The sirens are generally regarded as the most primitive living salamanders. The ecology and natural history of sirens is poorly known. All sirens share a conspicuous basic characteristic: the absence of rear limbs. Another notable characteristic is the presence of external gills throughout life. Sirens are completely aquatic, rarely emerging from water unless absolutely necessary. The absence of hindlimbs and the relatively weak forelimbs make overland travel virtually impossible. But if, for instance, a body of water dries up, sirens are forced to deal with a terrestrial existence. Their solution? Wait for a better day. Sirens can secrete a cocoon, of sorts, in which they can aestivate, for more than a year, until the pond refills with water.
The sirens are common in ditches, lakes, ponds, Carolina bays, and streams in the Coastal Plain of South Carolina and Georgia. Reproduction usually occurs in the spring, and it is estimated that maturity is achieved in two to three years. Sirens are fairly nondescript, having a general drab appearance, olive to black in color with or without other markings. They have conspicuous external gills and four toes on each of the forelimbs. The designation "lesser" comes from the fact that most Siren intermedia are less than 2 feet long (total length), in contrast to the "greater" sirens, which are known to exceed 3 feet in length. For discriminating between the two species, authorities suggest counting costal grooves (external grooves along the sides of the animal in between forelimbs and the vent, which correspond roughly to the number of ribs. The greater siren usually has more than 36, whereas the lesser siren has less than 35 grooves. Sirens, like amphiumas, are effective predators of most aquatic animals.