Vermicomposting Bin: Worm Population Dynamics

Bin Conditions

Bin temperature 22 °C

Bedding moisture 70%

Feed rate 200 g/day

Simulation speed 1 day/s

Colony Status

Thriving — near-optimal temperature and moisture.

Worm population

300

Waste in bin

0 g

Castings produced

0 g

Day

0.0

How it works

Vermicomposting uses Eisenia fetida (red wiggler) worms to digest organic waste into nutrient-rich castings. The colony follows logistic growth gated by two bell-shaped tolerance curves for temperature and moisture, exactly as observed in real worm bins:

dN/dt = r_max · f(T) · f(M) · N · (1 − N/K) − d(T) · N
f(T)  = exp( −((T − 25) / 9)² )      optimum ≈ 25 °C
f(M)  = exp( −((M − 75) / 20)² )     optimum ≈ 75% moisture
d(T)  = 0                for 5 °C ≤ T ≤ 35 °C
d(T)  = 0.35·(35−T)/5     below 5 °C or above 35 °C  (cold/heat kill)

Each worm processes roughly its own body mass in waste per day (feeding rate ∝ population), converting about 60% of consumed waste into castings and releasing the rest as CO₂ and water vapour. Waste added faster than the colony can eat it simply accumulates in the bin; a colony with no waste left slowly starves and its growth term stops contributing.

Temperature — worms are most active near 25 °C; growth stalls outside roughly 10–30 °C and the population actively dies below 5 °C or above 35 °C, the same thermal kill zone that makes hot (thermophilic) composting unsuitable for worms.
Moisture — bedding needs to stay like a wrung-out sponge (≈ 60–80%); too dry and worms cannot breathe through their skin, too wet and the bin turns anaerobic and sour.
Feed rate — organic input the colony must keep pace with; overfeeding builds up a rotting backlog, underfeeding caps population growth via the carrying capacity term.
Carrying capacity K — set by bin volume (≈ 2,000 worms here), the same density limit commercial worm farms design around.

Real-world relevance: this is the same population model small-scale and commercial vermicomposting operations use to size bins and predict castings yield from feedstock and climate control.

Worms (Eisenia fetida) Waste / bedding layer Finished castings

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