Some hydroponic gardeners need help with pollinating their crops whether they garden indoors or outdoors. But pollination can be especially difficult in indoor gardens located in greenhouses or basements, because there are no bees available to help pollinate their plants. And depending on the type of plant, or the number of plants, hand pollinating can be a difficult as well. A recent development has been the use of “Blue Bottle Flies” to pollinate crops instead of bees.
Blue Bottle Flies are from the Blow Fly family. They are larger than regular house flies and grow to about one half inch long. Their head and thorax (front and middle sections) are gray and the abdomen (large rear section) is bright metallic blue. They have red eyes and clear wings. Flies don’t intentionally pollinate flowers; they just accidentally do it while they are flying from flower to flower looking for good resting spots.
According to the North Central Regional Plant Introduction Station (NCRPIS) where they have been experimenting with using flies and other insects as pollinators, “In cages, these lazy flies are particularly good at partnering with honey bees to pollinate carrots and other plants in the carrot family. Two kinds of flies—blue bottle flies (Calliphora sp.) and house flies (Musca domestica) – have been put to work at NCRPIS.” They also go on to say “Blue bottle flies last longer in the cages, but more complete pollination occurs when both species are present.”
Like other flies, the Blue Bottle fly is a meat eater and feeds from dead animals. They even feed on living animals with open wounds, animal manure and other decaying matter. The Blue Bottle fly also loves the nectar of flowers. So they wind up pollinating the flowers unintentionally as they are looking for something sweet to drink. Bees, on the other hand, intentionally search out flowers to harvest nectar, and then take it back to their hive. As an added benefit flies work at cooler temperatures than bees, so they are even more beneficial in cooler climates and to cool weather crops.
Even though the Blue Bottle fly may earn their keep, they are still flies and can be irritating to people, even though they will not sting you. As a result flies should not be used to help pollinate in an indoor garden in a house or near doors and windows where they could easily get into the home.
The fly’s work best in caged area’s like greenhouses because they are basically trapped. Once a fly leaves the area it does not generally return like bees will. The nectar in the flowers is a food source to bees, so they keep coming back looking for the food. For fly’s, meat is the food source, and the sweet nectar is just a nice extra if it happens to be in the area. Typically the more pungent or bad smelling something is, the more fly’s (Blue Bottle fly included) are attracted to it.
Flies are attracted to meat and you can encourage them to stick around an area by leaving some in the open where they can easily find it. Fresh meat works better than decomposing meat. Because fish tends to have a stronger odor, it usually attracts them best. They will also lay their eggs directly on the meat, producing another batch of flies to pollinate your flowers and vegetables at a later date.
Compared to bees, flies have a much shorter life span, and are considered to be a short-term pollinator. They will need to be replaced often if you are pollinating continually flowering plants, like peppers or strawberries.
Even though fly’s have a short life span of typically 7 to 30 days depending on environment, you can breed them rather than buying more all the time. After mating, the female Blue Bottle fly lays her eggs in the same place where she feeds (on dead animal flesh, fresh meat, animals open wounds, manure etc.). The eggs hatch quickly and the young larvae, called maggots, begin eating immediately. The maggots are whitish in color, with small black hooks that they use to tear flesh. After a week or so of feeding, the larvae (maggots) crawl away to a dry place and burrow into the soil and become pupae (resting stage). The pupae are tough brown cocoons.
This pupae is what you receive when you purchase flies from a vendor. The flies are in a hibernating/dormant stage at this point, and can be stored up to 3 months in refrigeration. After taking them out of refrigeration, adult Blue Bottle Flies come out of the pupae in about two or three weeks. They will breed often during the warm months, and both larvae and pupae can live through the winter, but adults die when it gets too cold. They will become active again when temperatures rise above 50 degrees during the day.
Jeff Sanders runs a hydroponics website call HomeHydroSystems.com to help hydroponics enthusiasts learn how to build their own hydroponic systems, as well as learn about many topics related to hydroponics so they can grow to their own crops successfully. He is a hydroponic gardener and enthusiast with over 7 years of experience and is currently building a small commercial hydroponic greenhouse to grow fresh herbs. You can contact him at firstname.lastname@example.org.