Instructions for collecting Drosophilid flies:

The following materials are needed:

•Fruit bait (banana peels are best)

•6 to 8 empty plastic drink bottles (around 1 liter size works well)

•String, tape, scissors

•Plastic vials from Applied Scientific and cotton balls large enough to plug them

•Instant fly food from Carolina Biological and baker’s yeast

•Flynap anesthetic (in small tube labeled with “F”) and gloves

•Small paintbrushes

•Magnification device

Preparing and setting out the traps:

•Slice one window in each bottle by making three cuts, about 5 centimeters each, on the sides and bottom of a square (see diagram below). Fold the window outwards.

•Get some fruit to use as bait. One or two banana peels per plastic bottle is enough.

•These flies are attracted to rotting fruit, so you could set traps indoors (e.g. kitchen) or outdoors if it’s not too cold outside for the flies (e.g. near dumpster). Traps can be hung with string or set upright on a ledge, for example.

•When you’re ready to set a trap, add some bait (such as 1 or 2 banana peels) to one of the plastic bottles. Sprinkle a small amount of yeast on top of the bait (you’ll need to save most of the yeast for later, so don’t use too much in the traps).

•Cut some string and hang the trap in a shady place (or set it upright in a shady place).

•Repeat this process for the rest of the traps. You should have 6 to 8 traps in the same town or village.

Before you go to collect the traps:

•Traps should be left in place between 2 to 5 days.

•The day before you collect the traps, you should add water to the instant fly food in the small plastic tubes. Add 10ml of instant fly food to the tube, then 10 ml of water. Let it soak in overnight, and then pour off any excess water. Keep the tubes covered with cotton whenever possible.

Collecting the traps:

•Take down one of the traps (which should now have some little flies inside it) and push the plastic window closed. Tape the window shut so that all the cracks are covered and the window will remain securely closed. Put the trap in your bag.

•Once you have taken down and taped shut all of the traps, you can transport them back to your home base. Take care to keep the traps out of the sun while you travel, because extreme temperatures will kill the flies you’ve collected.

What to do with collected flies:

•Wash your hands before these steps to prevent contamination.

•Remove cotton balls from 10 plastic vials at a time. Then add just a few particles of yeast to each vial (even just 5 of the tiny pellets are enough). Do this for each of the vials.

•Now you can anesthetize some flies. Flynap is a product that makes the flies unconscious for several hours. It’s safe enough that it’s used by schoolchildren, but it’s best to avoid contact with skin (you can use lab gloves) and to use it in a ventilated area. Dip the plastic wand into the Flynap. Let it soak for a few seconds, then remove it and re-cap the tube. Place a trap with collected flies on its side. Remove the cap from the bottle and insert the Flynap-soaked wand. Rub the Flynap onto the inside of the bottle, then remove the wand and replace the cap. It may take several minutes for the flies to become unconscious, because the trap has a fairly large volume of air for the Flynap to diffuse into. Repeat the above process to put some Flynap inside each trap. If necessary, you can repeat the process to add a second dose of Flynap.

•Once the flies inside a trap have been unconscious (not moving) for at least a few minutes, you can cut open the trap. I suggest cutting all the way around the middle of the bottle. After that, you can easily empty out flies from the top half of the bottle onto a well-lit working surface. For the bottom half, take out the fruit bait and use the paintbrush to remove flies from the bait. Then, empty out any other flies from the bottom half of the trap.

•Take each fly and put it in a separate tube. If you know what to look for, you can select for a particular species or for female flies (which are likely to produce offspring inside the tube). Below are some pictures of Drosophila melanogaster.


FEMALE Drosophila melanogaster


The female has a larger, striped abdomen.

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MALE Drosophila melanogaster

The male has a smaller abdomen with a darker end.

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