Greater Siren

Greater siren（圖片來源：Wes Anderson，採用 CC BY 4.0 授權）

The greater siren (Siren lacertina) is one of the largest amphibians in North America and belongs to the family Sirenidae. Its elongated, eel-like body gives rise to its common name. It is widely distributed across the southeastern coastal plains of the United States, ranging from Washington, D.C. southward to Florida and westward to Alabama. Scattered populations have also been reported in Texas and northeastern Mexico, although the identity of the latter still requires genetic confirmation.

The greater siren is a neotenic amphibian, meaning it retains its external gills even in adulthood and does not undergo metamorphosis to a terrestrial form like many other salamanders. It lacks hind limbs and a pelvic girdle, possessing only very small forelimbs that appear almost hidden behind the gills. Adults typically reach 50 to 97 cm in length, with maximum records approaching 1 meter. However, it is not the longest salamander; species such as Amphiuma means, Andrias japonicus, and Andrias davidianus can reach greater lengths. Its coloration is usually olive green or gray with yellow-green spots along the sides. Juveniles display distinct pale lateral stripes that gradually fade with age.

In the wild, greater sirens inhabit swamps, lakes, rice fields, canals, and slow-moving sections of rivers, preferring environments with thick mud substrates and abundant aquatic vegetation. They are nocturnal, remaining hidden during the day within submerged logs, vegetation, or mud, and becoming active hunters at night. Their diet is primarily carnivorous, including insects, crustaceans, mollusks, and small fish. They show a strong preference for snails and freshwater bivalves, although algae and plant fragments have occasionally been found in their digestive tracts, suggesting incidental or occasional plant consumption.

Their predators include American alligators and mud snakes, but due to their large size and aggressive behavior, they function as important mesopredators within wetland ecosystems. During drought or when water bodies dry up, they can enter estivation, burrowing into mud and forming a thin cocoon made from shed skin. In this state, they may remain dormant for months or even years, with experimental records showing survival up to five years, demonstrating remarkable environmental resilience.

Their lifespan in the wild remains unclear, but captive individuals have been recorded living up to 25 years. Artificial breeding is extremely rare and has a very low success rate, so most individuals available in the pet trade are wild-caught from North America. According to the International Union for Conservation of Nature (IUCN), the species is currently classified as Least Concern, although local declines due to habitat loss indicate that populations still require monitoring.

Housing Requirements in Captivity

Keeping a greater siren as a pet requires careful consideration, as it is a large, active, and long-lived aquatic salamander with substantial environmental needs.

• Tank size: Adult greater sirens require an aquarium of at least approximately 380 liters to ensure adequate space for movement. Individuals can approach 1 meter in length, and insufficient space may lead to stress and health problems.

• Water quality and filtration: Clean and stable water is essential. A strong filtration system such as a canister filter is recommended, along with regular water changes. Avoid substrates that alter pH. While the species tolerates a wide temperature range, the optimal water temperature is 21 to 24°C.

• Substrate and environmental setup: Although they prefer muddy bottoms in the wild, fine sand or coarse gravel is more suitable in captivity to prevent water turbidity. Provide abundant hiding places such as PVC pipes, ceramic pots, driftwood, and artificial plants, allowing complete concealment. As nocturnal and highly alert animals, secure hiding spaces help reduce stress.

• Safety measures: The aquarium must have a secure lid, as greater sirens are prone to escape, especially during nighttime activity. Some keepers recommend placing cloth or towels beneath the lid to prevent injury from repeated nose rubbing in newly introduced individuals.

• Lighting: UVB lighting is not required. Low-light conditions better match their nocturnal behavior. If observation is desired, night-viewing lights can be used.

Greater siren in an aquarium（圖片來源：Qualiesin，採用 CC BY-SA 4.0 授權）

Feeding Conditions

The greater siren is an opportunistic carnivore with a broad diet. In captivity, feeding should follow these guidelines:

Primary food sources

• Fish: Small freshwater fish such as guppies, crucian carp, or minnows can serve as staple foods.

• Invertebrates: Crayfish (with claws removed to prevent injury), shrimp, earthworms, and crickets are excellent food items.

• Mollusks: Snails and freshwater bivalves are particularly favored.

• Other: Frozen shrimp and commercial amphibian or reptile diets may also be accepted by some individuals.

Occasional foods

• Small frozen mice can be offered occasionally for dietary variety, but reliance on mammalian meat should be avoided to prevent obesity and metabolic issues.

Feeding is best conducted at night to align with their natural activity patterns. Using feeding tongs is recommended to avoid accidental bites. Food quantities should be controlled so that all food is consumed within a short period, preventing water contamination. Adult individuals can be fed 2 to 3 times per week, while juveniles require more frequent feeding.

Breeding Conditions

The reproductive behavior of the greater siren remains poorly understood in the wild, and successful captive breeding is extremely rare. Therefore, reliable methods for artificial breeding cannot be provided.

The breeding season occurs mainly from February to March. Females lay approximately 500 eggs, which are scattered on the substrate or among aquatic vegetation. Males guard the eggs, fanning them with their tails to maintain water circulation and prevent fungal infection, while aggressively driving away intruders, including females. After about two months, the eggs hatch into larvae, and the male departs. Juveniles initially inhabit shallow waters or areas near plant roots before moving into deeper water as they grow.

Preventing Invasive Spread

The greater siren is native to North America but may appear in the global pet trade. Owners must take full responsibility and never release them into non-native environments. The release of any non-native species can lead to ecological disruption. Due to their large size, long lifespan, and broad diet, greater sirens may exert strong predatory pressure on local fish, crustaceans, and mollusks, potentially altering wetland ecosystem structure. Their ability to survive prolonged drought through estivation further complicates eradication efforts, as they can remain buried in mud for years even after water sources disappear. Therefore, under no circumstances should they be released. If an owner can no longer care for the animal, it should be rehomed to an experienced keeper or transferred to a legal animal care facility.

Author: Shui-Ye You