Few spiders are truly a pure, opaque white; most species described this way are actually pale, translucent, or light-colored. Those that are white typically use the coloration for specialized camouflage. Understanding which spiders fit this description requires examining their behavior and body structure. This article focuses on the most frequently encountered species described as white.
The Primary Identification: Flower Crab Spiders
The spiders most accurately described as genuinely white are the Flower Crab Spiders, primarily belonging to the family Thomisidae. These arachnids, such as Misumena vatia, are unique because their color is a deliberate adaptation for hunting. They rely on an ambush strategy that requires perfect concealment on flowers, as they are not web-builders for prey capture.
Their name comes from their distinct, crab-like appearance, featuring a flattened body and holding their two front pairs of legs out to the side. These powerful front legs are used to grasp prey, and they are capable of moving sideways and backward, much like a crab. The white coloration is often achieved by storing guanines, which are waste products, in specialized cells beneath the exoskeleton.
A remarkable characteristic of the female is the ability to change color between white and yellow to match the flower they are hunting on. This chromatic adaptation is not instantaneous; it can take several days to synthesize and deposit a yellow pigment. This ability allows them to remain hidden from unsuspecting pollinators like bees and butterflies, which they subdue with venom.
Other Pale Spiders Mistaken for White
Beyond the specialized Flower Crab Spiders, several other common species are frequently mistaken for being white, though their coloration is typically light cream, translucent, or pale yellowish-tan. Two prominent groups that fit this description are Ghost Spiders and pale Sac Spiders. These spiders are active hunters, meaning they actively pursue prey rather than waiting in a web.
Ghost Spiders (Family Anyphaenidae) are generally light-colored, which contributes to their common name, and they are primarily nocturnal. They use small silken retreats or sacs for resting during the day in sheltered locations, such as under bark or in folded leaves.
Sac Spiders, particularly species from the genus Cheiracanthium, are also pale, often a yellow or beige-white, sometimes with a faint greenish tinge. These spiders are frequently found indoors, using small, dense silk tubes or sacs in corners or along ceilings as a protective shelter. They emerge at night to hunt for insects, making them one of the most common spiders encountered by humans inside structures.
Understanding the Bite Risk
The medical relevance of pale spiders encountered by the public is generally low. Flower Crab Spiders are considered medically insignificant to humans; while they possess venom to subdue large insect prey, they rarely bite people. A bite from a Flower Crab Spider usually results only in minor, localized irritation or redness at the site.
Sac Spiders, however, are associated with a greater likelihood of biting defensively, often when they become accidentally trapped against a person’s skin, such as inside bedding or clothing. The bite of a Sac Spider is typically described as causing a sharp, stinging pain, often followed by local swelling and redness. While historical reports sometimes linked these bites to severe necrotic wounds, modern medical consensus suggests that such severe outcomes are extremely rare and often result from secondary bacterial infection rather than the venom itself.
If a bite occurs, the standard guidance is to clean the area thoroughly with soap and water and apply a cold compress to reduce swelling. Over-the-counter pain relievers or antihistamines can help manage discomfort and any minor allergic reaction. Seeking medical attention is recommended if swelling spreads significantly, if signs of infection develop, or if systemic symptoms like fever or nausea appear.