Can I make my own substrate to keep fruit flies alive?

Question

I've found that fruit flies make a good staple food for my Red Devil Crabs, but it's expensive to keep buying a new batch of them every time the substrate starts to mold. Is there a way I can make my own substrate for them?

Answer 1

It's incredibly simple to culture fruit flies. Here's a list of what you'll need for a pretty "bread and butter" recipe:

1. An empty container (I use peanut butter jars).
2. Instant Potato Mix.
3. Powdered Milk.
4. Sugar (I use regular, some people use powdered).
5. Baker's Yeast.

Mix together the following ingredients with equal parts water:

4 parts of the potato mix, 
2 parts of the powdered milk, 
and 1 part sugar.

Line the bottom of the container with the mixture and sprinkle in a pinch of the yeast. It will seem a little mushy at first, but the potato mix will soak up the water after a minute.

The final thing you'll want to do is make sure the fruit flies have a way of climbing up off of the substrate to lay eggs (they won't lay eggs in it). I use a shredded-up paper towel, but you can stick in popsicle sticks or use straw/hay; just about anything since they're so small and light.

As far as maintaining the cultures, you should be able to notice when the substrate starts to mold after a few weeks (as the substrate is white, and the mold is black). I would say the substrate lasts 5-6 weeks, after which you should transfer any flies leftover to a new container or use them for feeding.

The flies will grow exponentially, so you can start a new culture each week or so, until you are comfortable with the amount of flies being produced.