Pom Pom Crab – Lybia tessellata

Overview:
Pom Pom Crabs (usually Lybia spp.) are tiny marine crabs known for carrying small anemones in their claws. They do best in stable, mature reef aquariums with plenty of rockwork, crevices, and shaded overhangs for hiding. Aim for typical reef parameters: 24–26°C (75–79°F), salinity 1.024–1.026, pH 8.1–8.4, and very low ammonia/nitrite with modest nitrate. They are sensitive to rapid swings, so prioritize consistent top-off, gentle acclimation (drip acclimation is recommended), and steady alkalinity/calcium/magnesium if you keep stony corals. Moderate flow and reef-appropriate lighting work well; the crab will choose sheltered spots regardless of brightness. Secure the tank—small crabs can squeeze through gaps.

Compatibility:
These crabs are generally peaceful, secretive, and best kept with calm reef inhabitants. Good tankmates include small, non-aggressive fish (gobies, firefish, small wrasses with caution), snails, and many corals. Avoid predatory fish and invertebrates that see small crabs as food: hawkfish, larger wrasses, triggers, puffers, dottybacks, lionfish, and many larger crabs. Also avoid aggressive shrimp (especially large coral-banded shrimp) that may harass or outcompete them. They may steal food from corals or pick at very small polyps if underfed, so consistent feeding helps. Keeping multiple Pom Pom Crabs can work in larger systems with ample hiding spaces, but they may spar or compete for territory.

Health and Quarantine:
Most issues stem from poor acclimation, unstable salinity, or exposure to copper and other invertebrate-toxic medications. Never treat a display with copper if the crab is present. A short invertebrate observation period in a separate, stable tank can help screen for pests and confirm normal behavior and feeding, but avoid harsh dips. Watch for failed molts (lethargy, inability to shed, missing limbs) which are often linked to stress or parameter swings; stable conditions and adequate nutrition improve molting success. Provide iodine only via normal water changes unless you have a proven deficiency, as overdosing can be harmful. Signs of trouble include prolonged inactivity outside hiding spots, loss of grip, rapid decline after salinity shifts, or repeated harassment by tankmates—address water quality and compatibility first.

Omnivore

Plankton Leftover Fish Food Detritus
Pom Pom Crabs are peaceful, reclusive scavengers that spend most of their time hidden within rock crevices, emerging primarily at night to forage. They carry tiny anemones in their claws, waving them rhythmically to capture suspended food particles and detritus as they move through the tank. Their behavior is calm and unobtrusive, and they avoid conflict with other tank mates, making them well suited for peaceful reef systems. Though shy during the day, their nocturnal activity contributes to subtle but consistent cleanup, and their unique appearance provides a charming visual element for observant hobbyists.

FAQ

Frequently Asked Questions

About the Pom Pom Crab

  • My Pom Pom Crab only comes out when the lights are low. Is it unhealthy, or is this normal behavior?
    This is normal. Pom Pom Crabs are naturally cryptic and prefer dim conditions where they feel less exposed. In the wild, they stay deep inside rock crevices during the day and become more active at dusk. As long as it emerges for food and shows steady movement when it does appear, this is typical behavior for the species.
  • One of my Pom Pom Crabs dropped one of its anemones. Will it survive without it?
    Yes. Pom Pom Crabs occasionally lose or intentionally split their anemones. They can continue feeding and behaving normally even with one or none. Many individuals eventually regrow anemones by encouraging a piece to clone or by picking up available small anemones in the tank. Losing one is not a sign of illness or decline.
  • My Pom Pom Crab waves its anemones at fish when they swim close. Is this aggression?
    This is a defensive display, not true aggression. Pom Pom Crabs use their anemones to signal “stay back” to fish that get too close. The anemones deliver mild stings to predators in the wild, but in aquariums, this display rarely harms tank mates. It is simply a natural reflex triggered by movement near the crab’s hiding spot.
  • Can Pom Pom Crabs live in pairs or groups, or will they fight?
    They can live in pairs or small groups in larger reef tanks, but they will not interact frequently. Pom Pom Crabs are solitary and very shy, so most encounters happen accidentally while foraging. They do not typically fight unless confined to very small spaces. In tanks over 20 gallons with ample rockwork, multiple individuals coexist peacefully.
  • My Pom Pom Crab keeps dropping food while eating. Is it having trouble feeding?
    Not necessarily. Pom Pom Crabs use their anemones to catch suspended particles, and dropping food can be part of how they position it between their claws. They are delicate feeders and may release bits while sorting edible particles from detritus. Offering very fine foods like rotifers, phytoplankton, or micro pellets helps ensure they receive enough nutrition.