C. elegans Plate Counting Methods
Visual density preset
Look at the plate under the dissecting scope and pick sparse, normal, or crowded. Fastest method, accurate to ±50% — good for routine maintenance decisions and stock chunking schedules.
Region-of-interest (ROI) count
Count worms in a defined area (typically a 1 cm2 square drawn on the plate bottom with a marker) and multiply by the total plate area. Accurate to ±20% for evenly populated plates.
Picking-based count
For high-precision experiments (lifespan, brood size), pick worms one by one to a count-only plate. Slow but exact. Use for any experiment where worm count matters at the individual level.
WormSizer / WormLab automated count
For high-throughput labs, image analysis software counts worms from plate scans. The accuracy is comparable to ROI counts but lets you process hundreds of plates per day.
Managing Plate Density
Plate density management is the single biggest determinant of stock health in C. elegans labs.
Why density matters
Above ~200 worms/cm2, the OP50 lawn cannot keep up with metabolic demand. Worms enter starvation, which triggers dauer formation in many strains. Once a plate goes into mass dauer, the cohort is unusable for most assays and the only recovery is to chunk the few non-dauer worms and re-establish.
Standard maintenance density
Aim for ~100 worms/cm2 as a maintenance target. This gives 2–3 days of buffer before food depletion and produces enough progeny for the next chunk.
Chunking strategy
Cut a 1 cm2 agar block from the densest part of the plate and transfer it to a fresh seeded plate. The worms migrate onto the new lawn within hours. Repeat every 2–3 days at 20 °C for active stocks, every 5–7 days at 15 °C for slower turnover.
