The shallow ground water habitats where Hay’s Spring amphipod is found are known as hypotelminorheic, meaning shallow groundwater habitats that are not exposed to light and are vertically isolated from the water table below. These habitats are perched aquifers underlain by a clay layer typically 2 to 20 inches (5 to 50 centimeters) below the surface. They are also high in organic matter. The area where water from these habitats exits to the surface is known as a seepage spring.

Forest cover is an important aspect of the Hay’s spring amphipod habitat. Trees provide food for the species through decaying leaves and organic matter. Tree cover also helps to maintain water quality by filtering out pollutants and keeping water temperatures cool. Spring sites with Stygobromus species have unique water chemistry; compared to other shallow water spring habitats they have higher conductivity and dissolved oxygen and lower pH and temperature. Tree cover also influences the amount of water available for the shallow ground water habitats. Higher amounts of tree cover help to slow down storm water and allow it to infiltrate.

Although traps containing shrimp have been successful at capturing Hay’s Spring amphipod, the food requirements of the species are currently unknown. Captive specimens of other amphipods in the genus Stygobromus have been observed feeding on protozoans, flatworms, organic debris and plant material.

Because the species spends so much of its lifecycle underground, behavior characteristics of the Hay’s Spring amphipod are hard to observe. Other amphipods in the genus Stygobromus use a crawler mobility. It is assumed that the species gets flushed into seepage springs at the surface during high water events, and that it is able to burrow into the clay layer during times where there is low flow in its ground water habitat.

The Hay’s Spring amphipod is shaped like a tiny shrimp. Males are slightly larger than females.

Measurements
Male length: 0.39 inches (9.8 mm)
Female length: 0.28 inches (7.0 mm)

Hay’s Spring amphipods are modified for life underground and are colorless with no eyes.

Not a great deal is known about the Hay’s Spring amphipod life cycle, but it is presumed that they hatch from eggs and have a brief juvenile stage before becoming adults. In other Stygobromus species, juveniles resemble adults and go through a number of successive molts before becoming mature.

The lifespan of the Hay’s spring amphipod is unknown, but based on other subterranean amphipod species it is assumed to be 4 to 6 years.

Females of the species contain a brood pouch, which suggests that reproduction occurs via eggs and that females provide some degree of care to the eggs. It is unknown if reproduction is entirely sexual or asexual as well. Males and females have been found during collections, but parthenogenesis, a form of asexual reproduction in which embryos develop without fertilization, is reported in some Stygobromus species. The age and size when individuals become sexually mature is unknown.