Grow Grubs! Farming Black Soldier Fly Larvae
The self-harvesting, antibiotic-excreting, protein-rich larvae of a beneficial insect could be the answer to cutting our dependence on imported animal feed.
Every time a new guest visits our chicken area, they ask about the big orange and purple bin with tubes hanging out the back. “That,” I say proudly, “is our black soldier fly larvarium. Want to see inside?”
They hesitate, and may say no. But for those who are interested, I lift the lid. Our guest’s body stays back, ready to run, while they peer in at the mass of wriggling tan grubs covering partly eaten compost. I point out the brown larvae crawling up ramps in the back of the bin, and describe how these are ready to pupate and looking for light.
Sadly for them, they will crawl out only to be eaten by the waiting chickens.
Whether you find them gross or fascinating, the black soldier fly (Hermetia illucens) may be able to close the loop on one of the weakest links in self-sufficiency here on the islands - the lack of local animal food. The larvae of black soldier fly are very high in fat and protein and are a huge favorite of chickens and pigs. They can also be fed to ducks, other birds, fish (best if dehydrated), and reptiles.
Larvae provide a land-efficient, intensive food source ideally suited for regions with limited farmland for growing grains. In just one square foot of grub bin you can produce35 pounds of protein a year. To get that much protein from soy, you would need one-tenth of an acre. Farming larvae instead of purchasing grain of course saves the cost of imported grain, which can be two to three times higher than on the mainland, plus you haven’t contributed to burning fossil fuels to import grain.
Black soldier fly are different from other flies in several ways that make their larvae the best to raise. Most importantly, they are not a disease vector, because in their short life as adults they do not eat. They don’t even have mouths. When the larvae are ready to pupate (around 2 to 4 weeks after eggs are laid), they secrete their digestive system, lose their mouth, and produce an antibiotic coating. Therefore, unlike house flies, they cannot carry disease between wastes and foods we plan to eat. This also makes them safe to feed to our animals.
Soldier fly larvae are very rich in protein and fat. They contain 34% - 45% protein, 42% fat, 7% fiber, and 5% calcium, which is critical for strong chicken eggs. Research has shown that larvae fed fish waste are higher in omega 3‘s and that this translates to higher omega 3‘s in chicken eggs (described by Olivier, see References).
Larvae can be fed agricultural and slaughterhouse waste, converting a potential pollution problem to a food source. Fish waste, cow pies, and papaya are great larvae foods. The only things they don’t eat are tough and woody items such as avocado pits, coconut husks, and bagasse (sugar cane stalks after being pressed).
We feed our larvae the compost that the chickens don’t eat directly. This season our larvae bin has been getting a lot of rinds from citrus, jackfruit, ulu, and lilikoi, excessive banana peels, and bad avocados. The larvae also find corn cobs and pineapple skins delectable. Coffee grinds help control the aroma.
A picture of three life stages can be found herehttp://blacksoldierflyblog.com/bsf-basics/
So You Want to Be a Larva Farmer
Soldier flies are common in Hawaii and active year-round, so you should be able to attract them easily with some odorous compost. The exception is if you live where it is colder than 75 degrees at the hottest time of day. If you see active bees, then you should have soldier flies.
You can either make your own bin or purchase a “biopod” on-line (see References). Biopods have drainage plates and other helpful features, but cost over $200 and do not have a distributor on Big Island. They can be shipped from Texas for around $80.
If you make your own, the basic criteria are to create a dark lidded bin with an internal ramp with a pitch of at least 30 degrees (this is so house fly larvae can’t get out) that empties into a bucket or directly into your chicken area. Screened drainage helps keep the contents from getting too wet. Start the bin with the lid open and add a few handfuls of compost to attract females. Once you see a female, you can close the lid. You will have fruit flies and house flies at first, because their eggs hatch quicker than soldier flies. Once the soldier fly larvae are established, they dominate their competitors, and other flies stop being a nuisance.
To feed 8 to 12 chickens, add around a square foot of compost per day. This should yield around one pound of grubs in several weeks, depending on temperature and daylight length. See what your bin can handle - if the waste is mostly uneaten from one day to the next, adjust by adding less compost. If it gets too wet and stinky, improve your drainage and add dryer compost. If it is too dry and ants are colonizing the waste, add damper compost. Do not go over a depth of 4 inches of waste unless you have at least 1 inch of grubs in there.
Around 5% of food waste is not converted into the larvae’s bodies and is left as compost. Although this is not as rich in nutrients as worm castings, it still is a useful fertilizer and has been used for growing orchids and mushrooms. When you want to clean out the bin, stop feeding until the last grub crawls out, and use the remaining compost.
Happy grub farming!
Much of this information is from Natural Farming talks presented by Robert Olivier in October 2011 - “Why Farm Insects” and “Raising Black Soldier Flies” : http://naturalfarminghawaii.net/2011/10/black-soldier-flies-presentation-by-robert-olivier/
Robert Olivier’s website from which you can buy larvae bins and composting supplies: http://www.compostmania.com/
General information: http://blacksoldierflyblog.com
Rachel Laderman moved to Hawai'i Island three years ago to farm and live off-grid in a small community of friends and family. Before this she worked for 20 years as an Environmental Health Educator in Olympia, Washington. She feels extremely lucky to be able to spend her days planting, foraging, and preparing foods. Read her blog at http://marketlessmondays.wordpress.com/.