The alkali fly, Ephydra hians, is a small insect, typically 4 to 7 millimeters long, known for its remarkable ability to thrive in environments inhospitable to most other life forms. Its unique life cycle and behaviors highlight how life can persist and flourish in unusual habitats.
Mono Lake’s Extreme Environment
The primary habitat for the alkali fly is Mono Lake, located in California’s Eastern Sierra Nevada. This terminal lake lacks an outlet, meaning water leaves only through evaporation. This process concentrates salts and minerals, making the lake hypersaline and highly alkaline. The lake’s pH can reach approximately 9.8, making it around 80 times more alkaline than the ocean, and its salinity can be two to three times saltier than seawater, depending on water levels.
The water of Mono Lake contains a high concentration of chlorides, carbonates, and sulfates, creating a “triple water” chemistry. This unique chemical composition makes the water feel slippery and even soapy. Fish cannot survive in these conditions, limiting the aquatic life to a select few species, including bacteria, algae, brine shrimp, and the alkali fly.
Survival in Extreme Conditions
The alkali fly possesses physiological and behavioral adaptations that enable its survival in Mono Lake’s harsh waters. Adult flies can dive underwater to feed and lay eggs, a feat that would drown most other insects. Their bodies are covered in a dense mat of water-repellent hairs (setae) and a waxy layer of hydrocarbons. This creates a “superhydrophobic” surface, allowing a stable air bubble to form around the fly when it enters the water.
This air bubble acts as a physical gill, protecting the fly from the caustic water and providing a supply of oxygen, enabling it to remain submerged for up to 15 minutes at depths of 4 to 8 meters. The high concentration of sodium carbonate in Mono Lake water makes it “wetter” than pure water, posing a challenge to the air bubble’s integrity; however, the alkali fly’s specialized cuticle effectively counters this. If a fly does get wet, a thin film of minerals can dry on its cuticle, increasing its vulnerability to future wetting.
Understanding Their Life Cycle and Behaviors
The alkali fly’s life cycle includes four distinct stages: egg, larva, pupa, and adult. Female flies will crawl underwater to lay her football-shaped eggs, typically 0.6-1.0 mm long, individually on benthic algal mats or other submerged substrates near the shore. The eggs, heavier than Mono Lake water, hatch into tiny legless larvae within 1 to 3 days, depending on salinity and temperature. Larvae undergo three developmental stages, or instars, molting their cuticle between each stage.
Larvae and pupae live entirely underwater, often found in shallow areas, particularly on tufa formations which provide excellent attachment sites. They feed on abundant algal mats and microbial detritus. The larvae have a unique physiological adaptation, a lime gland, which functions like a kidney to remove excess carbonate ions from their blood, combining them with calcium to form limestone stored within their bodies. Upon reaching the pupal stage, the puparium fills with air, allowing the emerging adult fly to float to the surface encased in a bubble. Adult flies, which live for 10 to 14 days, spend their time along the shoreline, feeding on algae and reproducing, though overwintering adults can survive for several months.
Role in the Ecosystem
The alkali fly plays a significant role in the Mono Lake ecosystem, forming a central link in its food web. As primary consumers, larvae and adult flies feed extensively on the abundant algae and bacteria in the lake. This consumption helps to manage algal growth and convert it into a readily available food source for other organisms.
The sheer numbers of alkali flies, often blanketing the shoreline in late summer, provide a rich source of fat and protein for millions of migratory and nesting birds. Species such as Wilson’s and Red-necked Phalaropes, California Gulls, Brewer’s Blackbirds, and Eared Grebes rely heavily on alkali flies and their aquatic stages. Some birds, like Wilson’s Phalaropes, employ unique feeding techniques, such as spinning in shallow water to create a vortex that brings larvae and pupae to the surface. Historically, the local Kutzadika’a Tribe, whose name means “fly eater,” also harvested alkali fly pupae as a valuable food source, drying them for use in stews or trade. The productivity of alkali flies is directly linked to the lake’s environmental conditions, making them an indicator of Mono Lake’s overall health.