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BSF Metrics #2 — Rearing Cycle Length: Why Extra Days Kill Your Margins
BSF Metrics That Actually Matter — #2 Rearing Cycle Length
01 · Throughput
Cycle length is a throughput multiplier
"Harvest at day 14." Common advice. Not wrong. Just expensive.
Cycle length is the throughput multiplier hiding inside your OPEX. It's a tradeoff between three things: how many larvae you put on the substrate, how big they end up, and how long they take to get there.
02 · The tradeoff
The tradeoff most operators miss
Same substrate, same total larvae mass — whether you start with 8,000 or 15,000 per tray.
Fewer larvae → each grows bigger. Cycle drags.
More larvae → each is smaller. Cycle finishes faster. Space frees up sooner.
So the real question isn't "how big are my larvae". It's: what costs you more per ton produced — the larvae themselves (5dol cost), or the rearing space they occupy (daily OPEX/m²)?
Most operators don't know their daily OPEX/m². That's the first calculation to run.
03 · The math
The throughput math
Same module. Same rent.
- 8-day cycle → ~3.75 batches/month
- 14-day cycle → ~2.1 batches/month
- 44% less output.
For 5–10 modules, that's the difference between a viable business and a money-losing hobby.
04 · The rule
The 8-10-14 rule, from 8+ years of cases
- 8 days — your target on real biowaste in a climate-controlled room.
- 10 days — acceptable, but something is off. Investigate.
- 14 days — maximum. Reject the recipe, or get paid to handle the biowaste.
- Under 7 days on real mixed biowaste — unrealistic. Ask to see the data.
05 · Climate
Climate is non-negotiable
Doesn't have to mean HVAC. The target is substrate temperature ≈ 30°C. Not air. Substrate.
Air varies across the cycle. Hotter early — wet substrate cools itself by evaporation, so air runs ~4°C above the substrate target. Below 28°C late — larvae generate metabolic heat from inside. Ventilation does most of the heat exchange.
A common trap: substrate dries too fast. Larvae stop eating. Batch looks "ready" but is stranded. Throughput collapses. Keep humidity above 70% RH.
06 · The recipe
The starter recipe
- Aim for an 8-day cycle.
- 8 kg substrate per 600×400 mm tray (9 kg only if moisture is high).
- Start at 10,000 larvae per tray. Adjust until 8 days hits.
- Weigh. Calculate OPEX per ton produced.
Density band on 8 kg good substrate: 7,000 floor / 10,000 rule of thumb / 15,000 ceiling. Outside that, fix climate, recipe, or substrate quality first.
Target ≥150 mg per larva at harvest. About 1.5 kg from 8 kg substrate — a ~5:1 ratio.
07 · The early signal
Cycle length drifts before BCR drifts
Track it for every substrate change, every season, every new waste source.
What's your daily OPEX/m² of rearing space? And have you matched it against your larvae cost per ton produced?
Keep exploring
Related topics and pages
- BSF Metrics #1 — Bioconversion Ratio — the previous metric in the series
- BSF metrics series — the seven-post series this cycle-length post belongs to
- Production capacity in BSF farming: Realistic output metrics that actually hold — the density and output numbers that set the cycle target
Read next
- BSF Metrics #1 — Bioconversion Ratio — the previous metric in the same seven-post series
- BSF metrics series — the teaser that introduced the whole metrics series
- Production capacity in BSF farming: Realistic output metrics that actually hold — the density and output numbers that still hold in practice
- KALARVO Recipe-Testing Field Post — a field note from the recipe-testing work behind these cycle metrics
Next step
Check the cycle on your own material
Manna can help measure the rearing cycle and daily OPEX per square metre for a specific material and operating setup.