Cellar spiders are a common sight in many homes, often found discreetly occupying quiet corners. These arachnids, belonging to the family Pholcidae, are known for their unassuming presence. This article details their visual characteristics, from overall body structure to the features that distinguish them from similar-looking arachnids.
Defining Physical Characteristics
Cellar spiders have small, oval-shaped bodies that are translucent. Their bodies are divided into two segments: the cephalothorax (fused head and thorax) and the abdomen. Female long-bodied cellar spiders have a body length ranging from 7 to 8 millimeters, while males are slightly smaller, around 6 millimeters long. Some short-bodied species are even smaller, with female bodies around 2 millimeters and males about 1.6 millimeters.
Their most striking feature is their eight long, slender legs, disproportionately long compared to their small bodies. These legs can be five to six times the length of their body, with front legs of long-bodied species reaching up to 45-50 millimeters. The legs are covered in fine, grey bristles and may have subtle pale and dark bands at the joints.
Their coloration ranges from pale yellowish to light brown or grey. Some species exhibit a dark spot on the back of the cephalothorax or blurred dark spots on the dorsal side of the abdomen. The head area around their eyes is slightly darker.
Cellar spiders possess eight small eyes. These eyes are arranged in a specific pattern: two eyes are located in the center of the face, with three eyes clustered on each side, forming widely spaced lateral groups. This eye arrangement distinguishes them from some other spider families.
Identifying Features and Look-Alikes
Cellar spiders exhibit a posture and visual defensive behavior that aids identification. When at rest, they hang upside down within their webs. If disturbed, cellar spiders rapidly vibrate or bounce their bodies, causing their entire web to shake. This movement blurs their outline, making them less visible.
The webs spun by cellar spiders are another visual cue, characterized by their irregular, loose, and tangled appearance. Unlike some other spiders that consume old webs, cellar spiders layer new silk on top of existing structures, leading to a noticeable accumulation of messy cobwebs. These webs are found in corners of rooms, ceilings, or other undisturbed, damp areas.
Cellar spiders are mistaken for other arachnids, particularly harvestmen, also called “daddy longlegs.” A key distinction lies in their body structure: cellar spiders, as true spiders, have two clearly separated body segments—the cephalothorax and the abdomen—connected by a narrow “waist.” Harvestmen, in contrast, have a single, fused, oval-shaped body that appears as one unit, with no distinct separation between the segments. Harvestmen do not spin webs, unlike cellar spiders. While some house spiders may also be found indoors, cellar spiders generally have significantly longer and more delicate legs relative to their body size compared to most house spiders.