Sac Spider

Sac spiders are named for the distinctive small, tube- or sac-shaped silk retreat they construct rather than a typical prey-capturing web. This retreat is often tucked into a curled leaf, a fold in bark, a corner between a wall and ceiling, or another sheltered nook, and serves as a resting and molting shelter rather than a trap for prey.

Most species, such as those in the widespread genus Cheiracanthium, are pale yellow, tan, or greenish in overall color with a slightly darker head region, giving them a simple, uniform appearance without the bold patterns seen in many other spider families. They are active, free-roaming hunters at night, leaving their silk retreat to search for prey on foliage or indoors.

Sac spiders are found on every inhabited continent and are frequently encountered both outdoors in gardens and vegetation and indoors, where they may take shelter in corners, behind picture frames, or in folded fabric.

• Slender body, uniformly pale yellow, tan, or light green with a slightly darker head region
• Long, thin legs relative to body size, giving an overall delicate appearance
• Constructs a small silk sac retreat rather than a capture web, often in a curled leaf or wall corner
• Eight eyes arranged in two rows typical of the family
• Lookalikes include other pale-colored roaming spiders, but the tubular silk retreat and uniform coloring help distinguish sac spiders

Sac spiders are found in gardens, meadows, and woodland edges, often within rolled or folded leaves, and are equally common indoors, sheltering in ceiling corners, behind furniture, or in folds of curtains and clothing. They occur across temperate and subtropical regions worldwide, with several Cheiracanthium species now cosmopolitan through incidental transport by humans.

Rather than trapping prey in a web, sac spiders are active nocturnal hunters that leave their silk retreat after dark to search vegetation or indoor surfaces for small insects, which they overpower and consume. During the day they retreat to their silk sac to rest and molt, often reusing or repairing the same retreat multiple times. Their willingness to shelter in human structures makes them one of the more frequently encountered indoor spiders in many regions.

Females construct a flattened silk egg sac, often within their own retreat, and may guard it until spiderlings emerge. Spiderlings disperse to build their own small sac retreats and begin hunting small prey independently. Development to maturity takes place over several months through successive molts, and in temperate climates sac spiders commonly overwinter as immature juveniles within sheltered retreats.