Brown recluse spiders are often a source of public concern, due to misconceptions about their size and appearance. These reclusive spiders are among few North American species with venom that can cause medical issues. Accurate identification, based on their dimensions and distinguishing features, is important to alleviate unnecessary worry and avoid misidentification.
Understanding Brown Recluse Size and Key Features
Brown recluse spiders are not large. Their body length ranges from 6 to 20 millimeters (0.24 to 0.79 inches). With legs extended, adult brown recluses span about the size of a U.S. quarter. Females can have a leg span over 1 inch, while males are about half the size of females in body length but often have proportionally longer legs.
A defining feature of the brown recluse is a darker, violin-shaped marking on its cephalothorax, the fused head and chest region. The “neck” of this violin shape points towards the spider’s abdomen. While this “fiddleback” marking is characteristic, its intensity can vary and may be less distinct in younger spiders. The spider’s color is light to medium brown, ranging from whitish to dark brown or grayish. Their legs are uniformly colored, lacking stripes, bands, or spines, and their abdomen is also uniformly colored without patterns, though its shade can vary depending on what the spider has consumed.
A definitive identifier for the brown recluse is its unique eye arrangement. Unlike most spiders that possess eight eyes, brown recluses have six eyes. These eyes are arranged in three pairs (dyads) forming a semicircle: one median pair and two lateral pairs. This specific eye pattern is uncommon among spiders, making it a reliable way to differentiate them from other species.
Common Misidentifications and Look-Alikes
Many spiders are mistaken for brown recluses due to similar coloration or general shape. Wolf spiders, for instance, are confused with brown recluses because of their brown or grayish hues. However, wolf spiders are larger and hairier, with more robust bodies. They also possess eight eyes arranged in two distinct rows, often with two larger eyes in the front, differing from the brown recluse’s six-eye pattern. Wolf spiders have distinctive dark stripes or patterns on their backs and bristly legs, unlike the uniformly colored legs of a brown recluse.
Hobo spiders are another common look-alike, sharing a brownish coloration. They have a mottled appearance with darker and lighter spots or faint chevron patterns on their abdomen, which brown recluses lack. A key difference lies in their eyes: hobo spiders have eight eyes arranged in two rows, contrasting with the brown recluse’s six eyes. Hobo spiders also build funnel-shaped webs, whereas brown recluses spin irregular, messy webs used more for retreat than for trapping prey.
Common house spiders, often yellowish-brown, can also be mistaken for brown recluses. These spiders usually have a rounder abdomen and may display various patterns or markings, including white or dark brown spots and stripes. Unlike the brown recluse, common house spiders have eight eyes and often construct tangled, messy webs in corners, which they use to catch prey.
The southern house spider is another brown spider sometimes mistaken for a brown recluse due to similar color and size, but it has eight eyes grouped closely together and lacks the violin marking. Other spiders, such as cellar spiders and woodlouse spiders, also share some superficial resemblances but can be differentiated by their eye arrangement, body shape, or the presence of spines on their legs.