Fairy Shrimp

March 08, 2021

Fairy Shrimp from the Homer Lake Wetland

Although these creatures look like concept drawings for characters in a yet-to-come Star Wars movie, they are actually small fresh-water crustaceans (think crabs, lobsters and shrimp) that inhabit ephemeral (temporary) ponds. You may rightly wonder how a fully aquatic animal such as the fairy shrimp survives from year to year in ponds that dry up completely most years. It is, after all, the fact that they dry up completely on a regular basis that makes them unsuitable habitat for fish and it is the absence of fish that makes such ponds particularly attractive for many other types of animals such as spring peepers, chorus frogs and the fairy shrimp.

So how do fairy shrimp survive when there is no water? Female fairy shrimp lay two types of eggs. One type has a thin shell and will hatch the same season that it is laid. The other type has a much tougher outer covering and will not hatch until the pond has dried out and then has water again. This guarantees that there will be fairy shrimp swimming around in future years. In fact, water often returns to these ponds by the middle of winter, and it is often possible to see fairy shrimp swimming around under the ice. These tougher eggs are even able to pass through the digestive system of water fowl unharmed and so can be transported from one ephemeral pond to another.

Fairy shrimp have two pairs of antennae and ten pairs of leg-like appendages that they use for swimming-- they swim on their backs, as you see in the photos-- and filtering food out of the water. They have an additional pair of appendages at the tail end. When fully grown, the body of the fairy shrimp consists of 20 segments. Segments are added as they grow. If you click on any of these pictures to view them larger, you may be able to count the segments and the pairs of legs. The large fairy shrimp in the photo above is probably about 1" long (I forgot to measure before releasing them back into the pond).