Earthworms

"The plow is one of the most ancient and most valuable of man's inventions; but long before he existed the land was in fact regularly plowed, and still continues to be thus plowed by earthworms." — Charles Darwin, The Formation of Vegetable Mould through the Action of Worms (1881)

Darwin spent 40 years studying earthworms. Here's what he (and 140 years of subsequent science) found.

What Earthworms Do

Activity	Impact
Casting production	Casts contain 5x more N, 7x more P, 11x more K than surrounding soil
Tunneling	Creates macropores for air + water movement — key drainage function
pH buffering	Casts are near-neutral pH regardless of surrounding soil
Pathogen suppression	Gut enzymes kill many soil pathogens during digestion
Decomposition acceleration	Physically break down organic matter → faster bacterial action
Soil mixing	Move 10–40 tonnes of soil/ha/year from subsoil to surface

Earthworm Population by Farming System

System	Earthworms per m²
Healthy organic/forest soil	200–500
Average mixed farmland	50–100
Chemically intensive	5–15
Monoculture with pesticides	Near zero

Field diagnosis: Dig a 30cm × 30cm × 30cm cube of soil. Count earthworms.

• >10 worms: Good soil health
• 5–10 worms: Moderate — needs organic matter
• <5 worms: Poor — chemical damage or compaction likely
• 0 worms: Severe degradation — emergency intervention needed

Why Earthworm Populations Collapse

1. Synthetic pesticides — organophosphates and carbamates are acutely toxic to earthworms; herbicides disrupt their gut microbiome
2. Tillage — deep plowing physically kills worms and destroys burrow networks
3. Bare soil — no food (earthworms eat organic matter and bacteria)
4. Compaction — physically prevents movement and tunneling
5. Waterlogging — earthworms drown in anaerobic conditions
6. No organic matter — starvation

How to Restore Earthworm Populations

Step 1: Stop What's Killing Them

• Stop synthetic pesticides (especially herbicides, nematicides)
• Reduce tillage depth — switch from 20–30cm to 5–10cm maximum
• Prevent compaction (avoid heavy machinery on wet soil)

Step 2: Feed Them

• Apply compost or FYM: 5–10 t/ha
• Mulch with organic material (rice straw, dry leaves)
• Incorporate green manures
• Earthworms eat bacteria in partially decomposed organic matter — they need the food chain, not just raw materials

Step 3: Keep Soil Moist

Earthworms move through soil by moisture gradients. They die when soil drops below wilting point. Mulching dramatically improves moisture retention and earthworm activity.

Step 4: Inoculate New Areas

If your fields have near-zero earthworms, natural recolonization from field edges can take years. Accelerate by:

• Collecting soil + organic matter from a worm-rich area (forest edge, old orchard)
• Spreading in moist patches under mulch in your field
• Or: Start a vermicompost bed, then spread finished castings with worms onto fields

Expected Recovery Timeline

Time	What to Expect
Year 1	Worm population stabilizes — no more decline
Year 2	3–5x increase in population near compost application areas
Year 3	Population spreads across field; tunneling visible
Year 5	Full recovery possible in severely degraded soil

Earthworm Species in India

Species	Behavior	Use
Eisenia fetida (Red wigglers)	Surface dweller, compost specialist	Vermicomposting
Perionyx excavatus (Indian Blue)	Common across India, heat-tolerant	Vermicomposting + field
Lumbricus terrestris	Deep burrower (native to Europe)	Less common in India
Local Pheretima species	Deep burrowers — create drainage	Field soil health

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Next: Humus Formation