Flightless Fruit Fly, Drosophila hydei. Of the two commonly available species of non-flying fruit fly,
this is the largest. Photo ©2010 John P. Clare / FrogForum.net
Culturing Drosophila fruit flies can seem daunting to the newcomer, usually because people tend to think it will be smelly, messy, dirty, or just difficult. Done correctly, it's quick, easy, relatively clean and a low cost way of providing quality live food for your frogs. Many frog enthusiasts first think of fruit flies for feeding poison dart frogs, but they are invaluable for raising young frogs of all kinds.
Drosophila is a genus of small flies belonging to the family Drosophilidae, whose members are referred to as "fruit flies" or more appropriately pomace flies, vinegar flies, or wine flies, because many species tend to linger around overripe or rotting fruit. They should not be confused with Tephritidae, a related family, which includes the Mediterranean Fruit Fly and are considered pests because they feed on unripe or ripe fruit.
In case it isn't clear, the fruit flies we culture are not the wild fruit flies we sometimes encounter as unwelcome guests in our homes. They are genetic mutants, meaning they possess genetic differences when compared to the wild type flies of their species. These genetic differences render them flightless, and the variations on this include true flightless (they have full wings but can't use them), gliding (they have full wings but can't use them beyond gliding short distances), wingless/apterous (they have no wings, making them look a lot like ants), or vestigial (their wings are malformed and unusable).
Starter cultures of flies can be obtained from online vendors such as Josh's Frogs, biological supply houses like Carolina Biological (who actually discovered the flightless mutant of D. hydei), and many pet shops and chain pet stores such as Petco. Aside from the flies, the primary requirement is a culture medium (plural: media), which usually can be purchased from the aforementioned suppliers, or if you’re feeling adventurous, you can even make your own. In fact, later in this article we will discuss making your own media, along with some recipes and recommended ingredients for your own recipe. We will show you how both authors set up our cultures and the media we use so you can see that these are completely different methods that are equally successful. There are almost as many ways to culture fruit flies as there are people who culture them!
Species and Mutants
The two species of fruit flies most commonly cultured are Dropsophila hydei (the larger of the two), and Dropsophila melanogaster (smaller but quicker to mature). Both are dipterid flies, order Diptera, meaning two-winged. Two-winged flies evolved from four-winged flies but the two hind wings have become "balancers" that aid the flies maneuvers during flight (a balancers is visible in the first photo of this article as a small yellowish colored mass above the middle leg). Both species are sold in more than one mutant, which are detailed in the table below. The main differences between the two species are that Dropsophila hydei are significantly larger flies, take about twice as long to mature, become sterile at lower high temperatures than D. melanogaster, and D. hydei is trickier to culture, having a tendency to crash more often and producing staggered sex ratios. If you culture both species, raise them separately, and you should not mix species in one culture, nor should you mix mutants - mixing mutants of D. melanogaster will produce flying flies!
D. hydei was described to science in 1921 by Sturtevant. It is found wild in the more southerly areas of the USA. D. melanogaster is found wild in most of the world, so don't leave the lids off your cultures for long, or leave gaps/holes in the container, because wild D. melanogaster can turn all of your non-flying flies into flying annoyances in a few generations. This is because the mutations that cause the lack of flight in our captive cultured flies are caused by genetic traits that take a back seat to the flying genes of wild flies (recessive versus dominant genetics).
| Fly Species ||Mutant/Type ||Advantages ||Disadvantages ||Reproduction Speed ||Notes |
|D. hydei||Flightless||- Large Fly, more suitable for larger frogs||- Reproduces Slowly |
- Becomes sterile at lower temperatures than D. melanogaster
- Crashes more easily
- Trickier to start new cultures because flies emerge in different sex ratios
|Slow||Ideal for larger froglets and adult dart frogs|
|D. hydei||"Blond" Flightless||Same||Same||Same||Same|
|D. melanogaster||Flightless||- Small fly, more suitable for smaller frogs |
- Fast breeder
|D. melanogaster||Apterous/Wingless||- Small fly, more suitable for smaller frogs |
- Fast breeder
- Easier mouthful for small frogs due to the lack of wings
|D. melanogaster||Gliding||- Small fly, more suitable for smaller frogs |
- Very fast breeder
- Gliding behavior induces better feeding response in frogs
|- Escapes frequently during feeding preparation||Very Fast||Some people swear by this mutant but they can be more trouble than they are worth if you have a housemate or spouse who doesn't like escaped flies|
|D. melanogaster||Vestigial||- Small fly, more suitable for smaller frogs |
- Very fast breeder
|- If kept too warm, this mutant can develop working wings||Very Fast||Avoid if you can't keep the cultures below about 81 °F (27.5 °C)|
Conditions and Considerations
Before you culture flies, decide where you will raise them. These two species both do well at temperatures from 70-80 °F (21-27 °C). Warmer temperatures lead to increased production in both species, though D. hydei seem to do better at slightly cooler temperatures than D. melanogaster. In practice, most people culture the two cultures at the same temperature for convenience. Warmer temperatures also lead to increased evaporation of moisture from cultures, and this can cause cultures to crash. More on moisture and humidity later. Temperatures above about 85 °F (29 °C) can cause your flies to become sterile, meaning they won't be able to reproduce any more. Sterile flies don't carry a sign saying they are sterile, so by the time you discover it, you may be unable to have producing cultures when you need them. Conversely, temperatures below about 65 °F (18 °C) result in decreased production, though lower temperatures usually will not kill the flies or do them any lasting harm, provided they are not kept near freezing.
The vestigial winged mutant of D. melanogaster, perhaps the most popular mutant, can become flighted at temperatures above about 81 ° (27.5 °). This is because there is a malformation in a protein used for wing development, caused by their genetic mutation, and the warmer temperatures allow this malformation to be corrected. However, these flighted variants are still genetically "vestigial", and if they are allowed to reproduce at normal temperatures, they will produce the original vestigial flies.
Keep in mind that high shelves in a room are going to be a degree or two warmer than lower shelves, because warm rises and cool air falls.
Humidity and moisture are related factors to take into consideration. In less humid environments, it often helps to slightly increase the amount of water used beyond that recommended by a recipe in order to have good humidity in the culture after a week or so while larvae are growing. D. melanogaster are more forgiving of unfavorable moisture conditions.
Finally, before we get into culturing methodology, mites are a common problem when culturing fruit flies. These mites are almost invisible to the naked eye, and are often present in low numbers, especially if you keep your cultures near your frog terrariums, which are natural mite habitats. However, mite numbers in cultures can rise to the extent that they can cause cultures to crash, reduce the productive life of a culture, and reduce the yield of flies. To reduce the chances of mites being a problem, we recommend that you use an anti-mite paper, usually sold in rolls. Place a sheet on your culturing shelf and place the cultures on top of it. It will prevent the spread of mites.
At the temperatures mentioned, D. melanogaster cultures should start producing after day 10. For D. hydei it takes 20-23 days. Discard cultures after about day 30, or at least move older cultures to a different area because mites tend to become a problem the longer the cultures are left.
Regardless of the species and mutant that you choose, or the media that you use, there are items that you need that are the same for both. Here we explain two approaches that work for us and should work for you as well. There are no absolute rights and wrongs in culturing, and you will likely develop your own variation on these methods after you have gotten some experience under your belt.
You will need containers in which to keep the cultures. John uses 32 oz (946 mL) plastic culture cups. Paul uses 16 oz (473 mL) glass jars.
Add which ever medium you are using - the recommended amount (or at least the proportions of medium to liquid if it is a dry medium) should be stated in the recipe. If you had to add hot or warm water, put the lid on and let the medium return to room temperature before proceeding. Once the medium has set, add a pinch of live or active yeast, sprinkled across the surface of the medium - this will help to keep the growth of undesired fungi and bacteria to a minimum. Black mold is a bad sign and you should probably discard any culture that grows such mold before production begins.
Now is the best time to add your flies. For D. melanogaster, 50-100 flies is recommended. For D. hydei, ensure you add at least 100 flies to the culture because this species is more delicate and less prolific than D. melanogaster, and D. hydei often produce flies in skewed sex ratios, so more flies for a new culture ensures you have a good number of both sexes. Sex skewing in D. hydei is particularly a problem in the first few days of hatching so it's a good idea to use a culture that's a few days old.
Now add a small ball of excelsior - an American baseball is a good size example. Excelsior is shreded aspen fibers and it is available from our sponsors and other sources, such as craft/hobby stores and occasionally from hardware stores. The ball of excelsior provides surface area for the flies to pupate and to walk around on. This helps to reduce overcrowding issues and your cultures should last longer and produce more flies because of this. Some people use inverted coffee filters for the same purpose but these provide less surface area. If you use coffee filters, they will stand up longer in the humid conditions of a fruit fly culture if you use 3 or 4, rather than separating a single thickness. Once your culture is prepared, write the date on it, and if you culture more than one kind of fly, note that on the lid as well. Noting the date will help you to keep different generations apart. Now place the culture on your fruit fly culture shelf. This shelf should be somewhere that is not very brightly lit, but it should not be in a dim area either. Follow the temperature guidelines mentioned earlier in this article.
Here are some pictures of the process.
Cultures about Day 7.
Cultures about 2 weeks old, both using excelsior.
Cultures 3-4 weeks old.
Top shelf of a Dart Frog rack. The fruit fly cultures are on anti-mite paper (the blue material). The 2 cultures on the left are
Drosophila melanogaster and the rest are D. hydei.
There are many recipes for culturing fruit flies to be found on the Internet and in books. Here is a selection.
Northwest Amphibian Rescue's Fruit Fly Medium
by Paul Rust
- 1 x 16 oz glass jars 1 US cup instant potatoes
- 1/2 US cup powdered milk
- 1/4 US cup white sugar
- 30 grains of yeast
- Excelsior or coffee filter
Mix everything together dry except the yeast in a bowl, add 1 cup water and mix. Pour into 16 oz jars until 1/3 full. After about 2 minutes drop in the yeast, when mixture sets up (5 minutes) put in some excelsior or coffee filter and add a vented cap. I drop in about 75 flies from a newly hatched culture.
This mix will make 2 16 oz cultures. I only make enough for 2 jars and then make a new batch if I need more. I do this so if a culture crashes from an error I will not lose everything. In 1 week you should have larvae crawling around and pupating. In 2 weeks they should start emerging and be ready to feed to your frogs. Start new cultures every week and even if one crashes you will still have 2 cultures going strong, I usually have 3 cultures per enclosure of different ages and I feed from the one with the most flies while the others are producing more. If you think that this looks really easy, it is. Cleaning the bowl is a snap if you have cats, they love this stuff.
Frog Forum Medium
by John P. Clare
This is a variation on a popular recipe doing the rounds. In my opinion it's very similar to the commercial medium from our sponsor joshsfrogs.com but it works well for D. melanogaster and D. hydei.
- 6 US cups (1.66 L) Potato Flakes. Used to make mashed potato. I like to pick the kind that has as few added ingredients as possible - usually just potato and some preservatives. The cheaper the better. This is a source of starch and nutrients.
- 2 US cups (474 mL) Brewer's Yeast. This is not the same as baker's yeast. Brewer's yeast is yeast that has been killed and is used in the brewing industry and as a supplement for horses. It is the major source of protein in this recipe.
- 1 US cup (237 mL) Powdered Sugar. This is a very fine powdered sugar used in baking. It's the major source of sugar (there's a surprise).
- 2 tablespoons Ground Cinnamon. This really helps remove any smell from the cultures. It's about 90% effective. I'm sure it adds some nutrients too.
- 2 tablespoons Paprika. Paprika is a source of pigment molecules that may or may not help provide color enhancement to your frogs. The jury is out on how effective it is but it doesn't hurt.
- 3 teaspoons Methyl Paraben. Also known as Tegosept. This is an anti-fungal and bacteriostatic agent (limits the growth of bacteria). It is found naturally in many types of fruit. It is considered practically non-toxic and there have been no reports of any effects on frogs fed with flies cultured on media containing this compound.
You're making a dry mixture that you can keep indefinitely until you need to take portions to make cultures. The key to preparing this medium is to keep from making the mixture into too fine a powder. Measure out the potato flakes, then run them in a blender just enough to reduce them from flakes to particles (not a fine powder). The more powdery they become, the harder it will be to mix with liquid when actually preparing the cultures, and the moisture will not be distributed as evenly as desired. Measure out the other ingredients and add them to the potato grounds. Mix everything together using your hands - putting them in a food processor or blender will lead to the powder problem mentioned earlier. Be aware that you will have a lot of powder in the air as you mix everything, but it's all harmless so not to worry. Once everything is mixed, put it in a ziplock bag or a dry airtight container and put it aside for storage. It will stay good for several months. The amount in this recipe will make enough for 20 cultures.
Preparing an actual culture:
- Put half a US cup (119 mL) of dry medium in a 32 oz (946 mL) container.
- Add 2/3 of a US cup (158 mL) of boiling or very hot water. The medium will set quickly so:
- Stir the mixture with a butter knife, making sure to reach the bottom and around the edges. Don't worry if a little of the wet medium gets up on the sides of the culture container.
- Carefully place the lid on the container (the container will be soft from the hot water).
- Let the culture container return to room temperature. I speed this up by placing the culture in the fridge for 1 hour and then letting it sit on a counter for 30 minutes.
- Remove lid, add a pinch of active/live yeast.
- Prepare a ball of excelsior or several thicknesses of coffee filters.
- Add flies to the culture (see earlier for numbers).
- Add the ball of excelsior and make sure to press it down so that it makes good contact with the medium - don't worry about the flies, you should have more than enough to account for any squished flies.
- Replace lid and place on culturing shelf.
Staten Island Zoo’s Homemade Fruit Fly Medium
by C. Eser
- 3 cups instant potatoes flakes (without butter or other flavor additives).
- 2 teaspoons brewer's yeast.
- Mix above dry ingredients together.
- 4 cups of boiled water.
- 2 teaspoons molasses.
- Mix above wet ingredients together.
- Add dry and liquid contents together and stir.
- Divide the mixture equally into containers (e.g. one liter plastic deli containers or Ball jars).
- Sprinkle top of each mixture with methyl paraben (see previous recipe for more info on it) and brewer’s yeast. Use about one teaspoon per container. For the brewer’s yeast, add approximately 1/2 teaspoon per container. Yield: enough for 6 one liter containers.
Atlanta Botanical Garden's Fruit Fly Culture
by Ron Gagliardo, now with Amphibian Ark
- Dry mix: 28 oz potato flakes
- 3 cups powdered sugar
- 8 oz Brewer’s yeast
By volume, mix 1 part dry mix and 1 part liquid. Sprinkle about 10 grains of baker’s yeast on surface. Rinse sides of container with water and while doing so, wet the baker’s yeast. Wait 2 minutes for initial ethanol release from hydrated yeast to dissipate, then inoculate surface of the mixture with a solid layer of fruit flies.
These sources have all the supplies you need for culturing fruit flies. If your cultures crash you can always order your entire fruit fly supply from Josh's Frogs. This is also a good option if you don't have the space or don't want to deal with making your own cultures. You can also order brewer's yeast and methyl paraben from them.
Feeder insects & supplies - Alpha Pro Breeders
If you have suggestions for other options, such as other suppliers, please let us know.
1. The database on Taxonomy of Drosophilidae.
2. Center of Invasive Species Research, University of California, Riverside.
3. Association of Zoos and Aquariums, Amphibian Husbandry Resource Guide.
4. The Amphibian Steward Network, Procedures and Guidelines V 1.0.
First published on Friday July 30th 2010. Last updated Friday July 30th 2010 - First published version.
Article is ©2010 Paul W. Rust and John P. Clare - FrogForum.net. All rights reserved. This article may not be reproduced or published in part or in whole without written permission from Paul W. Rust and John P. Clare.
Comments, suggestions and criticism welcomed!