the bottle towards the board.

(If the point slips, it should go safely into the table or board and NOT into your hand.)

The holes need to be 2 mm to 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.

⮚ Fill the upright bottle to ¼ to ⅓ with apple cider vinegar. The level must be below the holes!
⮚ Add one or two drops of washing-up liquid
⮚ Screw lid back onto plastic bottle
⮚ Use the string to hang your baited trap from a tree/bush/holder at a suitable place.

Leave the trap for one week.

⮚ At the end of the week, seal up holes with sellotape.
⮚ Swirl bottle gently and carefully pour the fly catch into a white /light coloured plastic dish.
⮚ OPTIONAL – I strain the fly catch through an old metal tea sieve and then transfer the flies to clean water. with a bit of vinegar and alcohol in it to preserve them.


Identification help

⮚ Either use a magnifying glass or a low power microscope to magnify the catch.
⮚ You can also take a close-up picture with a smartphone or camera on macro setting and then magnify the catch by zooming in on the picture on a PC or tablet screen. I’d love to see your pictures too, so add them to any observation.
⮚ Fruit flies are very small, between 2 mm and 5 mm long. They are quite distinctive.
⮚ To identify SWD, use the project banner pictures to help you.
⮚ Male SWD are obvious even to the naked eye – they are red eyed fruit flies with a black spot at the end of the wing.
⮚ Female SWD are best viewed under 10× to 30× magnification – where their vicious 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.

To add an entry:

⮚ Go to
⮚ Sign in (or register and then sign in if you are not a member yet)
⮚ Click on Add Observations

Information you will have collected or available to enter to your observation

⮚ Count of

  • Number of male spotted wing drosophila
  • Number of female spotted wing drosophila (microscope users only)
  • Total of ALL Fruit Flies seen/trapped, INCLUDING Spotted Wing Drosophila
  • All six legged minibeasts (insects), including ALL Fruit Flies
  • Minibeasts that are not insects

⮚ Also tell us

  • What you have caught – use a single name like spotted wing drosophila or Common fruit fly, or Nothing (we are limited by the iNaturalist setup – it requires a name of something)
  • Date you harvested the trap (date field)
  • Your trap location (map field)
  • Whether there was fruit near the trap (choose from drop down list)
  • Whether your trap was in a garden or somewhere else (choose from drop down list)
  • If there was ripening fruit nearby? (choose from drop down list)
  • If you tried to control fruit fly with sprays etc. (choose from drop down list)

Discarding waste at the end of the experiment

Bleach and flush away the flies and used trap liquid, and wash your hands.


⮚ Record ALL results – even if you did not catch anything.
⮚ (You can enter Nothing as an observation name in the first box ‘What did you see?’ if you did not catch anything).
⮚ If I see no Spotted Wing Drosophila, but fruit flies are present, I enter ‘Common Fruit Fly’

Your results will be valuable.

⮚ You can try different locations and different times of the year.
⮚ Fruit farmers will be particularly looking for fruit flies and damage when fruit begins to ripen.

Have you got this far!?! Great! Go out and make a trap and I’ll look forward to your results in a week.

The results will be accessible for all.

What else can you do with this project?

You can download the data collected so far and do your own comparisons and analysis. If you do – tell us and others about it.

Terms and Conditions of the project

This is an open science project, for anyone to participate and to see the results. We encourage individuals of any age and profession, groups, schools, farmers and researchers to take part and also to analyse the data.

The following six terms apply:

  1. Compliance with iNaturalist Terms and Conditions.
  2. Non-commercial use only.
  3. Use of data:
    You are free to use and interpret the data in this project on condition that you acknowledge its source as “iNaturalist project, Quekett Spotted Wing Drosophila Survey Experiment”.
  4. Images and journals submitted to this project remain the copyright of the person/group that submitted them. Permission to use other peoples images and journals must be sought from the copyright holder.
  5. You grant the Quekett Microscopical Club a world-wide, royalty-free, and non-exclusive license to reproduce, modify, adapt and publish Your Content submitted for this project. This is solely for the purpose of our (The Quekett Microscopical Club) displaying, distributing and promoting Your observations and journal as part of any analysis, reports or publication using entries to this project.
  6. You accept that other researchers can use the LOCATION and DATA ENTERED IN THE OBSERVATION FIELDS for non-commercial research and interpretation.
    (If concerned about LOCATION information being more widely available, use the ‘Change Geoprivacy’ option ‘Obscured’ (below map) after entering your location, which places a random marker in a 10km radius from your entered location OR change geoprivacy to ‘Private’, where only the project curators will see it).

I’m Chris Thomas, a member of the Quekett Microscopical Club. We are promoting this survey because it is a simple, very practical and relevant use of microscopy, open to all.

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