Attracting black soldier flies-the basics
Originally posted on the blog: Post
Attracting the initial black soldier fly (BSF) females to start up a BSF composter can be problematic if you don’t understand the basic principles involved. Of course the first step is to determine if your area is populated by BSF, but once you’re satisfied that they’re present it shouldn’t be too difficult to attract them. As always; please keep in mind that I’m not an entomologist and what I write about BSF is part educated guess and part practical experience.Realistic time frame
Often people are successful at inoculating their composters before they even know it. It’s important to understand that it can take 2 – 4 weeks from the time that eggs are laid until you can easily see the resulting larvae or “grubs”. Sometimes you can see clutches of eggs laid in the corners or crevices of the composter or bait container, however, often the females randomly scatter their tiny eggs on the inner and outer walls of the unit. That makes it almost impossible to see them without magnification. The newly hatched larvae are also tiny so after the bait (food scrap) has been out for several days they could be present without being obvious. For that reason it’s usually not wise to throw away any existing bait and start over; you may very well be discarding recently hatched larvae. Below is a photo of a black soldier fly larva (BSFL) on the sixth day after it’s egg was laid which makes it approximately two days old. You just can’t glance at a pile of rotting food and know if these little creatures are present or not.
Choosing the menu
BSF life cylce day 6 w.jpg [ 82.3 KiB | Viewed 2178 times ]
Larvae of the black soldier fly (Hermetia Illucens) are designed to consume decomposing plant or animal material, or partially digested food (manure). If you set out fresh food scraps you won’t have a good chance of success until it begins to break down somewhat. You will always attract other fly species in the beginning, but once the BSF population expands to a high density they will dominate the waste causing other species to avoid it. Fruit, vegetables and grain can be used as bait but I don’t recommend adding meats until after you have established a dense colony.
You can attract BSF with a variety of foods but my favorite method uses grains. The reason is that they are easy to ferment and relatively stable, meaning they don’t become anaerobic (sewer-like odor) too easily. At least that’s how it appears to me. Anaerobic bacteria thrive in the absence of oxygen and BSFL do not do well in that type of environment. While you don’t want foul odors I do recommend using a strong sour odor to attract BSF females. I assume they follow a scent trail to the food source so I try to use a bait that I can smell from a few feet away. The difference between a sewer-like odor and a sour odor may not be clear to you immediately but we all understand the stink of a sewer and you don’t want that. I usually start with plain dried cracked corn from the feed store which is sold as chicken feed. It is covered in water and soaked for a few weeks before using it. I do this outdoors in a container with a tight fitting lid. The odor resulting from the fermentation is very attractive to BSF because the sour grain is a good food source for them. I have a post about using fermented corn here: Attracting BSF with cornKeep the bait moist
One very good reason to keep the food scraps moist is that any larvae that might have hatched will need approximately 70% moisture to thrive. Another reason is that moist bait will give off a stronger scent trail than bait which has a dry crust on it. When I use fermented corn I keep it completely covered with water. If you’re keeping the bait in your composter with a filter pad I recommend temporarily installing a container to hold the bait so that you can more easily keep it moist. Below are photos of one approach I used in a BioPod Plus. The first photo is after two days and the second was taken a few weeks later. As you can see it would have been much more difficult to keep the scraps moist if they were sitting directly on the filter material. Shortly after the second photo was taken I added the waste and larvae directly to the composter. (What may look like large BSFL in the first photo is actually puffed rice.)
I didn’t use fermented corn in these photos because I didn’t have a batch ready. A few days after the the last photo was taken I placed a small container of fermented corn with its liquid inside the composter with the other waste. I already had larvae by then but the goal is to keep as many females coming to the composter as possible during the early stages. Once you have a dense colony established plenty of females will visit the unit to lay their eggs without any special effort on your part.Keep the bait warm
The common wisdom is that a BSF composter must be kept fully shaded. This is true in most cases but there are notable exceptions. Just as you will produce a stronger scent trail by keeping the bait moist, you will also produce a stronger scent if the bait is warm. For that reason I kept the composter in the above photos in full sun during the period in April and May when I was initially attracting BSF. I would have chosen a shady place if this had been during the middle of the summer, but during the cooler days of spring a sunny spot worked better. The rule to remember about temperature, and sunny versus shady location, is simply this; try to keep the temperature inside your BSF unit roughly between 70ºF and 100ºF (21-38C). The generally accepted range that BSFL can survive is between 33ºF and 115ºF (1-46C). Our goal here is to keep them warm enough to stay active but cool enough that we don’t approach the fatal heat level. The reason overheating is such an issue in a densely populated composter is that the larvae generate a lot of heat as they metabolize waste. In a unit that has no larvae yet or is thinly populated overheating is only an issue when daily (ambient) temperatures are very high.Divide and conquer
It makes sense that your odds of successfully attracting BSF females will be higher if you set out bait in multiple locations on the same or different properties. Of course you can choose to attract BSF directly to your composter, but using a separate container for bait makes it easier to experiment with different locations if you don’t want to move your composter around. While you can use almost any container for the bait you will probably have better results if you use something that supports the goals of keeping the bait moist and warm. It’s also a good idea to prevent excessive rainfall from entering and flooding or diluting the food scraps. Your attractor unit can be as simple as a bucket with a lid and few holes cut into the sides. I’m currently testing a design that uses a common plastic coffee container and I will post photos of it soon.Another alternative; don’t wait for BSF to find you
Setting out baits to attract BSF females can be very effective, but I also recommend hunting for eggs and larvae. I regularly advise people that a great way to find BSFL is to start a traditional compost pile which includes kitchen scraps or find someone who will let you search in theirs. The kitchen scraps are important because BSFL are not designed to consume high cellulose items like grass, leaves and paper. If you can collect some larvae from a compost pile you probably won’t have enough to fully populate your composter, but the larvae are a powerful attractant to egg laden females. Add the collected larvae to your BSF unit along with some of the compost they were found in. As mentioned above; keep the material moist and warm and the subtle scent of the larvae plus the odor of the food scraps will work very well.
Another option is to hunt for BSF eggs which are then added to your composter. You can often find eggs that have been laid on household garbage cans. To be honest this is the most frequent method I use for starting new units in the spring. Consider that a typical garbage can has all of the elements to satisfy the basic requirements for attracting BSF; they contain decomposing food, and they tend to be moist and warm inside. When I want to attract BSF I leave one of our garbage cans full for an extended period so that it starts to give off a noticeable odor. In my experience it works like a BSF magnet. Since we use black can liners the light colored eggs show up very clearly. I take an old knife and gently scrape the clutches of eggs into a small lid or shallow container and place it in the composter on top of the food scraps. When the larvae hatch they will crawl into the waste and begin eating.
Those are the basic concepts based on my experience. BSFL eagerly consume anything that humans eat and more, so you don’t necessarily need to limit yourself to what I’ve mentioned here. I assume what I’ve written here can be improved on, but it will get you started. Check back soon if you’re interested in seeing my coffee can BSF attractor.