The sand bubbler crab is one of the cutest species you can find on the beach. These crabs are so tiny you might step on one without realizing it. You can easily spot them by their tiny patterns of balls and their burrows on the beach.
In this blog, I will discuss various aspects of these little crustaceans, including some incredible facts that you may not have known before.
Quick overview of sand bubbler crab
- Common name: Sand bubbler crab, bubble crab
- Scientific name: Family — Dotillidae
- Lifespan: Up to 5 years
- Color: Blue: Orange
- Size: 1.2 cm
Sand bubbler crab facts
Where do sand bubbler crabs live? (Habitat/Location)
Sand bubbler crabs thrive across sandy beaches and estuaries in tropical and subtropical regions of the Indo-Pacific. Found in countries like Iran along the Persian Gulf coast, Myanmar, Thailand, Cambodia, Australia, Japan, and Hong Kong, they adapt well to areas exposed to waves and sheltered shores.
These crabs inhabit sandy and muddy shores, including mangrove environments, with a notable presence along the Bay of Bengal. Their adaptability allows them to survive in varied coastal settings, making them an integral part of these ecosystems across the Indo-Pacific.
Sand bubbler crab species
Crabs that make sand balls belong to 2 genera, Scopimera and Dotilla, from the family Dotillidae. All of the species are from these two genera. Here are some species I found, along with their habitats:
- Scopimera crabricauda — Persian Gulf coast in Iran
- Scopimera inflata — Sand bubbler crab endemic to Australia
- Scopimera globosa — Japan
- Scopimera intermedia — Hong Kong
- Scopimera philiptwo — China, Japan, Korea, Taiwan
- Scopimera sheni — Philippines
- Scopimera longidactyla — China, Korea, and Taiwan
- Dotilla sulcata
- Dotilla fenestrata — East Africa
- Dotilla fenestrata — Kenya
- Dotilla intermedia — Thailand
- Dotilla wichmanni
Why do sand bubbler crabs make patterns/balls of sand?
Crab sand balls – Sand bubbler crabs make little sand balls as they feed on food particles (meiofauna) coating sand grains. The crabs scoop up sand with their pincers, eat the particles, and roll the leftover sand into balls randomly. By making these sand balls, the crabs ensure that they do not eat leftover sand twice at the same time. Occasionally, these sand balls end up forming intriguing patterns like animals, flowers, mazes, and even galaxies.
They do it during low tide; once high tide returns, they retreat to their burrows, where they wait for the tide to recede and fresh sand that has been enhanced by washed-up meiofauna to be ready. Once the high tide subsides, they emerge from their burrow to participate in the daily cycle of sand bubbling.
Appearance of sand bubble crab
The sand bubbler crab has a distinct look, blending in with its sandy environment thanks to its natural sand-like coloring. Its body shows subtle hues of blue and orange, adding a slight pop of color that contrasts with its surroundings. This tiny crab, which can grow up to 1.2 cm in size, stands out due to its unique long pincers and hairy legs that assist in its daily activities of digging and feeding on the beach.
Behavior of sand bubblers
What do sand bubbler crabs do? Sand bubbler crabs have unique behaviors that help them survive in their coastal environments. Males are known to perform a funny, yet assertive, dance to show dominance. They straighten their legs, stand tall, and stretch their claws high above their body before quickly pulling back into attack mode. Larger crabs or burrow owners usually win these territorial disputes. Some crabs move in groups during low tide, while others prefer to remain in their burrows; however, not all of them stay in a single burrow for an extended period.
Unique breathing: Sand bubbler crabs breathe from air through membranes located on their legs, not with gills like most of the crabs. The membranes resemble windows on their legs; that’s the reason behind their scientific name, Scopimera, which means “thighs with windows.”
They face threats from birds, larger crabs, and even other sand bubblers, with red-capped plovers being a common predator. Interestingly, unlike most crabs, sand bubblers move forward in straight lines and often emerge in large groups. Females and smaller crabs tend to stay closer to the water, where food is better and competition is less, while males occupy more inland areas, though both groups maintain similar body conditions.
During the cooler season, sand bubblers slow down and forage in smaller areas, likely due to colder temperatures. Despite frequent disturbances like human activity or predators, they don’t show significant changes in behavior after repeated challenges1, demonstrating their adaptability. Recruits, or new crabs, tend to appear in summer, contributing to the colony’s growth.
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Mating and reproduction of sand bubblers
They engage in a unique mating ritual. Males venture out from their burrows to attract resident females, moving gracefully around their homes. When a wandering female catches a male’s eye, he chases her down, bringing her to his burrow and sealing the entrance for privacy.
However, many of these females aren’t ready to spawn and may leave after a few days. Only about 30% end up laying eggs after mating. Males may fight for their chance; the last male to mate with a female often has the upper hand, as his sperm will fertilize most of the eggs.2
Sand bubbler crabs reproduce year-round, with males showing three stages of gonad development and females having five stages. Females ready to release eggs prefer water-saturated areas, while those still carrying eggs stay near burrows.
Mating and egg-laying occur inside burrows, where males dominate. Interestingly, the size at which both males and females reach maturity is around 2 mm. Males often remain in burrow zones, but more females can be found in water-saturated areas during egg-laying. These crabs’ reproductive strategy and year-round activity ensure high reproductive success across their populations.
Sand bubbler crab as a pet
To keep a pet crab, you need to create an environment that replicates their natural habitat. One challenge with keeping this crab as a pet is that replicating its unique feeding method in captivity can be difficult. If you can’t mimic their wild habitat and feed them like other crabs, they won’t survive for long. If you are interested in petting them, here is a forum conversation that might be helpful.
#Faqs
Are sand bubbler crabs dangerous?
They are harmless to humans, as they don’t pinch/bite.
Can you eat sand bubbler crab?
They are too small; they barely have meat on their claws. Also, they increase the beauty of the shore, so I wouldn’t recommend eating them. [toxicity is unknown]
What are the little balls of sand on the beach?
Those little balls are created by sand bubbler crabs as part of their feeding process.
Do crabs eat sand? What do sand bubbler crabs eat?
No, crabs don’t eat sand. Sand bubbler crabs feed on tiny food particles, like plankton and organic matter, that coat sand grains. They scoop up sand with their pincers, filter out the edible bits, and discard the rest by forming little sand balls.
Why do sand bubbler crabs make sand balls? Why do crabs make little balls of sand?
Sand bubbler crabs make tiny balls of sand while feeding. After filtering out food, they roll the leftover sand into balls to avoid rechecking the same grains. These balls often scatter in patterns across the beach, especially during low tide.
Why do crabs make sand balls? Why do crabs bubble? Why crabs make bubbles?
Crabs make sand balls while eating, not for fun. As for bubbling, crabs often blow bubbles around their mouthparts to help keep their gills moist when out of water. It’s part of how they breathe in air temporarily while on land.
What are the tiny crabs on the beach?
The tiny crabs you see on the beach making little sand balls are likely sand bubbler crabs. They’re only about 1 cm in size and known for their adorable sand art during low tide.
Many thanks! 😊