Japanese freshwater crab
Amazing fact
When it rains, the Japanese freshwater crab may walk on land away from the water.
国土交通省 九州地方整備局 筑後川河川事務所
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An illustration based on the real animal.
A little discovery to share.
When it rains, the Japanese freshwater crab may walk on land away from the water.
THE REAL WORLD
The real Japanese freshwater crab
- Scientific name
- Geothelphusa dehaani
- Japanese name
- サワガニ
- Group
- Freshwater animals
- Class
- Malacostraca
- Order
- Decapoda
- Family
- Potamidae
- Genus
- Geothelphusa
A crab found nowhere but Japan; it spends its whole life in fresh water such as streams.
Unlike other crabs, its babies are born looking like tiny adults, and they cling to their mother's belly for a while as they grow.
Depending on the area, the shell color differs: some are reddish and some are bluish.
How the Japanese freshwater crab lives
During the day, it hides between stones or under fallen leaves. At night, it becomes active and feeds. It eats algae, water plants, aquatic insects, earthworms and fish. It spends winter in a hole dug under a damp rock or a similar spot a little away from the water.
国土交通省 九州地方整備局 筑後川河川事務所Basic data
- Size
- Carapace length: about 30 mm
- Diet
- Small aquatic animals and plants such as algae
- Range
- Japan (Honshu, Shikoku, and Kyushu)
Where the Japanese freshwater crab has been recorded
Records: GBIF.org (CC0 and CC BY 4.0 records, retrieved 2026-11-07). Map: Natural EarthSee the records on GBIF
Watch wild animals from a distance. Do not touch or feed them, and take care of the places where they live.
Names around the world
Names come from Wikidata and iNaturalist records. Where a language has no recorded name, we use the scientific name.
Sources and how we check
- 井の頭自然文化園 — サワガニChecked: 2026-11-03
- 国土交通省 九州地方整備局 筑後川河川事務所 — 底生動物 サワガニChecked: 2026-11-06
We check each fact against its source. The illustrations simplify how the real animal looks.
The classification (class, order, family, genus) follows Wikidata records, checked against GBIF. Classifications can change as research goes on.
The basic data are the values given in each source. They vary with how the animal is measured, whether it is male or female, and whether it lives in the wild or in captivity.
This page was translated from the original Japanese with the help of AI.
Report a mistakeWhen you meet the Japanese freshwater crab, look for this
- Look at its smooth shell, which is wider toward the front.
Animals do different things from day to day, so you may not always see this.
国土交通省 九州地方整備局 筑後川河川事務所EXHIBIT INFORMATION
Places that keep or show the Japanese freshwater crab
Zoos, aquariums and other places whose official websites say they keep or show this animal.
Kanto
Displays can change with the animals’ health and the seasons. Check each facility’s official website before you go.
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Others in Decapoda
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