About Fruit flies
Fruit fly make an excellent live-food choice for various captive animals, including ants.
They are widely available from online shops as feeder insects for small reptiles and amphibians as well as from speciality pet stores.
There are two species typically available to you; Drosophila melanogaster and Drosophila hydei. Drosophila hydei has larger adult flies which are approximately 3mm in length. Drosophila melanogaster adults reach only 1.5mm and typically make a better choice for ant keepers.
Drosophila melanogaster fruit flies take only two weeks to complete their life-cycle; from egg to maggot to adult fly, with newly emerged adults being capable of reproduction after only 24 hours. Drosophila hydei is slower to reproduce and takes roughly twice this time to complete its life-cycle.
Drosophila melanogaster fruit flies are available in flightless and wingless mutations. These mutations have been bred into captive cultures and make handling the flies much easier. Flightless fruit flies do have wings, but cannot use them.
Container
Your container needs to be escape proof and well ventilated. A glass jar or plastic cup can be used for small cultures and are more appropriate for keeping smaller numbers of flies for ants. I use plastic cups with kitchen roll over the top held in place with a tight elastic band. This means I can simply throw away spent cultures without the hassle of cleaning and sterilising and without the worry of spreading mould or disease into new cultures.
Following this procedure will produce many more flies than I ever need for hundreds of ants.
Culture Medium
Essentially the medium is the food source for the flies, serving as food for both larvae and adult flies. Specially formulated mediums can be purchased for rearing fruit flies, but I've enjoyed success with the following formula:
1 part white sugar
2 parts powdered milk
4 parts instant mashed potato
I mix this with equal parts water and fill my plastic cup 1/3 full and give it a quick zap in the microwave. I leave the culture for 15 minutes to let it cool and solidify before adding the flies.
To give the adults more space to lay eggs, I sometimes cut up another cup and lie pieces diagonally inside on top of the culture medium. Cotton wool or crumpled paper towel will work just as well.
I add only 15-20 adult flies from a culture that is 15 to 30 days old; yes, this means I start a new culture every 15 to 30 days. Label your cultures with their start date, this way, you will always be able to locate young (and thus healthy) adult flies.
I'm not sure how much of a difference this makes, but for the sake of genetic diversity, I mix adults from multiple cultures into a new start-up culture with every 4th or 5th new culture.
Environment
Keep your cultures at 20 - 26°c, this strikes a balance between efficent reproduction speed and slowing down the growth of mould.
Humidity should be kept high enough that the medium does not dry out (above 65%). But not excessively so, as this will encourage mould.
If you have room, keep your cultures apart, don't allow old cultures to rest against new ones.
Feeding off your flies
If I foresee the need for more flies further down the line, I will simply start more cultures. If you have the capacity, it is always wise to have have multiple cultures on the go at once, and better still, if you stagger these by a number of days so breeding stock are always available.
There should always be enough adult flies, but I tend to feed off only flies from cultures over 30 days old that won't be used again to start new cultures. I tend to dispose of cultures once they are 45 days old regardless of their state.
If you stay vigilant with these guidelines, you will find that mould, mites etc will never get a chance to establish and pose a threat to your cultures. If you follow my recommendation of disposing of cultures before they are 45 days old and keep multiple cultures going in parallel, you will never find yourself short and will quickly recover from failed cultures when they do happen.
A benefit of having lots of small cultures is, I always have a number of spent cultures at any one time, and as these are approaching their 45 day expiry, I pop them in the freezer for 10 seconds. This slows the flies down and makes it easy to pick out individuals for small ant colonies. At this point, you can either dispose of the culture or if you hate to see it wasted, place it back in the freezer to provide larger colonies with a ready supply of dead fruit flies.
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