How to Separate Earthworms and Cocoons from Fine Castings During Machine Sieving

Every kilo of worms that leaves in a compost bag is breeding stock you paid for. Recovering worms and cocoons during screening is not a refinement — it is the difference between buying worms once and buying them repeatedly.

Start before the machine: let the worms move down

Worms avoid light and dry surfaces. If you stop watering a bed a day or two before harvest and remove material in layers from the top, the worms migrate downward ahead of you. The upper material you lift is then largely castings, and the concentration of live worms in what you feed to the machine is already much lower.

Screen at the right moisture

Screening very wet material makes recovery harder, because castings cling to worms and cocoons. Working at the normal 25–30% range keeps material loose enough to separate cleanly. Grinding ahead of the screen breaks the clods that would otherwise trap cocoons and carry them into the fine fraction.

Use the coarse fraction as your recovery stream

During screening, worms and cocoons behave like oversize: they do not pass a 3 mm or 5 mm opening and travel across the mesh into the coarse outlet. Treat that coarse stream as a recovery stream, not as reject. Collect it into a shaded container rather than leaving it in the sun, and return it to the beds the same day.

• Keep the coarse collection point shaded and out of direct sun.
• Return recovered material to the beds the same day, not at the end of the week.
• Cocoons are small, pale and easily missed — do not sieve the coarse fraction again to 'clean' it.
• Feed the machine at a steady rate; surging pushes material through faster than it can separate.

Where the machine helps

Because each mesh is set at a precise angle with two wipers pushing material back across it, material is presented to the openings properly instead of racing off the deck. Fine castings drop through and the worms and cocoons stay on top and travel to the coarse outlet, which is exactly the separation you want.

Frequently asked questions

Will a screening machine kill my earthworms?

Handled properly, no. Harvest so worms migrate downward first, screen at normal moisture, and collect the coarse fraction — which carries most live worms and cocoons — into shade for same-day return to the beds.

How do I avoid losing cocoons in the finished compost?

Cocoons behave like oversize and leave with the coarse fraction, so treat that stream as recovery rather than reject, and avoid re-sieving it to clean it up.