It's important to keep the eggs in a moist, but not wet environment. Never keep these eggs under water (this will drown the embryos)! Keep the temperature between 18 and 28°C (65-82°F). The higher the temperature, the faster the snails will hatch.
After 2-4 weeks (depending on the species and the temperature, 14 days at 25°C in the case of Pomacea canaliculata) the first little snails should appear. If they don't after 3 weeks, you can try to help the young snails.
If you don't see little snails after breaking a 4 weeks old clutch, it can be that the eggs aren't fertilised or that the air moisture was too low.
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