Geothelphusa dehaani (blue variant) “Sawagani”

Hello again!
These past few weeks have been quite busy, the combination of the flu and work doesn’t do the body any good. Nonetheless I am back, this time with a post on a freshwater crustacean called Geothelphusa dehaani (blue variant). They go by the name of “Sawagani” here in Japan.

Sexually mature male

This is a small freshwater crab that is found in and around the forest streams of Japan. They are quite abundant during the warmer times of the year, Spring and Summer, where many can be found crawling around out in the open, and there are baby crabs everywhere. As opposed to the colder times of the year (Fall, and especially Winter) they tend to “shutdown” and tend to go into “hibernation” you could call it. They do not breed, they aren’t found crawling out in the open, and basically just not active at all. Take the one male that I currently have in my terrarium. During the Summer when I first got him, he would crawl and climb all over the tank all day, very active. Yet now during the Winter, it has gotten very cold, and I never see him, he does not even eat the food I place in the tank, although he is still alive, he just always stays under the water and hidden.

In terms of sexual dimorphism, both males and females can exhibit the blue and white coloration, the brown colored specimens seem to be sexually immature. The easiest way to tell the difference between the sexes is the males have 1 large claw, and 1 smaller claw. Also the females have a larger/wider “flap” on their abdomen, in order to carry the eggs/babies.

Sexually immature specimen

In their natural habitat (given you collect them at the right times of the year, as stated above) you can find them crawling anywhere on the ground. Most of the time they can be found especially under rocks, it seems that, that is where they make their homes.

A blue variant excavating a home underneath rocks

They are very good climbers, in the forest I have seen them crawling steep rock faces. As for food, they like most crustaceans are scavengers. They have been documented as eating, rice, algae, bugs, other dead crustaceans, and vegetable matter (soy beans, bamboo root etc). I personally fed my crab cooked white rice! Seems odd, but he would go nuts for it!

An older blue variant male eating a piece of old carapace

A Red variant eating some vegetable matter

As far as I could tell, in terms of breeding, the females carry the eggs on their underbelly, and they carry them until the eggs hatch into baby crabs just under 1cm across, at which point the female drops them, and they’re left to fend for themselves.

Blue variant females carrying eggs
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Red female carrying babies that are soon-to-be dropped

Recently dropped juvenile
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Like I mentioned earlier this is the blue variant of Geothelphusa dehanni. There is another known variety that naturally occurs in Japan, and it is the red variety. The lifestyle and habitat of the red variety is no different from the blue variety.

Red variant male

I hope you all enjoyed this post on my most recent pet, Geothelphusa dehaani! Please leave a comment if you like what you are seeing, it would be much appreciated!
Take care all!