Blue Spider Crab – Detailed Guide: Care, Tank Setup, and Facts – petacrab
The blue spider crab, an aggressive colored semi terrestrial crab, is a great addition to the paludarium. But it is a rare species in Southeast Asia and lives in mangroves. This crab is quite new to the hobby, and little is discovered about them. That’s why you may have difficulties finding information about them.
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This crab is quite simple to take care of because it is a semi-terrestrial, peaceful crab. So let’s dive into the world of pet blue spider crabs.
| Name | Blue spider crab, mangrove crab |
| Scientific name | Neosarmatium rotundifrons |
| Size | Up to 7 cm |
| Care level | Easy |
| Breeding | difficult, but possible |
| Color | Purple, blue, and white |
| Distribution | Philippines, Samoa, Nias, Java, Moluccas, Australia and Taiwan |
| Habitat type | Paludarium/Terrarium |
| Water type | brackish |
| Temparament | Peaceful |
| Optimal temperature | 24°C to 30°C |
| Diet | Omnivore |
| Sleeping nature | Nocturnal |
| Life span | 2-3 years (based on similar species) |
- Kingdom: Animalia
- Phylum: Arthropoda
- Class: Malacostraca
- Order: Decapoda
- Family: Sesarmidae
- Genus: Neosarmatium
- Species: Neosarmatium rotundifrons
- Appearance: The shell, or carapace, of the blue spider crab is smooth and shiny, with tiny pits and small tufts of hair. The edges of its shell have a wavy design, with a prominent tooth-like bump near the top and a smaller one next to it. The front of the shell also has a wavy look, featuring a deep notch in the center. They have a beautiful purple to blue color with white gradation, which indicates their name.
The crab’s claws are also unique. They have a noticeable ridge running vertically on the inner side and a shorter ridge on the outer side. The top part of the claw has 4–5 evenly spaced spikes.
The males are larger and more colorful compared to females.
- Scientific name: The original name was considered Sesarma rotundifrons, but its current name is Neosarmatium rotundifrons. But the fun fact is that Sarmatium fryatti (given by Tesch in 1917) is now considered to be the same species as Neosarmatium rotundifrons.1
You can choose a 10 gallon tank for a pair of males and females. Choose 20 gallon if there is a group of blue spider crabs and increase the size if there are tankmates, ensuring the paludarium is not overcrowded.
As they are peaceful crabs, they won’t fight with tankmates, but they may become territorial and show aggression if there is not much space.
Don’t forget to close the tank with a glass lid or they may try to escape, as they are great climbers.
If you previously owned a semi terrestrial crab, you may know how to set up a proper paludarium. If you are new at this, here is the guide-
Take a good substrate and fill the tank with it, The substrate should be at least twice as deep as the tallest crab of the group because they will burrow and make tunnels under the substrate.
Now make a space for water; the water and substrate ratio should be 1:4. In essence, they require more land than water and make sure they can leave the water with ease.
Prefer sand for the main part of the substrate, then mix it with some soil and a little amount of gravel. This will mimic their wild substrate (mangrove) as well as help hold humidity and help the crabs’ tunnel keep its shape.
You can mix commercial substrate bio stratum and aqua sugar white sand, which can be found in online stores
Pour the water area with brackish water and keep a freshwater bowl at the corner of the tank.
You can keep only freshwater, but brackish water is what they need.
Make a hideout with some cool things; there are different kinds of caves that can be found in online stores, like mossy caves or half log pipes. A minimum of one hiding place for one crab will ensure there is no territorial dispute.
Spread some pebbles over the substrate. You can also use rocks to make hiding places, but woody caves and materials will be better as they live in areas with no rocks.
You can use some plants, like radiator plant, common asparagus ferns, Tillandsia, and baby tears. Use some moss, such as cushion moss, hypnum moss, and fern moss. Ensure the roots of the plants don’t spread too much, which blocks the way of digging.
Add one or two climbing mediums with rocks or spider wood.
The temperature for blue spider crab should be between 24°C and 30°C. Try to keep the temperature between 25°C and 26°C and track the temperature with a thermometer.
The blue spider crab will need high humidity to thrive, try to keep it above 75% and below 85%; a slight change in humidity won’t be a problem. The water and the plants should be enough for humidity, however, keep track with a hygrometer. Use a humidifier if needed.
Closed or nearly closed paludarium helps maintain humidity and temperature.
Being omnivores, blue spider crabs will eat whatever their hands get off. Start with dried shrimp, krill, brine shrimp, mysis, and blood worms. Gradually, you can give them vegetables, such as broccoli, spinach, and cucumber; consider dried leaves or leafy vegetables like kale.
Try giving them fish food, wet cat food, turtle food, pellets or fish flakes.