Clubionidae

Common Name

Sac Spiders

Overview

The family Clubionidae, commonly referred to as sac spiders, includes a diverse group of hunting spiders known for their unique silken retreats or "sacs," which they craft as daytime hiding places or as protective shelters for their egg sacs.

Taxonomy

• Kingdom : Animalia
• Phylum : Arthropoda
• Class : Arachnida
• Order : Araneae
• Family : Clubionidae

Key Characteristics

• Medium-sized spiders, usually ranging from 4 to 12 mm in length.
• Cylindrical or slightly flattened body shape.
• Pale coloration, often creamy, yellow, or light brown.
• Eight eyes arranged in two horizontal rows.
• Chelicerae (mouthparts) are vertical, not crossing.
• Spinnerets (silk-producing organs) are often visible and prominent.

Life Cycle

• Egg stage : Laid in silken sacs.
• Spiderling stage : Hatch from eggs and undergo several molts before reaching maturity.
• Adult stage : Engage in solitary hunting, either at night or day depending upon species.

Behavior and Ecology

• Primarily nocturnal hunters.
• Craft silken retreats in foliage, under bark, or within leaf litter for daytime concealment.
• Prey mostly on insects and other small arthropods.
• Not web-weavers; rely on agility and silk retreats rather than webs for survival.
• Often found in domestic environments, particularly houses, gardens, and forests.

Notable Species

• Clubiona corticalis : Often found under bark.
• Clubiona trivialis : Common in low vegetation.
• Clubiona japonica : Noted for its distinctive reddish-brown coloration.

Conservation

• Most species are not threatened.
• Some habitat-specific species may be impacted by deforestation and habitat loss.

Significance to Humans

• Generally beneficial as control agents for pest insects.
• Some species may wander into homes, potentially causing mild bites which are typically not dangerous.
• Useful subjects for studying arachnid behavior and silk utilization.

Fun Facts

• Silk Craftsmanship : Unlike orb-weavers, sac spiders use their silk exclusively for crafting retreats and egg sacs.
• Night Stalkers : Many sac spiders are more active at night, hunting prey under the cover of darkness.
• Color Shifts : Some species of sac spiders can change color, blending in with their environment for better camouflage.
• Nocturnal Noms : These spiders often leave their silken retreats at night to hunt, returning at dawn.