Cellar spiders are a common sight in many homes, often found in undisturbed areas like basements, attics, and corners of rooms. Their distinctive appearance frequently prompts questions regarding their actual size. These arachnids, while appearing large due to their elongated limbs, are generally considered harmless inhabitants of our indoor spaces.
Measuring Cellar Spider Dimensions
When considering the size of a cellar spider, two key measurements are typically referenced: body length and leg span. Body length is measured from the front of their cephalothorax to the end of their abdomen. The most widespread species, the long-bodied cellar spider (Pholcus phalangioides), has a relatively small body.
Females typically have a body length ranging from 7 to 8 millimeters (1/4 to 5/16 of an inch). Males are usually slightly smaller, around 6 millimeters (1/4 of an inch). Their impressive leg span makes them seem larger, as their legs can be five to six times the length of their body. For female long-bodied cellar spiders, front legs alone can measure 45 to 50 millimeters (1 3/4 to 1 15/16 inches), meaning their total leg span can reach over 2 inches.
Factors Affecting Cellar Spider Size
Not all cellar spiders are identical in size, and several factors contribute to these variations. One significant reason is the existence of different species within the Pholcidae family, which includes about 20 types in the United States and Canada. While the long-bodied cellar spider is prevalent, some “short-bodied” species have much smaller bodies (1.6 to 2 millimeters) and legs (8.5 to 9.5 millimeters).
The sex of the spider also plays a role; females are generally slightly larger than males. A spider’s age influences its size, with juveniles being considerably smaller than mature adults. It takes approximately one year for a spiderling to develop into a full-sized adult. Environmental elements, such as food availability, can also impact growth, with well-fed individuals tending to achieve larger sizes.
Distinguishing Cellar Spiders from Other Species
Their long, thin legs often lead to confusion with other arachnids, particularly harvestmen, also known as “daddy longlegs.” However, cellar spiders are true spiders with two distinct body segments (cephalothorax and abdomen). Harvestmen have a single, unified, oval-shaped body and do not spin webs, unlike cellar spiders who create messy, irregular webs.
Their bodies are typically small and oval-shaped, ranging in color from pale yellowish to light brown or gray, with exceptionally delicate legs. A notable behavior is their tendency to vibrate rapidly in their web when disturbed, blurring their outline and making them difficult for predators to target. This action has earned them the alternative name “vibrating spiders.” They often hang upside down in their loose, non-adhesive webs, which they continuously expand rather than rebuilding.