The brown recluse spider (Loxosceles reclusa) is a common source of concern in the midwestern and south-central United States. While these spiders produce silk, they do not use it to spin the large, intricate snares associated with orb-weaving species. Instead, the brown recluse uses its silk for a practical and less noticeable purpose. Understanding this function is more effective than searching for a traditional web.
The Use of Silk for Shelter
The brown recluse is a nocturnal hunter, actively stalking its prey rather than trapping it in a large web. Consequently, the spider does not spin the familiar, sticky web intended to catch flying insects. Instead, the silk is used to construct a messy, irregular, and loosely woven structure that serves as a protective retreat. This structure is often referred to as a “retreat sac” or “shelter web,” and it is typically hard to spot.
The retreat sac is frequently found in secluded, undisturbed locations, serving as the spider’s resting place during the day. Female brown recluses also use this silk to create small, off-white egg sacs, which are placed within the retreat to protect the developing spiderlings. The silk is constructed as a flat ribbon incorporating microloops, making the fiber tough and strong. This chaotic, off-white web signals the spider’s presence, but it is not used for hunting.
Preferred Habitats and Hiding Spots
Since the web is not an effective warning sign, knowing where the brown recluse seeks shelter is the primary factor for avoidance. These spiders prefer dark, dry, and secluded environments, mimicking the natural cover found under rocks and logs. They are common in undisturbed areas of human dwellings, such as attics, basements, and crawlspaces, where they retreat from light and activity.
Cluttered storage areas are attractive to the brown recluse, which often seeks refuge in boxes, especially cardboard. Cardboard is favored because its structure mimics the rotting tree bark the spiders inhabit outdoors. Contact with humans most frequently occurs when a person disturbs these secluded spots, such as when moving stored items or cleaning out a garage.
The spiders often hide in items that offer a dark, enclosed space, increasing the risk of accidental contact. This includes shoes, boots, and clothing that have been left on the floor or stored. They may also hide within bedding, towels, or under furniture that is rarely moved. Reducing clutter and shaking out clothes and shoes before use are simple, effective precautions against accidentally trapping one of these spiders.
Key Identification Markers
Relying on the presence or absence of a large web is misleading, making accurate visual identification of the spider necessary. The most widely cited feature is the distinctive dark marking on the cephalothorax, which is the fused head and chest section of the body. This marking is often described as a “violin” or “fiddle” shape, with the neck pointing toward the rear of the body. However, the intensity of this marking can vary, and it is not always a definitive identifier, as other harmless spiders can have similar patterns.
A more reliable characteristic, though harder to see, is the unique eye arrangement of the brown recluse. Most spiders possess eight eyes arranged in two rows, but the brown recluse has only six eyes. These six eyes are arranged in three pairs (dyads), with one pair positioned centrally and the other two pairs on either side. This specific eye configuration, combined with the lack of distinct color patterns on the legs and abdomen, is the most certain way to confirm a sighting.