Fruit Flies

Posted by in Live Foods

Flightless fruit flies are an easy-to-culture feeder insect for small reptiles and amphibians. They are especially well-suited for dart frogs, reed frogs, mantella frogssmall geckos, and baby chameleons. They can be purchased from the occasional pet store but are more easily found for sale online from reptile and amphibian supply companies.

Types of Fruit Fly

The two fruit flies commonly available are Drosophila melanogaster and Drosophila hydei. The main differences between the two species are the adult size of the fly and the time it takes to go through their life cycle. D. hydei is the larger of the two, with adult flies measuring around 1/8 inch (3 mm), while D. melanogaster matures to a smaller size of around 1/16 inch (1.5 mm).

Both species come in flightless mutations where they have wings but are incapable of flying. Instead they hop or flutter around. D. melanogaster is also available completely wingless and this mutation is especially easy to deal with, only able to crawl around and appearing from a distance much like a small ant rather than a fruit fly.

What’s a Culture?

Unlike crickets and other common feeders that are sold individually, fruit flies are sold in cultures that produce flies for a month or more before expiring. A fruit fly culture usually consists of a jar or other container with media in the bottom that feeds fly larvae and sustains the culture.

Life Cycles

Timing is everything when it comes to culturing fruit flies. It is important to setup cultures on a weekly schedule and to plan ahead, taking into consideration each species’ life cycle. D. melanogaster takes roughly two weeks (depending on temperature that cultures are kept at and medium used) to go from egg to larvae to pupae to adult fly and the newly morphed flies can reproduce after 24 hours. D. hydei develops more slowly and takes around three weeks to go through its life cycle. Because D. melanogaster has a faster life cycle most people find it easier to culture than D. hydei.

Container Options

The container that fruit flies are cultured in has to be escape proof but also ventilated. Some people use mason jars, screwing down paper towel or thin fabric over the top to provide ventilation. Another option is plastic 24 oz. or 32 oz. deli containers. Holes can be cut in the lid and fitted with a foam plug. There are also plastic containers designed specifically for housing invertebrates that come with ventilated lids.

Fruit fly containers can be put in the dish washer or rinsed with hot water and reused. There is no need to throw containers away after one use.

What Do Fruit Flies Eat?

Fruit flies and their larvae feed on the bacteria and yeasts of decaying fruits and vegetables. As such, a successful culture will not only culture flies but also breakdown in a controlled way as to culture plenty of fruit fly and larvae food.

This starts with a medium to culture flies on. Fruit fly media can be purchased from biological supply and pet supply companies, or you can make your own. You can use most any fresh fruit and vegetable (bananas are popular) but the most convenient options start with dry ingredients that are then re-hydrated. These media come in a powder that water (or other liquid) is then added to.

Fruit fly media in a container with yeast

Fruit fly media in a cup with yeast added

No matter what media you use, you will have to add baker’s yeast to it once it sets. The yeast helps start fermentation and gives the flies and their larvae something to eat. Only add yeast once the media has cooled (if using hot water or cooking it) and only add it in moderation. Usually 20 granules per culture is plenty. Alternatively, some people activate the yeast first as you might before baking. In this case a small spoonful of yeast is mixed in a little lukewarm water along with sugar, allowed to sit for 5-10 minutes until it starts foaming, and then a spoonful of the liquid can be poured over the media in each culture.

Once the media has set and yeast has been added you can add flies, the more the better. Adding 25 flies should usually be enough to get one culture going but adding 100 flies will do the job better.

The Right Temperature

Keep fruit fly cultures in an area where the temperature does not fall below 70°F (21°C) or rise above 85°F (29°C). The flies go through their life stages faster when kept at higher temperatures and slower when kept at lower temperatures.

Surface Area and Fly Production

Fruit fly culture with rolled coffee filters to increase surface area

Fruit fly culture with rolled coffee filters to increase surface area

You can increase the amount of flies produced by adding extra egg-laying sites to the culture. Fruit flies will lay their eggs on pretty much anything solid. You can sink pieces of cardboard, poster board, or aluminum window screening into the medium to form extra solid egg-laying areas. Excelsior, commonly sold as American moss or wood wool at craft stores, works very well for creating additional egg-laying sites and is popular.

Homemade Media Recipes

Making your own media from scratch saves money, especially when culturing large amounts of flies. There are numerous homemade fruit fly media recipes. Below are two recipes for homemade media I have used with success. Consider modifying and experimenting with them to suite your needs.

The “Harvey Peterson”

  • 1 part white sugar
  • 2 parts powdered milk
  • 4 parts instant mashed potatoes

Combine dry ingredients together, and then mix with equal parts water in a culturing container. For D. melanogaster 1/2 cup of medium with 1/2 cup of water seems to work well in 32 oz. containers. Use more for D. hydei.

The “Power Mix”

In three separate containers…

Boil:

  • 1 mashed banana
  • ½ can of grape juice concentrate
  • 14 oz. of applesauce (half of a large jar)
  • 1/8 cup of molasses

Combine:

  • 1 cup of instant mashed potatoes
  • ½ cup of brewer’s yeast

Pour together:

  • 1 cup of water
  • 1 cup of vinegar

Once the boiled mix has cooled to a reasonable temperature add 6 tablespoons of it to a 24 oz. or 32 oz. container. Then add 6 tablespoons of the dry mix and then 2-4 tablespoons of the water/vinegar mix and stir well. The amount of water/vinegar mix that is added will depend on the humidity where the cultures are kept and how ventilated the containers are. Let it all sit for a few minutes until it solidifies.

Some additional tips:

  • Do not mix different strains of fruit flies in one culture or allow native flying fruit flies into a culture. You will end up with a face full of flying fruit flies when you open the culture the next time if you do.
  • Setup cultures weekly even if you do not need the flies. It is better to have too many flies than not enough. Pick a day, say Saturday, and that is fruit fly culture day no matter what and you will never run out.
  • Only use flies from healthy cultures that have just recently started producing to make new cultures, and discard cultures that are over 4-6 weeks of age to avoid issues with mites or mold.
  • Work from newly setup fresh cultures to older cultures last when feeding. This will also help avoid spreading mites or mold.
  • If mold is noticed in a culture, throw the culture out. Do not try to salvage it. Mold is a common problem and spreads easily if not contained.
  • Write the date that you setup a culture on the cup to keep track of when you should start new cultures and dispose of old ones.
  • Reuse your culturing containers, which can be put in the dishwasher or soaked in the sink with hot water to clean them.