“Lawn shrimp” is the common name for small, terrestrial crustaceans that become noticeable in yards after heavy rain or irrigation. Despite the name, these creatures are not true shrimp but are a type of land-dwelling amphipod. They thrive in damp, organic-rich environments and are typically harmless members of the garden ecosystem.
True Identity and Classification
The creature commonly called a lawn shrimp belongs to the order Amphipoda, a group of crustaceans that includes species like sand fleas and scuds. Unlike true shrimp, these terrestrial amphipods lack a hard outer shell, or carapace. They have a body that is compressed laterally, meaning they are flattened from side to side, which is a distinctive feature of the Amphipoda order.
An adult lawn shrimp typically measures between one-quarter to three-quarters of an inch (0.6 to 2.0 cm) in length. Their coloration varies, appearing translucent, pale pink, or brownish-black when alive. When they die, however, they often turn a noticeable dark brown, pink, or red color, which is why dead clusters are frequently observed on sidewalks and patios. They possess two pairs of antennae and multiple pairs of legs, with some of the rear legs adapted for jumping, a characteristic that earns them the alternate common name “landhopper.”
Habitat Requirements and Behavior
Terrestrial amphipods are entirely dependent on high moisture levels because they lack the waxy layer on their exoskeleton that insects use to retain water. This physiological limitation means they are highly sensitive to changes in humidity. They are found in the top half-inch of soil or mulch, thriving in damp, shaded areas with plentiful organic material like leaf litter and decomposing wood.
Their role in the ecosystem is that of a detritivore, meaning they feed primarily on decaying organic matter. Lawn shrimp actively consume dead leaves, fungi, algae, and other plant debris, which helps break down material and recycle nutrients back into the soil. They are beneficial contributors to soil health and the natural decomposition process. They are mostly active at night, foraging for food and burrowing through the moist ground.
Impact on Yards and Structures
Lawn shrimp do not bite, sting, or pose any threat to humans or pets. They are, however, known to be an occasional nuisance, particularly when weather or irrigation conditions force them out of their preferred habitat.
When their environment becomes oversaturated from heavy rain or excessive watering, they are driven out of the waterlogged soil to seek drier ground. Conversely, if their habitat dries out too much, they may also migrate in search of moisture. This migration can lead them onto driveways, patios, and sometimes indoors through small gaps or under doors. Once inside a structure, the dry indoor air rapidly causes them to desiccate and die, often resulting in noticeable clusters of dead, reddish-pink crustaceans near entry points.
Managing Nuisance Populations
Since lawn shrimp populations are directly tied to moisture, the most effective management strategy involves modifying the environment to make it less hospitable. Reducing excessive irrigation is a primary step, as overwatering creates the ideal damp conditions these amphipods need to reproduce and thrive.
Environmental Modifications
- Ensure that lawns and garden beds have proper drainage to prevent the waterlogged soil that triggers their mass exodus.
- Clear away heavy accumulations of organic debris near the home’s foundation, including excessive leaf litter, old wood, and thick layers of mulch, as these materials retain moisture and provide a food source.
- If mulch is used, keeping the layer to a depth of two to three inches or less is recommended to allow the area to dry more efficiently.
Exclusion and Chemical Use
To prevent indoor entry, sealing cracks in the foundation and installing door sweeps can exclude the migrating creatures. Chemical treatments are rarely necessary or recommended, as they do not address the underlying moisture issue and are often ineffective against these crustaceans.