Grassland Crayfish

Arthropods are one of the largest groups of animals within the animal kingdom, comprised of insects, spiders, and their kin, as well as all manner of sea life like shrimp, crabs and even lobsters. Recently, after one of the recent storms we have been experiencing here in Northwest Missouri, we noticed our granddaughters pool had blown away into the ditch along the highway. After retrieving it, a crayfish was discovered using it as a convenient hiding spot. After taking a few pictures, it was released into our garden pond to live another day. There are over 500 species of crayfish in the world and more than half live in North America. 

This particular crayfish is the grassland crayfish, or prairie crayfish as it is also known as. Crayfish in general go by many different names, including crawdads, mudbugs, and lawn lobsters. Grassland crayfish are somewhat common in Missouri and like their name suggests are found in open grasslands and prairies, however with the reduction of those available habitats, they often use temporary wetlands, or wet ditches (such as the one we found). Historically much of Missouri was made up of tall grass prairies. With the increased need of land in the agricultural industry, and the overall expansion of cities with exponential growth and development Missouri has lost more than 95% of its native prairies and grasslands. The remaining remnant prairies are predominantly owned by the Missouri Department of Conservation, The Nature Conservancy, private landowners, as well as a few other conservation minded organizations. These remaining small prairies should be protected for many reasons, but chief among them to guarantee the survival of the plant and animal species that rely on them.

The grassland crayfish is an average sized crayfish reaching lengths up to three inches, and may be red, or reddish-brown with little to no spots or blotches. They resemble another crayfish that lives in our state called the devil crayfish, but unlike the grassland species, the devil crayfish will never be uniformly red. While these crayfish are considered somewhat common in Missouri, they are rarely encountered by humans because of their secretive nature and nocturnal habits. These crayfish dig burrows using their claws to excavate and their tail to carry the dirt to the surface and pile it around the opening in a chimney sort of fashion. During the heat of summer, they remain underground in these burrows, which may be more than six feet deep. During the evening hours they will come to the surface and seek food or mates. Decomposers by nature, these omnivores eat both animal and plant matter and are able to break down plants highly resistant to decay. 

Due to their impact on the environment, they are often thought of as ecosystem engineers. Crayfish come in three classifications. The primary burrowers, secondary burrowers, and tertiary burrowers. The primary excavators may burrow up to fifteen feet underground far away from water, secondary excavators dig burrows closer to water and may have tunnels that reach bodies of water, the tertiary species typically do not dig burrows, and instead reside within bodies of water hidden under debris or rocks. The burrows they dig allow nutrients to reach the roots of plants and create passages for rainwater to reach deeper into the earth. Many animals like the Northern crayfish frog, snakes and small mammals use the burrows created by these excavating crayfish as shelters. In the case of the crayfish frog, a species of conservation concern in our state, they rely heavily on the burrows created by the grassland crayfish. Like the crayfish, the crayfish frog inhabits prairies, and with the reduction of prairies and available burrows the crayfish frog struggles to survive. When we destroy one component of the environment, it nearly always has a trickle-down effect on everything in the food chain of that environment. Destroy the prairie, the crayfish has no place to burrow, no burrows will impact plants, and removes the sheltering areas the crayfish frog relies on, with the loss of the frog Missouri loses one of its most unique amphibians. It is vitally important that we conserve the remaining prairies and grasslands we have and continue to restore land back to its historical prairie state when possible

Crayfish are also considered important indicator species of water quality, because of their intolerance of polluted water sources. With the absence of crayfish in an area where they would typically be, scientists can begin studying the possible reasons for their absence. This allows for quicker intervention in potential environmental catastrophes. The opposite can be said as well, the presence of crayfish should indicate clean, healthy water.

Crayfish play an important role in the medical field. There is evidence that crayfish experience similar anxiety as humans. Scientific experiments have been conducted that showed crayfish exposed to stressful situations will have an increased anxious response and not behave in normal ways to existing environmental conditions. These crayfish were given an electrical shock and then placed in a cross shaped tank. Two arms of the cross were lit up brightly, and two arms were dark. Those crayfish that were shocked always went into the dark arms and avoided the light. When injected with a common antianxiety drug, used by humans today, the crayfish were seemingly calmer and bolder and would explore all arms of the tank. This knowledge has huge implications in the understanding and treatment of anxiety disorders in humans. Just one more reason to appreciate these little crustaceans.

Crayfish reach reproductive age between five and six years. Males will molt into their breeding form with larger claws, a longer body, sharper spines, and a tougher exoskeleton. Being larger and tougher helps them battle other males during mating season. Once mating season is over, however, they molt again, after which they resemble their pre-breeding form once more. 

Breeding rituals of crayfish tend to be an aggressive affair with much fighting between males. Dominate crayfish that win fights against other males will behave aggressively towards other crayfish and even towards their own reflections. Subordinate crayfish who lose fights avoid their reflections and walk backwards to keep an eye on other crayfish in a timid fashion. Those who fall into either category typically stay in that role. In other words, Winners remain winners and losers remain losers. It was once believed that crayfish in the dominant role released some sort of pheromone the female could smell and thus were able to better choose an appropriate mate. Now there is some indication based on laboratory studies that this isn’t the case. Instead, they participate in a primitive sort of eavesdropping. They are hidden on the sidelines, watching the fight and when the winner emerges, she will allow mating with that individual. In other words, she isn’t taking his word for it, she needs to see it for herself. After mating the female will carry the eggs attached to her swimming appendages. They will remain with her two to twenty weeks before hatching. As newly hatched crayfish they remain connected to their mother through a stalk-like appendage. After molting the stalk no longer keeps them attached to the mother, however she will still carry them with her for two weeks or more. These tiny crayfish babies are able to wander on their own, but often return to the safety of their mother for a period of time.

These often-overlooked arthropods are important members of the environments they occur in. They serve various roles from soil excavators, decomposers, indicator species, landlords to frogs and other wildlife, food for a wide variety of animals, including humans and medical specimens for scientific research that benefit human health. Sometimes the lowliest of creatures fill the most important roles.