Drosophila as Feeders

Flightless Drosophila fruit flies are common feeders for small insectivorous pets, such as dart frogs (Dendrobatidae). They are also essential for raising many species of mantids in any sort of quantity. Two species within the genus Drosophila are often used as feeder insects: D. melanogaster and D. hydei. The main difference is size. D. melanogaster is slightly over 1/16th of an inch, but D. hydei are about 1/8th of an inch. Both are popular feeders and are sold by some of the vendors in the links section. There are other feeders that are the proper size, but they are more cumbersome to raise. The other feeders are impractical to breed in large quantities, whereas fruit flies are easy to breed. I only know of a few published recipes for raising these as pet food. Most people seem to choose to purchase media mixes from major fruit fly suppliers. I think many people would prefer to make their own media if they had a recipe. I have a recipe that works well. It is not quite as productive as the commercial mixes, but I find that it tends to produce a steadier supply of flies over a longer period of time. I have had cultures last for two months and constantly have hundreds of flies.

The cups used to culture flies are important. I use the vented lids from Josh’s Frogs in combination with 32oz deli cups. Unfortunately, Josh’s Frogs recently modified their vented lids. The new lids have thicker plastic and their logo, but the holes are slightly larger. The hole size is not a problem when keeping most insects in the cups, but the larger holes allow other types of flies into the fruit fly cultures. These other flies can wreak havoc on the culture by out-competing the fruit flies. Unlike the fruit flies, which are flightless, these invaders fly and are extremely annoying. To prevent other flies from invading the culture, I have put fabric lids on top of the vented lids. The vented lids provide the proper amount of ventilation and are easier to clean than the fabric lids (flies make a mess of their culture). The fabric lids keep the pests away. It is annoying to have to use two lids and makes the enclosures harder to stack, but at least there are no invading flies. I have shared my observations with the Josh’s Frog’s staff, so hopefully, the old lids will become available again. I would like to have both available because, while the new lids are bad for fly cultures, they are great for other pet invertebrates. The thicker design of the new lids makes it harder for beetle grubs and other strong-jawed pets to chew their way out.

Here is the recipe for fruit fly media:

  • 500 ml beer
  • 200g Mashed Potato Powder

Mix together until smooth

  • 100 ml White Vinegar

Mix again, and add water or potato power to perfect the consistency. It should be like a soft paste.

  • 1 tsp Active Dry Yeast
  • 3 tsp Methyl Paraben

Mix thoroughly and put into fly cups or refrigerate as one large batch.

This media works for either the D. melanogaster or D. hydei. The only ingredient that is not readily available (for most people) is methyl paraben. Its role is a mold inhibitor, and Josh’s Frogs sells it here. They sell it by the pound, which is sufficient for many dozens of cultures. The vinegar is also a mold inhibitor, but the methyl paraben makes a huge difference. This media can also take additives. For example, since I raise mantids with my flies, I often add bee pollen as it is rumored to be beneficial when incorporated into a mantis’s diet.

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