Lesser sirens have elongated bodies possessing only two limbs, a pair of four-toed legs located behind the base of the head, and range in length from 7 to 27 inches (17 – 69 cm).

Adults have plainer coloration; the dorsal side is typically olive green to blue-gray or black, while the ventral is usually light grey.

Sirens are considered poor overland dispersers because they rarely leave the water, so their geographical distribution is largely determined by pond connectivity and biotic interactions.

[7] Lesser sirens are aquatic salamanders, but their ability to withstand factors like dehydration allows them to have good survival skills in their ephemeral habitats.

Sirens are able to osmoregulate and produce a mucoid cocoon during aestivation, which greatly reduces dehydration and electrolyte stress.

Their ability to aestivate and burrow in soft sediments and live in dense aquatic vegetation in shallow waters facilitates their dominance.

Like almost all species of amphibian, their numbers are believed to be declining due to general reductions in water quality caused by agricultural pesticide and fertilizer runoff.

The lesser siren is known to emit a series of clicks when it approaches others of its species, or a short screeching sound if handled.

Acoustic behavior serves a functional service in S. intermedia, especially since it is nocturnal and it burrows in sediments, swims and crawls through densely vegetated waters.

Nevertheless, acoustic behavior in lesser sirens is still infrequent, and becomes even less frequent with undisturbed habitat residency, perhaps because of their familiarity with the environment.

When S. intermedia butt or bite each other in their habitat, the bitten or injured individuals may swim away quickly, emitting yelps at frequencies of 880 Hz.

They also eat several insects and their larvae, crayfish, mollusks, amphibians, siren eggs, and algae, although the plant material may be an incidental result of their gape-and-suck feeding style.

[19] The lesser siren is nocturnal, spending its days hidden in the debris and mud at the bottom of slow-moving bodies of water.

The lesser siren's strategy to withstand the rigors of these dry seasons is something called "aestivation", or summer dormancy, which can last up to 35 weeks, depending on the severity of the drought.

During the sixteen-week period from July to October, aquatic lesser sirens increase the osmotic concentration of their body fluids, and slow down bodily functions.

As expected, large individuals store more fat and consume less oxygen per unit weight than small ones, and thus can survive much longer periods of aestivation.

Some individuals, especially the smaller sirens during aestivation, die or suffer from dehydration as they are unable to store sufficient fat and the greater metabolic demand reduces their chance of survival.

[21] As the drought season comes to an end, lesser sirens become active within a day, and slowly regain the lost weight over the next 8–11 weeks.

[4] During oviposition, the female turns on its back, positions the cloaca near the top of the nest cavity and halts for several seconds.

After the female completes oviposition and leaves the nest, the male stays in close proximity to the eggs and takes the responsibility of parental care.

Additionally, the male continuously cleans the nest from sand and other materials, to improve hygienic conditions and possibly to prevent infections from pathogens and fungi.