Dried corn kernels soaked in water are the best bait for attracting BSF females that I have tried. I’m currently using a batch that I began soaking over a month ago. Once fermented, the corn and water give off a strong sour smell that is great for attracting black soldier fly females.
Once the BSF are established the result is a nearly odor-free process, but in the beginning it’s best to have a strong odor so the females can locate the unit. I like using fermented corn because even though it has a strong odor I don’t find it as offensive as most rotting food. It’s not a smell that I necessarily like, but it’s one I can live with during the set up phase and once I’ve got a dense colony I can go back to the normal, mild and pleasant odor of a balanced BSF composter.
One advantage of this method is that you don’t need to deal with food scraps which tend to become moldy and also attract a lot of undesired species. I did see a few fruit flies and other small flying insects in and around the corn, but compared to other baits I’ve used corn is best in this regard. Most notable is the absence of blow flies and to a great extent, house flies.
I’m using two techniques based on this idea. I have small buckets of soured corn and water in a few places and BSF females are laying eggs in the buckets. Some eggs are laid on the bucket walls and others are laid on the dry corn that’s above the water line. The resulting larvae should be able to develop in the buckets, as long as the corn isn’t completely submerged. When there are a good number of larvae in the corn/water I’ll remove and reserve the liquid and use the corn and larvae to seed a new BSF composting unit. The corn will eventually be consumed by the larvae in the new unit and the liquid can be used alone as an attractant if needed.
The strained liquid can be used to help attract BSF females directly to new composting units. Attracting egg laying females is automatic if you have an established colony, but it is the biggest challenge in establishing a new unit. Adding the corn liquid to other scraps you place in a new unit will increase the attractive odor of the bait. Also, if you live in an area that has a limited BSF population or a cool climate this attractant might help you maintain a denser colony throughout the mating season by directing more females to your composter.
I’m sure there are many other foods that could be used in a similar way. I used corn because I can buy a 50 pound bag (22kg) for about $8 at the local feed store. The key is to develop a strong smell that will represent a food source to the female BSF who are searching for an egg laying site. I’ve been told by people in the Philippines that BSF are often found in rotting coconut meat. I imagine that if you applied the principle I described above with coconut as the base that it would also work well. Likewise, I noticed good results once after adding sour milk to a unit. Your goal should be to have a bait that you can smell from a few yards/meters away. If you can smell it from that distance the BSF will have no trouble locating your composter.
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