Flies as a food source

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Flies as a food source

Postby prussell » Mon Apr 22, 2013 2:16 pm

I endeavour to feed my fish a varied diet that includes live food such as daphnia and blood worms. Flies are also a natural food source for many species of fish so I wanted to include them as part of the feeding regime. It was obviously that it would be impracticable to catch flies individually. It would be a simple matter to obtain larvae from an angling shop of either bluebottles (caliphoria vomitoria) or the housefly (musca domestica) and set them aside to develop into the adult stage but these flies would be too large for many of the species commonly kept by hobbyists. I remembered using flies called drosophila whist at college as part of a genetics study. Drosophila is a genus of small flies belonging to the family Drosophilae. Most people will know them as ‘fruit flies’ or ‘wine flies’. There are numerous species within this genus; they are mostly between 2-3 mm long and easy to cultivate throughout the summer. The only equipment and materials required to culture them are jam jars, a translucent plastic funnel with a diameter of approximately 10 cm, a small bottle with a narrow neck that will fit snugly to the taper of the funnel, rubber bands, paper kitchen towel a knitting needle, an old sock, banana and dried yeast that can be purchased from the home baking section of most large supermarkets.
Put approximately 5cm of very ripe banana with the peel into a jam jar. Add a very small pinch of dried yeast granules and mash them together with a fork. Place the jar outdoors in an area that is shaded. Lay the jar on its side in case it rains and keep it raised off the ground or else it will fill with slugs and ants. The mixture will soon start to ferment and attract drosophila. The flies will feed and lay eggs so that their offspring can exploit the food source. Each female will lay about 400 eggs in her lifetime but usually only lays a batch of about five or six eggs in any one location. Expose the jar for two days; during this time it will probably have been visited by dozens of adult flies. Cover the jar with a piece of paper towel and secure it with a rubber band. Set the jar aside in a place that is dry and out of direct sunlight and wait for the completion of the lifecycle from eggs through larvae, pupae to adults.
The time from egg to adult fly is temperature dependant and therefore very variable. Typically, one can expect to find a jar full of flies after 20-35 days. Once the adults have emerged from the pupae, the flies can be left in the jar for several days until required. Transferring the flies to the aquarium is quite simple but it is a task best started outdoors in case there are escapees. Place the funnel upside-down over the top of the jar. Push the knitting needle down the funnel and cut open the paper towel with a circular motion. Quickly place the inverted bottle over the funnel’s spout. I find that the empty bottle of a well-known liquid coffee essence is ideal. Cut the foot off the sock and use the ankle part of the sock to cover the jar and rim of the funnel. This keeps the funnel in place and encourages the flies to migrate out of the jar, through the funnel into the bottle as they are attracted to light. Occasional taps on the side of the jar with a coin will keep the occupants in flight and hasten their progression into the bottle. Within a few minutes, the majority of the flies will be safely entrapped in the bottle. The bottle can now be turned up the correct way with the funnel still in the bottle. A small quantity of water should be poured into the bottle. Hold the funnel in place and shake the bottle until the flies are drenched and no longer able to fly. The bottle can now be taken indoors and poured into the aquarium without any risk of filling your home with flies.
The flies are taken with relish from off the surface with a burst of speed and it is pleasing to observe the fish feeding as they would the wild. The numbers of flies obtained per batch can be anything from 10-150 and it is dependent on the time of year and the weather when the jars were set. I sometime collect two crops of flies from one jar by quickly placing the funnel over the jar and trapping the adults that have attracted to the fermenting fruit before setting the jar aside for the eggs to develop. Setting up a jar every few days will ensure a regular supply of live food all summer long and without the risk of introducing disease.
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