Fairy Shrimp

Although they live in fresh or saltwater, they do not live in oceans or seas. They are well-adapted to living in arid areas where water is present for only part of the year. Often appear in vernal pools. Vernal pools are temporary pools of water usually located in Western United States such as California and also in New England.

During mating, the male swims under the female and grasps her with his antennae. He holds on for either several minutes or several days and then they separate. Inside the female's body the eggs are wrapped in yolk and a strong shell which has spikes or bumps on them. The eggs are put into the water and then sink to the bottom on the water, where they start developing. Females can produce two types of eggs, thin shelled "summer" eggs and thick shelled "winter" eggs. The type of egg produced is determined by the number of males. Summer eggs will be produced if there is a shortage of males in the population. Summer eggs hatch rapidly. The young from these eggs will populate the pool during the same season they are laid. The winter eggs remain in the mud at the base of the pool and dry out with the pool. The eggs will hatch in the spring when the pools refill.

Fairy Shrimp are about 1 to 1 ½ inch in length and spend their entire lives in vernal pools. Adult fairy shrimp have compound eyes, two sets of antennae, and 11 pairs of swimming legs. The body is divided into three parts: head, thorax, and abdomen. The two sets of antennae are called antennules, which are usually long. The second one (not named) is usually more muscular, especially for the males. Usually reddish-orange color but also can be gray or a translucent white color, or blue/green. The coloration of the fairy shrimp depends on what they eat or what’s in the water. Fairy shrimp swim on their backs using their multiple legs.

“The leg movements serve the purpose of collecting algae, bacteria, protozoa, rotifers and floating detritus from the water. Food is then filtered from the water and scraped by sets of appendages to be eaten using a mandible mouth. Fairy shrimp have been observed gnawing on larger matter such as dead tadpoles, mollusks and amphibian eggs. The leg movements of the fairy shrimp also serve the purpose of taking the oxygen the animal needs from the water. The ephemeral nature of the fairy shrimp reduces the limiting factors on their population. Fairy shrimp have few natural predators. They are unlikely to be heavily preyed upon by other vernal pool inhabitants because they utilize the pool before the majority of carnivorous insects have colonized the pool. Also, the wood frogs and mole salamanders breeding in the pools have not regained their regular appetite after winter hibernation and, thus, are not major predators.”