What Do Crayfish Eat?

Researchers recently discovered two new crayfish species: the Okanagan crayfish and the misfortunate crayfish (Pacifastacus malheurensis). Because both species were previously thought to be signal crayfish, the discovery comes as a surprise. These sneaky crustaceans required advanced genetic analysis to identify them as separate species. Unfortunately, these newly-discovered crayfish are already at risk, primarily due to competition with non-native crayfish for habitat and food. So, what kind of habitats do crayfish need, and what do they eat?

The Crayfish Habitat

Crayfish, also called crawdads or crawfish, are freshwater crustaceans that look like small lobsters. Crayfish prefer flowing aquatic habitats such as rivers and streams. However, they can also be found in habitats such as lakes, ponds, marshes, and swamps. There are over 700 crayfish species found all over the world. Researchers estimate that around 70% of all crayfish species live in U.S. waters.

Crayfish are burrowers, but they do not all burrow to the same extent. Primary burrowers dig elaborate burrows underground in wet fields, ditches, and meadows. They spend most of their time there, generally only leaving to mate or forage for food. Secondary burrowers dig less complex burrows that are usually connected to a permanent source of water. They are likely to be found in the water except during winter. Tertiary burrowers live in permanent bodies of water. They only leave the water to create a shelter in dire circumstances.

The Crayfish Diet

Crayfish are omnivorous scavengers, meaning they eat both plant and animal matter, whether living or dead. They are also opportunistic, so they eat whatever they can find. Adult crayfish tend to be more herbivorous. They favor a diet of aquatic plants, algae, leaves, and twigs. However, young crayfish are carnivorous. They prefer animal matter, including aquatic insects, snails, tadpoles, salamanders, and fish. Researchers have found that crayfish of any age are cannibalistic.

Because crayfish are opportunistic, their diets vary depending on what types of food are most readily available in their native habitat. For example, a crayfish living in a pond in Michigan might eat more pondweeds, while a crayfish inhabiting a Tennessee river would likely eat more southern naiad.

Allowing for some variation among species, the following list includes the different types of foods that crayfish eat:

• Decaying plant and animal matter
• Leaves and twigs
• Fish and fish eggs
• Plankton and algae
• Aquatic plants
• Insects and other invertebrates
• Insect larvae
• Amphibians
• Smaller crayfish

The Crayfish Digestive System

Like most crustaceans, the crayfish digestive system is not overly complex. After ingesting food through their mouths, the food moves through the esophagus to the crayfish’s two-part stomach. The cardiac stomach stores food and mechanically breaks it down. Crayfish and other crustaceans have teeth in their cardiac stomachs, called the gastric mill. These teeth grind and crush the food before it moves to the pyloric stomach for further digestion.

The pyloric stomach chemically breaks down the food, similar to the stomachs of vertebrates such as humans. Crayfish have digestive glands that produce acids to help with the breakdown process. Their intestines absorb nutrients from the food, then undigested food and waste is excreted from the anus.