Thai Micro Crab (Limnopilos naiyanetri)

Thai Micro Crab– Detailed Guide: Care, Diet, and Breeding

by Michael

Looking to add some variety to your shrimp habitat, or maybe you just want a change of pace in your community tank? In this detailed guide, I have compiled everything you need to know about caring for Thai Micro crab.

Thai Micro Crabs are a great choice for many small aquarium set ups. These interesting little crabs live up to their micro name and they’re about as friendly as a crab can get. They are also known and sold as Limnopilos naiyanetri, Pill-box crabs and the False Spider crabs.

Actually, I would like to say one thing before I start. Generally, in all my guides you can find a lot of references to official studies and researches. The point is that I want to provide as much information as I can for everyone who reads them.

This time it was a challenge. Limnopilos crabs have generally been poorly studied and detailed information about their biology, ecology, and ethology is not available including information about their reproduction.

Freshwater crabs of the genus Limnopilos were discovered in Thailand by hobby aquarists and introduced on the Germany market in 2008.  Literally, our hobby is almost ahead of science. We keep species, which have not been fully studied yet. 

Quick Notes about Thai Micro crab

Name Thai Micro crab
Other Names
Thai Micro Spider crab, False Spider crab, Micro crab, Freshwater Spider Crab, Laos Micro Spider Crab, Pill-box crab
Scientific Name Limnopilos naiyanetri
Tank size (optimal) 5 gallons (~20 liters)
Keeping Medium
Breeding Very Difficult 
Size Carapace – 1 cm (0.4 inches); 2.5 cm (1 inch) across the leg span
Optimal Temperature 22 – 27°C  (~70°F – 80°F)
Water type Freshwater
Optimal PH 6.5 – 7.5
Optimal KH 2 – 6
Optimal GH 4 – 15
Optimal TDS 120 – 180 (100-300)
Nitrate Less than 20 ppm
Diet Detritivore /omnivore
Temperament Peaceful
Life span up to 1 – 1.5 years
Color Form Pale transparent to brownish grey

Basic Information about Thai Micro crab   

Thai Micro Crab is a freshwater crab and can spend their entire lives underwater. It makes them one of the few fully aquatic crabs in the world.

They are native to Thailand. As of now, they have only been found to exist in one specific river (the Tha Chin River, Nakhon Chai Si District, of the Nakhon Pathom Province, in Thailand) where they inhabit the roots of water plants (hyacinths).

They are a very recent addition to the aquarium hobby. Their newness to the hobby and their lack of habitat diversity makes them relatively rare to find in pet stores and online.

Fact: The species is named in honor of Professor Phaibul Naiyanetr of the Department of Biology, Chulalongkom University, Bangkok, Thailand.

Fact #2: The genus Limnopilos (family Hymenosomatidae) was scientifically described in 1991, later synonymized with genus Hymenicoides, and in 2007 resurrected as Limnopilos because several distinctive characters were identified.

Description of Thai Micro Crab

Micro crabs are not especially colorful. Generally, Thai Micro Crabs are brownish-grey (pale transparent) in color. However, their color can also range from a sort of brownish-orange color to a light gray. Some aquarists say that these crabs can change the hue of the collar, depending on the mood.

Thai Micro Crabs have long thin legs and their entire body, including their legs and claws, are covered in small bristles. They use these bristles to catch food particles (including its own pelagic offspring) by filtering water through them. These tiny crabs appear almost spider-like, due to their long leg span and small bodies.

Note: The genus name Limnopilos is an arbitrary combination of letters with a vague reference to the fact that the animals of this genus inhabit freshwater and are hairy.

Adult Size of Thai Micro Crab

Full-grown, an adult Thai Micro crab’s shell (carapace width) is only around 1 cm long (less than half an inch). Their thin, spindly legs will only span up to about 1 inch (~2.5 cm). At first glance, they almost appear more like underwater spiders than crabs.

This is the largest they can get. Species of the family Hymenosomatidae are the smallest freshwater crabs in the world. 

Lifespan of Thai Micro Crab

These crabs are new to the aquarium hobby, so their lifespan in their native habitat is not well documented. However, in captivity, the life span of healthy individuals is 1 – 1.5 years. You can expect to have your Thai micro crabs for at least this long, or longer depending on how well you care for them.

Thai Micro Crab Behavior    

Thai Micro crabs are shy, docile creatures and usually came out only at night. They spend their entire lives underwater, never breaching the surface. They prefer to spend their time hiding amongst aquarium decorations, often in the most biologically dense areas of the tank (areas with a high density of algae and other food sources).

The crabs are peaceful and can easily be kept in groups. They are social crabs. Unlike other crab species, they are not territorial and males will not fight. Thai Micro crabs will often share a hiding place, it is not uncommon to see many of them in the same areas. 

When threatened, or startled Thai Micro crabs will do their best to escape, or take cover. They are entirely defenseless. Thai Micro Spider Crabs are generally non-aggressive, and many aquarists keep them perfectly safely alongside adult shrimps and snails.

Micro crabs are not an especially or highly active species of crab. But, that does not mean they aren’t a lot of fun to keep. Their spider-like appearance and unique acrobatic habits make up for their lack of size and flashy colors. Sometimes they can be seen, filtering food along the bottom of the tank, or moving from one area to another.

Thai Micro crabs are totally safe with plants. These crabs are absolutely fully aquatic and not prone to escaping.

Thai Micro Crab – Male and Female Difference

Sexing Thai Micro crab is not easy because of their tiny size and fragility. Males and females are very similar in color and appearance there is one nearly foolproof way of determining gender. Examination of the flap at the bottom with a strong magnifying glass is the surest way. The females have a wider flap at the bottom, while males have a narrow, tapered appearance.

Non-sexual features similar to the male, chelipeds as swollen as that in males but smaller; dentition and setation similar. Abdomen 6-segmented, all intersegmental sutures distinct and articulating, lateral edges of segments 3-6 lined with setae; segment 6 truncated, proximal half of lateral edge concave, tuft of setae at tip.

Thai Micro Crab Molting    

Thai micro crabs don’t molt as often as other crab species, mostly because of their small adult size and slow growth rate. However, when they do molt, the process is much the same as other crab species.

They begin the molting process by filling their carapace with water. This water is used to separate and crack open their exoskeleton. Over the molting process time period, they will emerge from their carapace as a new one forms beneath it.

After molting their bodies will be soft and still mostly comprised of water. It is not uncommon for them to appear almost translucent. Their bodies will slowly harden over the next few days and you may find their old, shed skeleton among the aquarium decor.

Molting is a time when your Thai Micro crab will be under a lot of stress and very susceptible to injury. I do not recommend invasive tank cleaning, or rearranging during this time. It is not uncommon for a molting crab to go into hiding and not reappear until he is finished.

Keeping Thai Micro Crab    

Thai Micro crabs are relatively easy to take care of. The tank requirements of these crabs is very similar to that of dwarf shrimp. To be exactly, they require the same water parameters as Crystal shrimp.

They need a freshwater tank, with a pH of 6.5 – 7.2. Their temperature requirements aren’t very demanding and in warmer areas, a heater may not be necessary. Their water temperature should be maintained and kept between 21 – 27C (70 and 82 F). Your Thai Micro crabs will begin to suffer if their water temperature gets too high, or too low, or fluctuates rapidly.

Read my guide “Crystal Red Shrimp – Detailed Guide: Care, Diet and Breeding”.

However, if you have harder water and keep Neocaridina shrimp (for example, Cherry shrimp, etc), Thai Micro crabs will accept these water perimeter. These crabs adapt well to aquarium life.

Tip: Look at night and you will likely find them. They come out very quickly after lights off. If you want to see their nocturnal activities you can buy a Night Glo bulb (Link to check the price) or similar bulb.

Before you put Thai Micro crabs in the tank, make sure that the aquarium is well cycled and have had time to properly mature. Do not forget that they need careful acclimation (read more about it here) as all invertebrates. 

A close eye should be kept on the water values at all times. Do regular water tests using a test kit (link to check the price on Amazon) and perform regular water changes.

For more information you can read my articles:

– “How to Do and How Often to Do Water Change in Shrimp Aquarium”.
“Best Aquarium Test Kit”.

Thai Micro Crab and Tank Size

A large tank is not needed for these tiny invertebrates. Even more, in large tanks, there is a big chance that you will never see them again unless they dare to come out in the daytime. That is why Thai Micro crabs are an excellent choice for small Nano tanks.

A colony of up to 5 – 6 Micro crabs can be kept in tanks as small as 5 gallons, as long as the water is filtered appropriately. Adequate filtration is very important no matter the tank size.

You may find you have better luck with a slightly larger aquarium setup however. Thai micro crabs are very sensitive to poor water conditions, adequate filtration is very important no matter the tank size.

Thai Micro Crab, Plants, Substrate Decorations, etc.

These crabs aren’t too particular about the substrate in an aquarium. They spend most of their time hidden in nooks and crevices, or in other decorations amongst the tank. Choose any shrimp compatible substrate you enjoy, however choosing a color that contrasts their greyish-brown bodies will make these creatures a lot easier to spot.

They enjoy planted tanks with lots of vegetation to cling to. Decorations, fake, or real aquarium plants and lots of places to hide will be greatly appreciated by your Micro crabs. In their natural habitat, they spend most of their lives hiding in the roots of floating freshwater plants, like the water hyacinth. Their natural behavior is to be a bit reclusive.

They do not I really like the bright light. Ideally, they should have a dark corner to get around in. So in your aquarium, it’s really important to provide them with spaces that they can hang out and feel secure.

Tip: Be extremely careful when you use a net with them. Thai Micro crabs are very fragile. It is very hard to handle them without ripping off their legs or do any damage. Yes, the lost limbs will regrow after a molt or two but there is no need to harm and stress them anyway.

Thai Micro crabs particularly seem to appreciate fairly dense plants that provide them cover and a place to hide. For example, Mosses are also great additions to their tank. Plants, such as Anubias or Java Fern, are also a great choice as the crabs like to hang out on the long roots. (Read my article “Top 5 Plants for Your Shrimp Tank”).

Note: Besides water parameters and temperature, the key to their success is a high bubble output at the surface of the tank.

Tank Equipment (links to check the price on Amazon)

Regarding filtration, I would recommend a Matten filter (or any other similar). Sponge Filters or Matten Filters are the best types of filtration because the crabs graze on the porous sponge. They love that texture.

You can read my articles to learn more about it

The Best Filtration System for Breeding Shrimp”.
– “Best Remineralazers for Shrimp Tank“.
– “Best RO/DI systems for Shrimp tank“.
– “Top 5 Substrates For Planted Aquariums“.

Feeding Your Thai Micro Crab    

Thai micro crabs are omnivorous scavengers by nature. They do not actively hunt, but they will eat just about anything edible. They are a non-aggressive species that acquire most of their food through using their bristles to filter food pieces, like microorganisms from the water with the tiny bristles on their body. These particles are then eaten as the crab cleans himself.

They also collect food from the ground, between the floating plants and graze on algae wafers and blanched vegetables too.

Read my article “How to Blanch Сucumbers and Zucchini for Shrimp, Snails and Fish the Right Way”.

Note: Thai Micro crabs are from the river. Therefore, they are used to water flow and handle the currents extremely well. Even more, because they partially filter feed, much like Bamboo shrimp (read more about it), they stay more active near the flow, they rest and eat off it. Therefore, it would be ideal to provide some in their tank.

In established aquariums, very little feeding is needed as the crabs forage and find plenty to eat around the tank (quite similar to any dwarf shrimp behavior). If you are planning to keep them with dwarf shrimp, you can feed them the same food.  The only problem is that dwarf shrimp will outcompete Thai Micro crabs in a tank. They are simply faster and bolder.

Thai Micro crabs can eat wafers, pellets, flakes, sinking commercial crab food, algae, biofilm, etc. However, according to some observations, they really prefer high fat, high protein powder diet (for example, Shrimp King – Baby Food and GlasGarten Bacter AE – links to check the price on Amazon). According to observations, Thai Micro crabs also like to eat daphnia (water fleas).

Crabs need calcium. I highly recommend reading my article “How to Supplement Shrimp and Snails with Calcium”.

Breeding Thai Micro Crab    

Thai Micro crab is definitely a challenge to breed.  Unfortunately, their breeding is still unsuccessful in captivity. While some hobbyists have reported hatched eggs and even formed, living baby crabs, there have been no documented reports of surviving offspring. Various keepers have failed to raise these crabs beyond the 9th day after the larvae hatched. Therefore, it is possible that their ideal breeding water parameters have not yet been figured out.

Very little is actually known about the life cycle requirements and husbandry rituals of these tiny crabs.

Here is all the information regarding the breeding process I could find.

Thai Micro crabs are fertilized internally; with the modified first pair of the male pleopods (the gonopods) transferring sperm into the female reproductive apparatus.

After mating, a female Thai Micro crab holds the egg cluster under her pleon. It is very hard to see the eggs. Reports suggest that the female occasionally opens its abdominal apron, but usually it is completely closed, so the eggs can only be seen through the transparent pleon.

Their eggs are orange at the start of development, then they become yellow before finally turning grey. Limnopilos naiyanetri have relatively large eggs. Their size is about 0.5 to 0.7mm in diameter and are carried under the female’s pleon until the larvae (zoea) hatch.

The incubation period lasts several weeks after that the mother releases around 70 larvae. This crab species is one of the rare reproductive types of freshwater larvae. Thai Micro crab larvae do not undergo brackish or seawater period.

Upon hatching the larva continue to be held. It is unclear at what point the female crab releases her offspring, however, they are not released while in larval form. Instances of early release have been noted, in which the larva quickly became food for the adult micro crabs.

The larvae of Thai Micro crab always move towards the light. So a permanent source of overtank lighting is essential when breeding to provide the offspring with orientation when swimming around.

Important: The larvae should have a lot of algae and biofilm in the tank.

Note: If you have HOB or canister filter, it also requires an extra pre-filter in the form of a sponge to prevent baby crab from being sucked in.

Tankmates Thai Micro Crabs with Other Aquatic animals    

Thai micro crabs, like many dwarf shrimp species, are social and nonaggressive. They enjoy the company of their own kind and should always be kept in colonies of at least 5 – 6. Larger colonies can easily be kept in larger tank set ups. Having a colony allows your micro crab to feel safe and secure. Larger colonies often have more active members, that can be seen venturing out from hiding and showing off more often.

Thai Micro crabs are very peaceful and due to their small size, they are practically defenseless. Because of this, they are only suited to the most docile environments. They are an easy snack for just about any predator, even some species of small fish. Thai Micro crabs should not be kept with other species of crab.

They get along great with just about everybody that is their same size and temper.

Good Tank Mates:   

  • Dwarf Shrimp (Neocaridina and Caridina species).
  • Filter shrimp (Bamboo shrimp and Vampire shrimp).
  • All kinds of snails.
  • Otocinclus fish.

Note: Because of their feeding technique, they may predate on tiny baby shrimplets and very young snails. They are totally safe with plants.

Bad Tank Mates: 

  • Larger or aggressive fish.
  • Any Crayfish species.
  • Other crab species.
  • Basically, anything that might decide crab legs sound good.

You can read my article “Сherry Shrimp in a Community Tank. Tips to Make it Successful”. The same principles you can apply for Thai Micro crabs.

Conclusion

Thai Micro Spider crabs should be kept in a small aquarium simply for visibility. These interesting little crabs live up to their micro name. If you put them in anything big they just “disappear”.

Even though they have attracted the attention of traders and keepers, the presented information about their life requirements is confused in many aspects. The species identification is not easy even for crustacean experts.

Thai Micro Spider crabs are generally considered interesting additions to an aquarium, but information about their living requirements are scarce.

Read more about freshwater crabs species in my article “7 Freshwater Crabs For The Tank”.

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