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.