Spiders that appear predominantly white or off-white are found across various species, utilizing this coloration for distinct purposes in their natural environments. This pale hue often plays a role in their survival strategies.
Common White Spider Species
Among the most commonly encountered white spiders are those belonging to the Thomisidae family, known as crab spiders. These spiders, such as the goldenrod crab spider (Misumena vatia), are frequently found on flowers where they lie in ambush for prey. Their bodies are often broad with a bulbous abdomen, and their first two pairs of legs are noticeably thicker and longer, often held in a crab-like posture.
Sac spiders can also appear white, particularly certain species often referred to as yellow sac spiders. They are relatively small and possess long, slender legs, with the front pair being longer than the others. Unlike many spiders, sac spiders do not build webs for hunting but are nocturnal hunters that construct small silk sacs for shelter and egg-laying, often found in corners of homes or gardens.
Nursery web spiders can also exhibit a pale or whitish coloration, though their color is variable. These spiders are slender with a cigar-shaped body and long, robust legs. They are active hunters found in tall grasses, along wooded edges, and in various vegetation. They are distinguished by the female’s unique behavior of carrying a spherical egg sac in her jaws and later building a silken “nursery” web for her young.
Certain jumping spiders can also be predominantly white or have significant white markings. Jumping spiders are generally small to medium-sized, with compact bodies and large, forward-facing eyes that provide excellent vision for their active hunting style. They are daytime predators that do not spin webs to catch prey but instead stalk and pounce, using silk as a safety line.
The Science Behind Their Color
The white coloration observed in some spiders is primarily a form of camouflage, allowing them to blend into their surroundings to ambush prey or avoid predators. This adaptation is common in species like crab spiders that reside on flowers, where their white bodies make them invisible against petals. Some species, such as the goldenrod crab spider, can change their color between white and yellow to match the flowers they inhabit, a process that can take several days.
The mechanism behind this white appearance and color change involves specialized components. White coloration in spiders often results from the presence of guanine crystals, stored in specialized cells beneath the spider’s outer layer. These crystals scatter and reflect light, producing a matte white or silvery appearance depending on their shape and arrangement. In color-changing spiders, pigments like carotenoids can be transferred to the hypodermis, overlying the guanine layer, to produce yellow or other hues. This combination of structural color from guanine and the presence or absence of pigments allows for their disguise.
Are White Spiders Dangerous?
The presence of white spiders often raises concerns, but most species are not considered medically significant to humans. While nearly all spiders possess venom to subdue insect prey, the venom of most white spiders is typically not potent enough to cause serious harm to humans. Bites are generally uncommon and occur only when a spider feels threatened or is accidentally trapped against the skin.
Sac spiders are among the few white or pale-colored spiders whose bites can be painful and cause localized symptoms. A bite from a sac spider can cause immediate stinging pain, followed by redness, swelling, and a burning sensation at the site. A small blister or lesion may develop, though serious complications like necrosis are rare and often linked to secondary infections rather than the venom itself. If bitten, cleaning the area with soap and water and applying a cold compress can help alleviate symptoms, and medical attention should be sought if symptoms worsen or persist.
Key Identification Features
Distinguishing between different white spider species involves observing characteristics beyond just their color. Body shape offers important clues; crab spiders, for example, often have a flattened or broad body with a bulbous abdomen. In contrast, sac spiders tend to have a more slender, elongated body, while nursery web spiders have a streamlined, cigar-shaped body.
Leg Characteristics
The arrangement and thickness of a spider’s legs also provide distinguishing features. Crab spiders are recognized by their two front pairs of legs being thicker and longer than the others, held in a distinctive crab-like posture. Sac spiders possess long, delicate legs, with their front pair often being longer. Nursery web spiders have long, robust legs, which they frequently hold outstretched in front of them.
Hunting Strategy and Web Use
A spider’s hunting strategy and presence or absence of a web can also aid identification. Many white spiders, such as crab spiders and sac spiders, are active hunters that do not build webs to catch prey, instead relying on ambush or pursuit. Nursery web spiders, while also active hunters, are known for constructing a silken nursery tent for their young.