Ever spotted a little ball of fuzz hitching a ride on your live rock? Chances are, you’ve just met the Teddy Bear Crab (Pilumnus vespertilio). These tiny, fluffy critters often sneak their way into saltwater tanks, surprising aquarists with their teddy bear-like appearance. But don’t be fooled by the cuteness—these little guys can be quite the troublemakers!
Whether you’re wondering if a Teddy Bear Crab would be a fun addition to your tank or you’ve just discovered one hiding among your corals, this guide covers everything you need to know. From tank setup and feeding tips to their quirky behavior and breeding habits, let’s dive in and get to know these adorable yet sneaky crabs a little better!
Quick overview of teddy bear crab
- Scientific name: Pilumnus vespertilio
- Common names: Teddy bear crab, Hairy Crab, Bad Hair Day Crab
- Reef safe: No
- Diet: Carnivore
- Temperament: Semi-aggressive
- LIfespan: up to 15 years
- Size: 3-5 cm
- Sleeping nature: nocturnal
- Habitat type: saltwater aquarium
- Color: Brown
- Temperature: 70-80°F (21-26°C)
Habitat and distribution
You’ll find teddy bear crab in tropical, subtropical, and temperate waters across the globe, from the French Polynesian and Madagascar to Mauritius, Mayotte, and even the Red Sea.
These crabs are shy and quick to retreat into crevices when they feel threatened. Though mostly active at night, they emerge to forage and play an essential role in their ecosystem. They help with nutrients cycling by grazing algae and breaking down organic matter, boosting the health of their intertidal habitats. If you’re searching during the day, low tide about 10–15 cm might be your best bet. Keep in mind, though, that finding them in daylight can be tricky as they stay hidden.
Their distribution is pretty broad, covering areas across the Old World and Oceania. This means if you’re exploring these regions, you might get lucky enough to spot one, especially if you venture into places exposed to water surges where they like to dwell.
Some interesting facts about teddy bear crab
This small, unique crab (Pilumnus vespertilio) belongs to the Xanthidae family, where the other two hitchhikers, gorilla crab and gall crab, belong.
It has an endearing way of protecting itself. Known for its clever use of anemones, it holds Telmatactis decora in its claws as a defense strategy. This tiny crab manages to handle anemones that look oversized compared to its small body, making it a fascinating sight in the wild.
I heard that the teddy bear crab wears sponges as hats. I can’t precisely tell if this is the same species, as there are some other same-looking species that are referred to as teddy bear crabs, like the Polydectus cupulifer. If you know something about this, then let me know in the comments.
Pilumnus vespertilio was first described in 1793 by Fabricius, originally named Cancer vespertilio. This name has since changed, but its quirky behavior and special relationship with anemones remain a captivating part of its story. The anemones not only act as a shield but also add to the crab’s charming and resourceful nature, making it standout in marine environments.
Appearance
When I first spotted a teddy bear crab (Pilumnus vespertilio), its appearance immediately stood out. This unique crab, covered in short, fine hairs called setae, gets its nickname from its fuzzy, teddy bear-like look. Its body and legs are fully cloaked in fur, which isn’t just for show—this dense covering helps trap sand and sediment, making the crab blend seamlessly into the sandy seafloor. This camouflage is vital for its survival, letting it hide from predators with ease. The dark brown setae vary in length and create an almost fluffy appearance, which makes it quite memorable.
Teddy bear crabs don’t grow very large, typically reaching about 3-5 cm. I’ve noticed that their carapace width can get up to 3/4 inch, and more precisely, it’s about 1.4 times wider than it is long, measuring between 18-26 mm in length and 25-31 mm in width. What makes them even more intriguing are their asymmetrical chelipeds, adding to their distinct shape. Their legs are somewhat flattened, known as depressed, which helps them move easily across their rocky or sandy habitat.
I think one of the coolest things about the teddy bear crab is how nature equipped it with dense, hair-like setae for perfect camouflage. This adaptation gives them an effortless way to blend into their surroundings. If you’re ever lucky enough to spot one, take a closer look at how well it hides—it’s a marvel of nature that showcases how well creatures can adapt to their environment.
Are teddy bear crabs reef safe?
If you’re thinking of adding a teddy bear crab (Pilumnus vespertilio) to your reef tank, you should know that they aren’t reef-safe. These crabs have a natural instinct to feed on a variety of tank inhabitants, which includes soft corals, sponges, and even zoanthids. Their diet isn’t limited to invertebrates; if given a chance, they will go for small fish too.
I’ve learned that teddy bear crabs don’t shy away from an easy meal. If they can catch a small fish, they will eat it without hesitation. This can make them a risky addition to a tank with smaller, peaceful fish or delicate coral species. Even though their fluffy appearance is cute, their behavior in a tank can be anything but gentle.When keeping any crab, especially one as opportunistic as the teddy bear crab, consider its impact on the overall tank environment. While they can be fascinating to observe with their unique, furry look, they are best suited for tanks that don’t include vulnerable corals or tiny fish. Always research the tankmates you choose to ensure they coexist peacefully.
If they came with your corals, which is probably the case, consider keeping them in a sump or an extra mini tank.
Care and tank setup
When setting up a tank for a Teddy Bear Crab (Pilumnus vespertilio), I recommend starting with at least a 10-gallon tank. These crabs love to dig, so using a sand substrate works well. Adding live rock will give them hiding spots and help mimic their natural habitat. While they can be kept in a display tank, some aquarists choose to place them in a sump if they spot them causing trouble, as these crabs may nip at corals or small fish.
Maintaining proper water conditions is crucial. Aim for temperatures between 70-80°F (21-26°C), with a pH level of 8.0-8.2. Keep the salinity in the range of 30-41 ppt for the best results. These water parameters closely resemble their natural environment, helping them stay healthy and active. Following these care tips will ensure your Teddy Bear Crab thrives in captivity.
What do teddy bear crabs eat?
Teddy bear crabs (Pilumnus vespertilio) are known for their varied and opportunistic diet. In the wild, they feed on seaweed, different types of algae, small marine animals, and a range of invertebrates. I’ve noticed they don’t just stop there—they sometimes eat toxic zoanthids, which can make them mildly poisonous. In their natural habitats like those in Okinawa, Japan, they actively feed during peak summer months, scrubbing coralline algae surfaces for food. After August, their strategy changes as they start carrying algae-covered objects and animal material to their burrows for later. This behavior helps them survive when food becomes less accessible.
These crabs consume over 22 types of algae, including Gelidium pussilum, and occasionally eat animals like brittle stars. Females seem to have fuller stomachs, especially during reproduction, and rely more on stored food from their hepatopancreas than males. This detail highlights how females adapt to their needs during different seasons.
In an aquarium, teddy bear crabs show similar feeding habits and will eat a diet rich in algae, shrimp, fish, and other leftover meaty foods. I always say, be mindful of their carnivorous tendencies since they can easily prey on tankmates if the opportunity arises. So, if you decide to keep one, make sure there’s enough food to satisfy their appetite and prevent them from turning into unexpected predators.
Breeding
Teddy bear crabs (Pilumnus vespertilio) have a fascinating breeding cycle that I’ve found quite intriguing. They seem to breed most actively in March and December, especially in regions like East Africa. This timing isn’t random; it aligns with environmental factors that boost their reproduction. During these months, females carry yolky eggs beneath their abdomens, which hatch into larvae after fertilization. The larvae pass through three zoeal stages and a megalopal stage before finally settling on the seafloor.
In East Africa, these crabs keep a continuous breeding cycle, but peak egg production occurs in March and December. From April to July, egg production slows down. Males and females mature their reproductive organs from winter to summer, with females releasing eggs mostly in the summer. Females molt twice a year (January–March and October–December), while males primarily molt in October–December. Warmer temperatures and higher rainfall can trigger more egg-carrying females, and larger females often carry anywhere from 300 to 8,000 eggs.
An interesting detail I want to share is how these crabs time their reproduction with the lunar cycle. Mating usually peaks after the full moon, aligning egg release with spring tides. This timing helps larvae spread into open water, boosting their chances for survival. I’ve found that higher water temperatures and increased rainfall can make breeding more frequent, ensuring a thriving crab population.
