True, bright white coloration is uncommon in the arachnid world. Many spiders that appear pale are actually translucent, cream, or faint yellow. The few species that exhibit a truly white color do so for specialized reasons, usually connected to ambush predation. Understanding the biology behind the color is the first step in identifying these creatures.
The Most Common White Spiders
The most commonly encountered truly white spiders belong to the Thomisidae family, known as flower or crab spiders. The female Goldenrod Crab Spider (Misumena vatia) is the most recognizable example, displaying a bright white body with a bulbous abdomen and two pairs of noticeably longer front legs. These ambush predators do not spin a web, instead lying in wait on white flowers like daisies or Queen Anne’s lace.
Their crab-like shape and ability to walk sideways allow them to maneuver effectively on blossoms, waiting motionless for pollinators. Females are significantly larger than males and are capable of the dramatic color change that aids their camouflage. Their venom subdues large insects like bees and butterflies but is harmless to humans.
Yellow Sac Spiders (Cheiracanthium) are frequently mistaken for white spiders. While typically pale beige, cream, or light yellow, some individuals, especially juveniles, appear white. These active, nocturnal hunters do not build webs. Instead, they create small, flat silken sacs in sheltered spots, such as ceiling corners or under leaves, where they rest during the day.
Ghost Spiders (family Anyphaenidae) are characterized by their pale, translucent, or yellowish-white bodies. These spiders are active, fast-moving hunters, often seen scurrying across walls or foliage at night. They are not web-builders, but they construct silk retreats in crevices or under bark for resting and egg-laying. Ghost spiders are generally small, typically ranging from 5 to 10 millimeters in body length.
Why Spiders Use White Coloration
The white appearance is a highly refined adaptation used primarily for crypsis, or camouflage, especially by ambush hunters. For flower-dwelling crab spiders, the bright white color allows them to blend perfectly into light-colored flower petals, rendering them invisible to approaching insect prey. This offensive tactic dramatically increases their hunting success.
The mechanism for white coloration often involves specialized cells within the spider’s body. The white color is frequently structural, caused by the storage of guanine crystals in cells beneath the cuticle. Guanine, a waste product, is crystallized in these specialized cells, which scatter incident light to produce a bright, matte white or silvery appearance.
In species like the Goldenrod Crab Spider, this guanine layer provides a white background against which other pigments can be deployed or removed. The spider can actively change its color from white to yellow over several days or weeks by synthesizing or breaking down a yellow ommochrome pigment. This morphological color change enables the spider to match the color of its current flower habitat.
Safety and Identification of Pale Spiders
The majority of common white spiders, such as Flower Crab Spiders and Ghost Spiders, are not considered a threat to humans. Their fangs are generally too small or their venom too mild to cause more than localized, temporary irritation if a bite occurs. However, relying on color alone for safety assessment is unreliable, as many medically significant spiders have pale stages or variations.
The Yellow Sac Spider is the most notable exception among pale spiders and is often cited as the cause of most indoor human-spider interactions. Their bite is medically significant, capable of causing localized pain, swelling, and sometimes a necrotic lesion that is less severe than a Brown Recluse bite. Identification should focus on their distinctive long front legs and their habit of building a silken sac in wall-ceiling corners.
To properly identify a pale spider beyond its color, observe specific anatomical details and behavior cues. Look for the spider’s eye arrangement, a definitive identifier for most families, or the presence or absence of a web. Crab spiders have a wide, crab-like body and hold their long front legs out to the side. Ghost Spiders are slender, very fast runners with long spinnerets at the tip of the abdomen.