May 182011
 

Attracting BSF (Hermetia illucens)

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.

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.

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May 142011
 

I’m testing a strategy for improving the conditions in a BSF composter based on the addition of corn cob pieces sold as hamster bedding.* Before putting any waste into the unit (in this case a BioPod) I added a 3 inch layer of the corn cob bedding which I had soaked overnight in water. The cob was placed directly on top of the drainage pad which is the material used to filter effluent (liquid waste).Possible benefits of corn cob (general)

One function I’m considering is that of a moisture buffer. When there is an abundance of liquid I picture the cob soaking it up and then retaining that moisture to help keep the compost above the 70% moisture level that I’ve read is the minimum for black soldier fly larvae (BSFL or “grubs”).

I think the sponge-like structure of corn cob may make it a good substrate for beneficial bacteria. I have fed fresh whole corn cobs to BSFL in the past and I noticed that larvae could be seen in the crevices of the cobs well after any visible corn kernel was gone. In some cases I saw this activity on cobs that had been added several months earlier. The larvae appeared to be feeding, and most of the time it was the smaller larvae. I’m guessing that they were feeding on bacteria since no food was visible. Maybe only the smaller larvae could fit into the small crevices of the cobs. I’m thinking that the sponge-like structure of corn cob promotes the presence of oxygen and therefore if bacteria were present they would be the aerobic type (thrives in the presence of oxygen). This relates to the idea that BSFL consume and derive nutrition from bacteria; something I’m not sure of. If the cob pieces promote aerobic bacteria them maybe it will help maintain overall aerobic conditions in the compost.

Drainage is always a critical issue in BSF composters, and corn cob may facilitate better drainage. Given its porous structure the cob may allow liquids to pass through the otherwise dense residue created by BSFL. This is also related to anaerobic bacteria (thrive in the absence of oxygen) which are associated with foul odors and BSF system crashes. Flooded conditions limit the oxygen present in the compost which promotes undesirable anaerobic bacteria. Therefore, good drainage is key to keeping a BSF unit balanced and corn cob may help with this.

Possible benefits (for system start up)

In addition to the concepts above I began this test with the idea that in the start up phase the cob would work as a pre-filter and keep the initial waste off of the filter material. To be honest I wasn’t exactly sure if there was any benefit in that, it was more of a hunch or a guess. The concept of a pre-filter morphed into something else, more on that below.

Maintaining a high moisture level is always important in a BSF unit, but it’s usually automatic in an established system which receives regular large additions of waste. In a new system with little or no larvae present the waste has a tendency to dry out, especially in dry climates. Keeping the beginning waste moist is important for two reasons; any newly hatched larvae are at risk of dehydration, and moist waste is better at giving off the odor which serves as a beacon for egg laying BSF females. The three inch layer of moistened cob was designed to increase the bulk in the new unit with something that would absorb and retain liquid without overloading the unit with food waste. After adding the soaked corn cob I observed that it too was drying out after a few days. As a result I began adding more liquid to the unit which led me to the idea of flushing the system with liquid several times per day.

Flushing a new BSF unit with liquids

When I saw the need to rehydrate the cob pieces I decided to wet it with the liquid produced when I fermented dried corn as a BSF attractant. (A favorite BSF attractant of mine is dry cracked corn covered with water and allowed to ferment. Sugar can be added to speed up the fermentation, but I have more often not used sugar.) I slowly poured approximately one gallon of the corn liquid into the unit, making an effort to distribute it as evenly as possible. As the liquid evaporated from the cob it gave off a good volume of the scent that BSF females followed back to the unit. The effect was strongest just after pouring in the liquid so I began draining the corn liquid into a bucket and re-introducing it to the unit as described above. Cycling liquid through the unit several times a day has kept the contents moist and I believe it has enhanced the attractiveness of the unit to BSF.

After 3-4 days of flushing the unit with the corn liquid I noticed that the pleasant sour smell was developing a less pleasant odor that I think indicated growth of anaerobic bacteria. At that point I stopped recycling the liquid and began flushing the system with fresh water. 4-6 times everyday I’m draining any liquid in the unit and adding it to my tomato plants, and then adding 4-6 quarts of fresh water evenly over the corn cob pieces and waste. I don’t drain the system immediately, I have been leaving the newly added liquid in the bottom of the unit as I believe it will help keep the ambient humidity within the unit higher and increase the attractive odor which helps attract BSF.

Going forward

I anticipate that as the volume of waste increases, the churning action of the BSFL will mix the layer of cob evenly throughout. My hope is that the cob will continue to help keep the unit aerobic and improve drainage. I plan to continue flushing the waste with fresh water until I see some indication that it is having either no effect or a negative effect. I’m very curious if it might make for a more stable system. At the least it would serve as a constant indicator of how well the system is draining.

I’ll add photos and videos soon.

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Since we now have a discussion forum we will be disabling comments here on the blog. Anyone can read the forum, but to join in on the conversation you will need to register. This is an easy and painless process, and it’s necessary to keep spammers from, well, spamming up the place. :)

The forum can be accessed here (forum) and you will see a link for registration in the upper left corner of the forum. The legal language on the registration form is very basic and is what came with the forum software. In short, we won’t share your information, and please don’t be vulgar or break the law. ;)

Apr 132011
 

EDIT: I’m sorry to say that we will probably not be shipping starter kits this year. If you have a good source you would like to recommend please feel free to do so in the comment section.

We’re beginning to get a lot of inquiries about BSF starter kits as usual for this time of year. In previous years we produced and sold a kit but we haven’t decided if we will do so this year. We will post our decision here as soon as possible. Thanks!

 

Apr 282010
 

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.

Update: Since we now have a discussion forum we will be disabling comments here on the blog. Anyone can read the forum, but to join in on the conversation you will need to register. This is an easy and painless process, and it’s necessary to keep spammers from, well, spamming up the place. :)

The forum can be accessed here (forum) and you will see a link for registration in the upper left corner of the forum. The legal language on the registration form is very basic and is what came with the forum software. In short, we won’t share your information, and please don’t be vulgar or break the law. ;)