Notes from Windward: #67


Magic Worms

sustainability's tiny alchemists

[Note: this is a continuation of an article from last year's Notes.
To view that article, Click Here.]

  March 23:

     When last we spoke about our magic worms, we were in the process of putting them to bed for the winter. They're cold blooded, so as the weather gets colder, they go dormant to await the return of warm weather. They function best in the 80-85° F range, but so long as they don't freeze, they'll bounce back.

     Since this was our first attempt at over-wintering BSFL, we tried a couple of things. For example, we gathered up a hundred pupae that were earnestly trying to climb out of the old chest feezer we're using as a confinement are, and transfered them a small, screen covered terrarium that we tucked away in the back corner of the kitchen. That way we knew that we'd have a good start on a breeding population, regardless of how cold it got in Vermadise. We cut out a piece of foam insulation to fit the inside of the terrarium, and the pupae crawled under that and went to sleep for the winter.

     Now that the day time temps in Vermadise are getting up into the 80's, we starting to see the emergence of adult flies. They're easily differentiated from house flies in that they're long and sleek, whereas house flies are squat and dumpy.

     We took that as an indication that it was time to move the pupae stored in the kitchen from their hide-away in the back to a more sun-filled location in one of the kitchen's two bay windows. These windows are where we do much of our seed starting, and we're hoping that it will serve as well this year as a place for our emergine adults to get started as well. Each day more of the pupae are responding by crawling out from under the foam to bask in the sun, and now they're just laying there with their little tails curled up--a sign that they're not dead, just busy morphing. The process of morphing into adults which takes about two weeks at 85° F. Since it's not that warm in their enclosure, it may well take longer for them to make the transition.


     By next spring we expect to have the propagation greenhouse on line. It will be a smallish structure covered in poly-carbonate and resting on top of a 1,250 gallon water tank that we'll be heating with thermal solar panels. The idea is that the water tank will act as a huge "hot water bottle" to keep the green house warm at night.

     The adult flies need natural light and space to fly around and conduct their mating dance, so the plan is to use the propagation greenhouse--generally intended for the sprouting of seeds and the rooting of cuttings--to be the Black Soldier Flies "honeymoon cottage" where they can start mating and laying eggs sooner than would be the case in unheated Vermadise.

     Time will tell how all that turns out, but for now we decided to cover our bets by ordering in another seed stock of small larva from Mulberry Farms. This way we'll have half-a-thousand larva working as soon as it gets warm enough inside the chest freezer, instead of having to wait for enough adults to merge, mate and lay fertile eggs. Since they can't eat or drink (the adults don't even have a mouth) the adult flies only have a three day window within which to dry off enough for their wings to work, find a mate and then find an appropriate site where they can lay their eggs so that the very tiny hatchings--each about the size of a grain of flour--can crawl to a food source.

  March 26:

     In the short time since their arrival our new batch of larva have doubled in size, and as the weather warms Vermadise, they're moving around quite a bit. For reasons that aren't clear to me, the larva--just like the pupa before them--are proving to be able to climb the virtical walls of the vault when they're only "supposed" to be able to handle a 45° incline.

     My guess is that they're searching for heat since the bottom of the vault has only warmed up to about 50° F., while the air temp in Vermadise is in the 80's in the afternoon, and being cold blooded, the warmer it gets, the more active they get.

     In order to try and contain the larva, we decided to install the sort of flashing that comes in an "L" shape with an additional down turn on the edge to help it shed water. In this case, we're hoping that it will shed larva just as well.

flashing in place on one side of the chest freezer

     To affix the flasing, we used pop-rivets since that type of fastener often produces the strongest bond between two thin pieces of metal.

Gina pop-rivets another length of flashing in place

     Once a lip had been created all around the top of the freezer vault, we drilled an exit hole and created a ram for the pupa to use to exit the vault.
the exit ramp pop-riveted in place

     A 90° plastic pipe fitting was fitted into place at the end of the exit ramp so that the pupa would be guided down into the plastic collection container. Whatever is allowig the pupa and larva to climb the walls of the vault most likely has to do with the nature of the surface. It was corroded, so we wire brushed it and painted it with Rust-Oleum, and I'm guessing that the underlying surface is rough enough that the little guys can get a grip on it.

the plastic elbow that guides the pupa into the collection bucket

     Meanwhile, you'll remember that we over-wintered a few hundred pupae in the kitchen so that if the ones in the chest freezer were killed off by the cold, we'd still have a population to work with in the spring. Now that the kitchen is warm enough that we don't need to start a fire in the morning, we've moved the pupae from their small containment in the back of the kitchen to a larger containment in the one of the bay windows.

the pupae basking in the sun

     Within a day, lots of pupae had crawled out from under the block of foam insulation they were hiding under, to bask in the warmth of the sun. They morph into adults best when the temps are above 80° F, and you can tell that they're undergoing metamorphasis (as opposed to being dead) because their tails bend down.

     It takes about two weeks for the metamorphosis to happen and for the adults to emerge. It takes another day for them to dry their wings and become ready to fly, at which point we're hoping that the cage they're in will be large enough that they'll be able to mate. Just to be prepared, I cut up and introduced some card-board since the holes are just the right size for the females to lay their eggs in.

cardboard cut and stacked for egg laying

  April 5:

     As the weather warms, there's lots of things happening in the larva vault. Because houseflies are better able to handle cold weather than the more tropical BSFs are, they've laid lots of eggs inside the vault and their larva are really going to town processing the materials that accumulated over the winter. The catch is that housefly larve don't have the nifty little hook that allows BSF larve to climb a steep exit ram (the hook functions sort of like a mountaineer's ice pic) and so they're doomed to remain in the vault, never getting the chance to undergo metamorphosis. All they're doing is pre-digesting the waste for the BSF larva to come.

BSF adults waiting around for their wings to dry

     For the past week BSF pupa have been arriving in the catch bucket, and today the new pupa were accompanied by some fully developed BSF adults emerging from their shell (puparium). It takes a half-day for their wings to dry to the point that they can fly, but for that bit of time, they're fairly easy to spot once you know what to look for.

  April 12:

     Still learning how to operate the larva vault, but it looks like things are settling down in there as the larva finish catching up with the thawing kitchen waste. Since the larva can go for months without eating, activity in the vault reaches a sort of equilibrium where everything is on hold pending the arrival of something else to eat. Yesterday, Gina found one of the chicks dead in the chicken run, and tossed it into the vault. It isn't there today.

     The volume of waste in the bottom of the vault has decreased by about a third as the larva work it through their system, and for the past couple of days, the level of waste and larva has dropped below the bottom of the exit ramp. The result is that the number of pupae making it into the catch bucket has dropped off.

     So, for the past two days I've just taken the chick's larva bowl and scouped out a few cups of larva for them to enjoy. I need to fetch some more sawdust from the woodshop and bring the level back up to the point where the pupa can get to the ramp. The sawdust will help absorb moisture and the nitrogen given off by the larva, moisture and nitrogen which will enable bacteria and fungi to break down the sawdust to form more nutrients for the larva to comsume.

     I know that larva are "yucky" but the more I work with them, the more I'm coming to respect these little dynamos and the role they can play in sustainability.


     Where as they were shy a few days ago, by now the chicks mob the larva bowl in an effort to get a share of the larva. You can't see it but there actually is a nine inch wide bowl under that mass of chicks :-)

     If you look close, you can also see that "mystery chic" is doing fine, and is right in there competing for a share of the larva.

  April 15:

     Todd was telling me about how sterilized saw dust is used for growing out mushroom span because of the high surface area to weight ratio, which triggered the thought that the larva vault would benefit from a load of saw dust as well.

      As the larva work their way through high-protein waste, they give off ammonia notable quantities of ammonia. Concentrations of ammonia are not only unpleasant, but they can be unhealthful in that when the pH of lung tissue rises, the lungs become more susceptable to various phumatic infections.

     Yesterday I added ten gallons of saw dust to the larva vault, mostly piled up towards the end with the platform that leads to the exit ram. When I checked on the vault today, the sawdust had been evenly distributed across the surface of the valut, and the larva seem right at home in it. Most importantly, the ammonia smell was greatly reduced.


     The sawdust also offered an aesthetic benefit because now you have to look close to see the larva swimming through the sawdust.

      Since the total amount of material in the vault was still lower than the start of the exit ram, I added another ten gallons of saw dust today, and will continue adding more until the general level of material in the vault is about ten inches deep. The sawdust also adsorbed the surplus moisture that had been accumulating in the vault as the larva broke down the waste.

     BSF larva don't digest cellulose, so the sawdust isn't food for them, at least not directly. The moisture and ammonia that the sawdust absorbes will enable bacteria and fungi to break down the cellulose into products that the larva can digest, so ultimately, the sawdust will turn into more food for hens and fish.

     It's the same sort of biological breakdown that would happen outdoors naturally, it's just that in the larva vault it's happening much, much faster.

  April 18:

     We've made excellent progress towards getting a stable niche ecology going in the larva vault. The addition of sawdust has taken care of the surplus nitrogen given off by the larva, and their numbers have increased to the point where there's nothing much left to smell since when new scraps go in, they're pounced upon so fast that there's not enough time for anything to actually rot.

     The nxxt problem we need to deal with involves a build up of liquid in the bottom of the vault. It's not intuitively obvious, but water constitutes more than half of the total weight of everything from table scraps to a dead chicken, so as the larva break things down, one result of their work is the accumulation of a good deal of water in the bottom of the vault.

     That's a problem in that standing water in the bottom of the vault can lead to anaerobic conditions--not good--but more than that, we found that when the sides of the vault are damp, the larva can use capilary action to hoist themselves straight up the vertical walls as they try to make good their escape. Also, I'm sorry to report that the flashing we installed wasn't working very well because we used latex caulk to seal it, and the larva were able to use the dampness to hike up there and eat the caulk <sigh> The current plan is to dry out the vault and recaulk the flashing with a silicone caulk that--I'm presuming--won't be as tasty.


     We decided to deal with the build up of moisture in the vault by venting it. The first step was to drill holes in the back of the vault and the side of Vermadise, and install a 1" hose between the two. The type of hose we installed is called "suction hose." in that it's strong enough to hold a vacuum without collapsing. That rigidity allowed us to bend it in a roller-coaster style loop that should make it difficult for larva to exit the system. The diameter of the hose is large enough to allow gravid females attracted to the vault to make their way inside to lay eggs. Each female black soldier fly will lay about 900 eggs, and we're feeding a couple hundred larva a day to the chickens, so we don't want to interfere with egg production.

Notes From Windward - Index - Vol. 67