Challenges in crawl off

Ok, so the larvae ate all they can eat and now nature is telling them to climb up and out of the food. I was getting hundreds of crawl off, and I had no idea how to create a structure for them. Finding information on it was difficult. Substrate? Container? Environment? All I knew was "dirt". They want to get out of the food and into dirt, bury down, then reemerge as flies. I was familiar with what the larvae need. I had an idea of what the flies required. What the hell do the crawl off need?
I wanted to build a big terrarium to accommodate the trays and then later the flies. It would be a one-shot deal to serve two stages of the BSF (black soldier fly) life cycle. My shoddy attempt at a large terrarium was a large wardrobe box (from my move), lined with sheets of plastic that I duct taped on, and then netting over that. Flaws included: too drafty to keep humidity high, difficult to lift trays in and out, just plain ugly. I needed something more specialized for the crawl off as well as the flies. This cardboard box didn't work in any respect.

So to cater specifically to the flies, my terrarium solution was to downsize to plastic storage bins. I bought two large bins, duct taped the top one upside down onto the bottom one to create a seal, then cut an access hole in the side of the top container, covered it with netting and then draped plastic over the opening. And it's all bungee-corded secure. It's not too ugly, and I can keep it down near the wood stove to maintain high temps for the flies.

The fly terrarium. It sits on top of the smaller plastic bins that contain the crawl off. I go through these every night. 

Now back to the crawl off.

Containment attempt #1: plastic planter pots. The amount of larvae quickly overwhelmed the size of the containers. Stacking was impossible. Also they found the holes in the bottom of the pots and made quick use of them.

Containment attempt #2: seedling trays filled with dirt and then stacked. I could easily dump 100 larvae in. Stacking devolved into squishing the bottom trays. The larvae escaped regularly. We found them on the hallway floor, the bathroom floor and on the kitchen floor. Well-traveled little buggers.

I had these seedling trays and I thought maybe I could come up with a rack system on wheels. That didn't solve my escape issue though. After walking around various hardware stores, Surplus City and then the dollar store, I found it...

Containment attempt #3: $1 plastic shoe bins with lids. I have 25 of these that are filled with various substrates (dirt, mulch, saw dust), and the crawl off are added as needed. They stack easily. The price was right. Not too ugly. No escapees, sort of.

63 larvae ready to burrow down

After about a minute, they've nearly vanished

Monday, November 28: I came home to the wood stove roaring hot and discovered that the larvae were so uncomfortable that they squeezed between lid and container and were getting out of the plastic bins. I had to wrangle larvae yet again. I frantically went through the containers, collecting them out of the carpet. Then something buzzed up into my face and then circled the lights. FLIES! Finally. Jeez. And I collected my first batch that night.

I think the flies are rather pretty. Their wings are a dark iridescence. 

An empty pupa shell

After two months of fly collection I've noticed that the temperature of the substrate seems to impact hatching. A day when the wood stove doesn't get much usage will yield a lower fly count. Also, substrate moisture is important. I think this was a contributing factor to larvae escape in the seedling trays. They need moisture for proper wing development.

Temporary containment for the flies until I could get them into the terrarium: Jif jar

I'm not sure how it's possible, but I'm still collecting flies from crawl off that went into bins in early November.