Fruit Flies – Drosophila melanogaster
We all know that live food on at least an occasional basis is one of the best things we can do to foster good health, good growth, and regular spawning in our killifish. But what live foods can we feed during the “off” seasons, when mosquito larvae aren’t available, and the daphnia cultures have gone dormant?
A regular standby of many aquarists is fruitflies. Most killifish will gladly accept them, as will many amphibians and reptiles.
“You’re raising WHAT in the house?”
If your spouse asks this, keep in mind that she or he has a legitimate concern. Ask anyone who has ever been plagued by a cloud of them around softening fruit. However, a larger, wingless strain of cultured fruit fly is now available which not only cannot fly, but is more prolificand will breed true unless contaminated by wild stock.
Sometimes this information alone is enough to overcome spousal resistance.
Containers for culturing fruit flies should be large enough to contain sufficient culture medium, but not too large to handle easily. Glass containers iced tea or juice bottles, or suitably sized canning jars are a good choice, and can be easily run through the dishwasher between uses. Plastic containers (2 liter soft drink bottles with the tops cut off, or juice/iced tea bottles) also work well, and can simply be recycled or thrown away when they have served their purpose.
Growth medium for fruit flies is a matter of preference. Fresh, decaying fruit or fruit based mixes will work, but tend to be smelly, messy, subject to mold and to attracting unwanted insects.
Commercially available cultures are easier to use and considerably neater to work with. The fruit fly medium from Carolina Biologicals is recommended by many. According to Barry Cooper, “You put a scoopful in the bottle, add an equal volume of water, wait a minute, add a sprinkle of yeast, then add the fly innoculum. Very easy.”
Alternatively, try using instant mashed potatoes. Several variations of the recipe are available, but all begin by preparing instant mashed potatoes according to label directions. Then:
1) add some sugar, a drop of blue food coloring (if you like), and some yeast. Sprinkling the yeast on top works better than mixing it in, which usually results in the culture “rising”; this can get messy. The result of this recipe is very similar to the culture medium sold by Carolina Biologicals, at a fraction of the expense.
2) add one tablespoon of sugar per cup of medium (brown sugar or cane syrup will also work) and a pinch of salt.
3) to the basic mixture you can also add flour, producing a “doughier” consistency. This can then be frozen into appropriately sized portions for later use.
For an entirely different recipe, try this one suggested by Art Abramovitch: add yeast to a quantity of beer; wait half an hour or so, then add dry baby food oatmeal to a consistency that is moist but not sticky.
Spoon your culture medium approximately one inch deep into containers and add a “scaffolding” for the flies to crawl on. Plastic fly screen from the hardware store, cut into strips, works well, as do popsicle sticks or crumpled paper.
Add fly culture innoculant, then cover the container using a piece of fine mesh cloth or old nylon stocking held in place with a rubber band; or a “plug” of cotton or plastic foam.
Feeding Fruit Flies
When preparing to dispense the adult flies, first rap on the side of the culture container once or twice to knock the flies to the bottom. Remove the cover, then GENTLY shake the flies out. Immediately recover the container, and be certain to cover the tank you’re feeding as well, to avoid escapees.
Known problems
The potato culture medium can get messy if bacteria cultures take hold before the yeast. To avoid this, try dissolving the yeast in aged dechorinated tap water, then add the instant mashed potatoes and the yeast on top. Let sit for a couple of days, then add the flies.
The culture also may develop mold. If the culture medium is too dry, mold is inhibited, but it may be difficult to remove the flies for feeding.
Fly Larvae an untapped food source?
We don’t usually think of “maggots” in positive terms, but fruit fly larvae are as good a live food as their mature, adult relatives. This concept can be taken a step further, if you are adventuresome and willing to give it a try.
Ramon De La Cuetara of Puerto Rico suggests setting up outdoor fly cultures, using covered pint plastic containers with half inch holes cut in the lids. A culture medium of 1/2 teaspoon mashed potato powder and 1 tablespoon water is put into each container, and the container then set outside for about a week.
To harvest the larvae (Ramon says he gets mostly fruit flies, but sometimes housefly larvae as well), fill the container with water, stir the medium to dissolve it, then pour through a brine shrimp net. Wash in clear water, then feed as a free source of nutritious live food.
— GCKA Newsletter, December 1997