Here's an example of a red crab:

While adult crabs are adapted to life on land, their eggs and larvae can only develop in water. That's why every October, the forest-dwelling red crabs make a roaring migration to the sea to lay eggs and reproduce. Each year, about 120 million red crabs crawl from the island's high rainforests to the lower coast, creating a spectacular spectacle of a mighty crab migration.

Extended information:

Crab Habits:

A small percentage of crabs grow and reproduce exclusively in freshwater, where they tend to dwell under rocks in mountain streams. There are also a few crabs such as the ground crab can adapt to land life, burrowing in moist mud holes, and migrate to the sea during the breeding period. Most crabs are omnivorous. Some crabs are carnivorous, such as the pike crab, which preys on fish, shrimp and mollusks. A few crabs, such as the stranded window crab, scrape or filter feed on algae and organic debris.

Culture Technology:

A suitable crab breeding site should have good water quality, sufficient water supply and easy drainage. To ensure good permeability, sandy or sandy loam land should be used. The depth of water in the pond is controlled at about 1m, and the shallowest place should not be lower than 10cm. built ponds, leaving a few mounds inside, planting reeds, wild rice, calamus and other aquatic plants. On the one hand, these aquatic plants are a good source of nutrients for crabs to eat. On the other hand, it is conducive to the consolidation of river embankment to avoid water leakage caused by digging holes.

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Baidu Encyclopedia - Crabs