Woodlice are common terrestrial crustaceans frequently encountered in damp, dark environments. These small creatures, often found beneath rocks, logs, or leaf litter, are not insects but are more closely related to marine animals such as crabs and shrimp.
Overall Appearance
Woodlice typically exhibit a flattened, oval body shape, usually measuring between 0.7 to 18 millimeters in length, with an average size of about 10 millimeters. Some larger species, like the common sea slater, can grow up to 30 millimeters. Their coloration commonly ranges from grayish-brown to dark gray or black, though some species may display lighter markings, or even yellow or pink hues.
The body of a woodlouse is covered by a segmented, shell-like exoskeleton, often described as having an armored or bumpy texture. This protective outer layer helps them retain moisture, essential for their survival in terrestrial environments. The exoskeleton is shed in two stages as the woodlouse grows, with the back half molting first, followed by the front.
Detailed Identifying Characteristics
A woodlouse’s body is distinctly segmented, divided into two main regions: the thorax, also known as the pereon, and the abdomen, or pleon. The pereon consists of seven segments, each bearing a pair of legs. This arrangement results in a total of seven pairs of legs, supporting their movement across various surfaces.
Woodlice possess two pairs of antennae. One pair is longer and more prominent, used for detecting environmental vibrations and navigating their surroundings. The second pair, shorter, functions as chemoreceptors to sense chemicals in their environment. At the rear, woodlice have tail-like appendages called uropods, which can aid in navigation and, in some species, secrete chemicals for defense.
Telling Them Apart
Distinguishing between different types of woodlice is based on physical traits and behaviors. The term “woodlouse” refers to a broad group, but two common forms are often confused: the sow bug and the pill bug. These common names differentiate species based on their defensive mechanisms.
Pill bugs, also known as roly-polies, can roll completely into a tight, spherical ball when disturbed. This defensive posture protects their softer underside. They have a more rounded body and lack prominent tail-like appendages. In contrast, sow bugs cannot roll into a complete ball due to their flatter body and two noticeable, tail-like uropods. Both types prefer damp, dark habitats due to their susceptibility to moisture loss.