Actually, this post applies to any region that has seasonal temperatures below that which support BSF mating. This encompasses the entire continental U.S. except for a few extreme southern areas.
Black soldier flies (Hermetia illucens) are common in tropical and subtropical regions, but their range extends into many northern states of the continental U.S. You can easily operate a BSF bio-composting unit in northern states during the warm months, but you can also maintain the colony through the colder months with a little extra effort.
A black soldier fly colony generates its own heat
Maintaining a BSF unit in cold weather without heating it is possible because the churning action and digestion of the black soldier fly grubs creates heat as a byproduct. Under cold conditions keeping the colony at the optimal temperature range of 85° – 100°F (30°-38°C) is as simple as consistently feeding them and placing an insulating material directly on top of the pile. Simply remove the insulating material, add the food scraps, and then replace it. It’s important to feed the colony consistently in cold weather because without food the temperature will drop and the colony will become dormant. You can think of it like a diesel engine, if it gets cold then it’s hard to get it started again.
If the larvae are exposed to freezing temperatures they will die. Also, any insulation on top of the colony needs to have an air gap between it and the BioPod.
Maintaining a BSF colony during extended periods of sub-freezing weather will probably be a challenge for a novice, but it’s worth tying because at worst you’ll learn more about this fascinating creature. If you aren’t up to the challenge just yet then you can enjoy BSF culturing up to the point where the weather in your area makes it difficult and then resume in the spring. If you can store some or all of the compost through the winter it should make attracting the BSF easier in the spring.
Process more food scraps, harvest less larvae
The time it takes BSF larvae to mature increases in cold weather from the usual few weeks to a period of up to several months. I’ve maintained BSF larvae in the juvenile stage (light color, actively feeding) for five months through winter keeping the unit outdoors with some insulation. The same individual larvae will eat all winter which enables you to continue bio-composting without the need to replenish the colony with visiting females. However, since reproduction doesn’t happen at this time you must stop harvesting larvae if you wish to continue processing waste through the cold season.
In warm weather the colony has a tendency to overheat, so in cool weather the larvae are able to consume food scraps even more efficiently.
How adventurous are you?
I don’t recommend bringing the BSF unit into your living room, but why not try keeping it in the garage or a shed when the temperature drops? Sure, a few larvae might get out, but so what? The adult fly will just emerge from it’s pupae in the spring and then you’ll have the pleasure of gently capturing it and releasing it outdoors. They are harmless creatures after all. I don’t think a heated space would be the best choice though, because it might trick the larvae into developing too quickly. I would guess that 40° – 60°F (5°-15°C) is a good range to try testing this theory, and of course you would need an insulating disc of some sort to keep the colony warm. The degree of insulation would depend on the ambient temperature in the space.
I’m cursed with living in an area that rarely gets cold so if you try this experiment please let me know how it goes. I would love to post photos of your set up (if it works ).
Mike made a comment below reminding me of a presentation by ESR about BSF culturing in winter. Here is a link to that article: http://www.esrla.com/winter/frame.htm