20,000 Larvae Under the Screen

(Good title right? I've pretty much peaked on that one, just a warning.)

If you would have asked me a year ago if I would be concerned about the sex life of a fly, I would have laughed. And yet here I am. I was flummoxed that I couldn't keep the circle going. The flies weren't mating. Therefore no eggs. Therefore no next generation of larvae.


Spring brought me so much optimism, but the flies weren't feeling it. Something was missing in their artificial environment. I didn't want to have to order more larvae. I was really hoping this would have been a slam dunk: larvae eat, crawl off, emerge as flies, flies mate, lay eggs, every last one of them hatches happily, repeat forever. False.

I decided that the flies were lacking a key indicator: a healthy, thriving larvae colony. So, on May 12, 20,000 small larvae arrived in the mail. That would be twice as many as I had ordered back in September.

May 12: The first meal for the larvae

The larvae came and I focused on feeding and observing them instead of fly collection, which had slowed down significantly. They ate voraciously for about a month. They cleaned a pumpkin down to the rind in two days. The larvae were housed in two 11 gallon troughs covered with a burlap bag. (I understand that this makes the post title invalid, but it didn't work with my pun. It's the same concept though.)

May 21: Larger and ideal for fish bait at this stage

And then the crawl off. The troughs didn't offer an easy exit for the prepupae, but I could tell that they were ready to move to the next stage. Very little food was consumed, and they gathered in the corners. I tried to break them up into different troughs filled with sawdust for their emergence bins. I left for one hour and came back to prepupae all over the floor. I dumped all contents of the three troughs into a 55 gallon barrel that used to have peanut butter in it (another Surplus City find.) After a day of them circling the perimeter, they settled.

On June 18, the first fly emerged. I knew this day would come. The tank that I was using for the flies would not fit the coming 20,000. I had to upgrade. I also now needed to keep a mosquito net over the barrel.

Fly collecting while a sleeve of flies forms on my arm.
You can't see it, but I'm draped under a big green mosquito net while I do this

Mom had purchased a small greenhouse unit (18" x 27" x 60") which was a basic frame with shelves. I screened in one side and then wrapped the whole thing in plastic. It seemed like a good upgrade, but there were no eggs. I decided it wasn't big enough, so I made another one and with a few modifications.

Fly House #1: I made some adjustments for the second one

Some larvae didn't make it, and some flies won't emerge, so to expect 20,000 flies isn't realistic. I don't know how many flies I collect a night, but it's probably close to 400. Even if that's a generous estimation, that is at least 40 days of hearty fly collection.

On June 28, I made the second fly house. I stayed up way too late but it was necessary to keep up with the quantity of emerging flies. The very next day I witnessed at least 20 mating pairs in the new house. And then I noticed eight or so pairs in the old house. Typical. A female laid eggs in the inconvenient location of the water catch dish that is attached to the plant pot. Mom and I had to pry them apart to collect the thousands (!) of eggs.

Fly House #2 is online as of June 28 (photo taken July 4).
 This upgrade made me hate Fly House #1
and I redesigned that based on this setup

Fly House #1 redone on July 4

Detail shot of #2

This is a small representation of the collection of egg clusters on July 3.
There will be thousands

Here's a fun side story about the peanut butter barrel. I've had this thing sitting in the garage for weeks in the garage with nothing disturbing it. Then one day I go out and see that the ants have found it. I sat out ant traps after I moved it 20 feet. The next day a large spider was down in the barrel. The day after that, I came home and Dad informed me that there were a dozen or so flies at the garage door window. I checked the barrel and a hole was chewed through the mosquito net. The cutest little mouse was now trapped at the bottom. I attempted to scoop it out, but it ran and dove under the sawdust. It didn't resurface that night. I braced myself for what I'd discover the next day, since the intruding creatures were getting bigger every day. But it was still just the mouse. I scooped it out without too much trouble and set it free.

One of these things is not like the other

A freed mouse gets a new lease on life