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Today on Animal Fact Files we’re discussing potamon crabs. These freshwater crabs range throughout the Middle East, northern Africa, and southern Europe. In fact, they’re some of the only living species of freshwater crabs found in Europe and they’re sometimes referred to as European freshwater crabs. Of course, that’s a bit of a misnomer since their range exceeds this. They’ve undergone a lot of taxonomic changes over the years, so it’s difficult to say how many species are definitively classified in the Potamon genus today. Plus, they’re relatively understudied, so there may be species yet to be discovered. Broadly speaking, there are a few dozen species of these crustaceans. They live in fragmented populations across their range, so it’s possible that some species that are currently listed as a single species may actually be many species that simply haven’t been fully studied. This is important to note for later, so keep this in mind moving forward.

Potamon crabs are considered “true” freshwater crabs because they don’t tolerate saltwater. They can’t live in the sea. They live in streams, rivers, lakes, ditches, and other freshwater systems throughout their range. These arthropods are typically bottom dwellers, meaning they’re benetic animals. They may be found on shallow mud which they can burrow into, rocks which they can crawl under, or submerged plants which help disguise them as they move about. Potamon crabs are listed as both nocturnal and diurnal, so they may be active during either the day or night depending on environmental factors. Human disturbance may encourage them into a nightly routine while being larger in size may help them feel brave enough to face the daylight. These crabs only reach 3 inches (76 mm) wide on average, but this size still gets them commonly referred to as “large” crabs. The largest individuals can nearly double this in size, although these are rare.

Potamon crabs search for food in all forms. Like many crab species, these invertebrates eat pretty much anything they can sink their claws into including worms, insect larvae, molluscs, tadpoles and frog eggs, fish and their eggs, as well as plant material and decaying matter. They’ll even eat their own molted shell! It’s a great way to recycle nutrients into their body. They’re typically brown in appearance which may help them blend in with their surroundings, but it’s likely they’re eaten by a myriad of larger animals including mammals and wading birds. What’s more, they’re threatened by habitat loss and pollution. Remember how we mentioned they have fragmented populations? This is important because it’s possible these separated populations are actually separate species, which could mean that the loss of a population could actually mean the loss of an entire species. That being said, there are some Potamon crab species listed as Near Threatened simply due to the anthropogenic threats they face.

There’s little information on the mating habits of these animals, however, at least one species prefers to keep their mating and egg-rearing during the warmest months of the year. Females are wider than males to accommodate their eggs, but overall smaller than males. It’s believed the males being larger than the females help facilitate their ability to mate– it makes things easier for them, so the largest males have the best chance of passing on their genes. Female potamon crabs produce about 100 eggs at a time and these are brooded, held under the female’s abdomen while they develop over the course of a month. The babies hatch looking like small versions of the adults and even after hatching, the babies remain with their mother for almost another week, growing while still under her protection. It’s unknown how long these crustaceans live in the wild, but some owners suggest they can live about 5 years in captivity.

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