Hermit Crab
Coenobita spp.
Description
Hermit Crabs are small crustaceans known for their habit of inhabiting empty shells to protect their soft abdomen. They have a hard exoskeleton on the front of their body and are easily recognized by their distinctive behavior of constantly switching shells as they grow. Hermit Crabs are typically brown or tan with some species showing colorful patterns. These crabs are primarily nocturnal and are quite social, often seen in small groups. They are active scavengers, cleaning up leftover food, detritus, and algae in their environment.
Habitat Origin
Hermit Crabs are native to coastal regions, primarily found in tropical areas, including parts of the Caribbean, South America, and the Indo-Pacific.
Ideal Number
Ideal Number in Aquarium: 2-4 Hermit Crabs for a small tank; more if the tank is large enough, but they should be kept in groups to maintain natural social behavior.
Favorite Food:
Hermit Crabs are omnivores and will eat a variety of foods, including algae, detritus, small crustaceans, and leftover fish food. They also enjoy eating fruits and vegetables, such as lettuce, carrots, and zucchini. Providing calcium-rich foods like cuttlebone or crushed coral is important for shell health.
Behavior:
Hermit Crabs are peaceful but can be territorial over shells. They will often engage in a “shell battle” when competing for a larger shell as they grow. They are highly active and spend much of their time foraging for food and exploring their environment. Though nocturnal, they may be active during the day if they feel safe and secure.
Special Care:
These crabs need access to both dry and moist areas in the tank. Humidity levels should be high (around 70-80%), and the crabs should be provided with a shallow water dish for drinking and bathing. Shell selection is crucial for their health, so provide a variety of shells in different sizes. Marine species require saltwater, while freshwater species need appropriate freshwater setups.
Compatibility with Other Fish:
Yes, they can generally coexist peacefully with other non-aggressive species. Avoid keeping them with large, aggressive fish that may harm them or steal their shells. They can also coexist with other crustaceans and snails, but caution should be exercised to ensure they don’t compete for shells or food.
Breeding Tank Setup
A separate breeding tank is strongly recommended for hermit crabs to maintain optimal water conditions and protect the delicate larvae from predation. A 20-gallon (75-liter) tank is suitable for a small group, while a 30-gallon (115-liter) or larger setup is ideal for breeding multiple pairs or sustaining a larger colony. Hermit crabs require saltwater for reproduction, with stable parameters: a pH of 8.0–8.4, temperature between 24°C and 29°C, and specific gravity of 1.020–1.025. Use fine reef sand or aragonite as substrate, along with caves, coconut shells, or terracotta pots for shelter. A sponge filter or marine filter with gentle aeration is preferred to avoid strong currents. Lighting should be subdued, set to a natural 10–12 hour cycle to mimic their nocturnal environment.
Conditioning the Breeders
To prepare hermit crabs for breeding, offer a varied and nutritious diet over several weeks. This should include fresh fruits and vegetables (e.g., apples, leafy greens), protein sources (like boiled egg, fish, or shrimp), and marine foods such as krill or algae. Calcium supplements like crushed eggshell or cuttlebone are essential for molting and reproductive health. Weekly partial water changes (25–30%) are important for maintaining water quality, but always ensure new saltwater matches existing salinity and temperature to avoid stress.
Spawning Process
Hermit crabs spawn by releasing eggs into saltwater, where the larvae begin their planktonic life cycle. This usually occurs during warmer months, but can happen year-round in ideal tank conditions. Females carry thousands of eggs beneath their abdomen for 2–4 weeks before releasing them into the water. After this, separating the adults is not necessary, but transferring the larvae to a dedicated marine tank can significantly increase survival. This is especially important in tanks with predators or heavy water flow.
Larval Care
Once released, the eggs hatch into free-swimming larvae (zoea) that float in the water column. These larvae require microscopic live food such as marine plankton or rotifers, which can be cultured or purchased. They remain in this stage for several weeks, passing through multiple molts before settling. Water quality is critical: maintain stable salinity and temperature, and conduct daily water changes of 10–20%. Use a gentle filtration system that provides oxygen without pulling in the fragile larvae.
Breeding Tips
Hermit crabs typically reach reproductive maturity at 1–2 years of age. Males and females are hard to distinguish, though females tend to have broader abdomens for carrying eggs. Careful observation during mating may reveal differences in behavior and body shape. Avoid stressors such as sudden water parameter changes, overcrowding, or aggressive tank mates, as these can inhibit breeding or harm molting crabs and larvae. With stable conditions, patient monitoring, and gentle care, breeding hermit crabs in captivity becomes a rewarding challenge.