Week 4 Tutorial: Sizing the insect unit against a scrap stream

Week 4 tutorial — work out how much larval biomass your household's waste can actually make, and draw the import arrow that most diagrams leave out

18 March 2027

Time

90 minutes in the room, plus about 30 to tidy the output

Graded

Checkpoint 3 of 10, 2 % — a good-faith attempt at the output below

Due

5 pm, 19 March 2027

What this tutorial is for#

The most-drawn arrow in permaculture is scraps to larvae to fish. Today you size it and find out what fraction of the feed it really covers.

Story stage. Scoping. The 380 kg waste figure is a published per-household convention, not a measurement of this house — which is exactly why it belongs on your measurement register.

Open these first#

• Your workbook, sheet 1, for the household food-waste figure.
• Week 4’s lecture for the threshold temperatures and the thermal factor for each site.
• Your home’s constraints on its dossier — some sites will not allow an outdoor larval unit where you would like to put it.

If you missed week 3#

You do not need week 3’s output for this. You do need the household waste figure from sheet 1: 380 kg a year, the course convention for two adults and two children.

The words this week uses#

• BSF — black soldier fly, Hermetia illucens. Larvae eat wet organic waste; the adults do not feed.
• Bioconversion — larval dry mass produced per unit of feed dry mass. This course works on a dry-matter basis throughout, so both sides are dry.
• Thermal factor — the fraction of the year your site is warm enough for larvae to develop. Their lower developmental threshold is 10.4 to 12.3 °C.
• The import arrow — the fish feed you buy because the loop does not close.

Do this#

1. Run the chain (25 minutes). Five multiplications, and everyone in the room gets a different answer because of the last one:

Write each factor on the sheet as its own row. A single multiplied answer with no working is not an attempt.

2. Then the choice that matters (20 minutes). Rear outdoors and accept your climate’s factor, or rear indoors at about 20 °C and take roughly 0.53 everywhere at the cost of a counted heating load. Canberra students effectively have no choice. Darwin students should be able to say why they would decline. If you choose indoors, the load goes on your sheet now, in watts and hours a day, ready for week 12.

3. Then draw the import (20 minutes). Every diagram in the room gets an arrow coming in from outside, labelled with a percentage of total fish feed. If yours does not, you have made an arithmetic error.

4. Route the rest (15 minutes). Meat, dairy and fish sludge do not go to the larvae in this course. Write the destination you are sending each to, and the reason. The reason is a course design rule about pathogen and vector risk in an uncontrolled household unit, and you should be able to say that rather than “because the notes said so”.

The output#

A feed mass balance with every factor as its own row, and the import line drawn in and labelled with a percentage.

Check your own before you submit#

1. Are all five factors on the sheet, each with its source?
2. Is the thermal factor your own site’s, or have you declared an indoor load instead?
3. If indoors: is the heating load in watts and hours, on the sheet, flagged for week 12?
4. Does your diagram show an arrow entering from outside with a number on it?
5. Are meat, dairy and sludge routed away with a reason written next to them?
6. Does your site’s dossier actually permit the unit where you have drawn it?

Where it goes next#

The feed mass balance goes into week 5, where it caps how much of your fish counts as yours.

Back to week 4 overview