1. Classification & Appearance

Feature Description

Family Cheiracanthiidae (sometimes placed in Miturgidae)

Size Small to medium. Typically 3 mm to 10 mm body length.

Colour Pale, yellowish, straw-colored, or green-tan. They often have a slightly darker, reddish-brown spot at the tip of the abdomen and dark-tipped mouthparts (chelicerae).

Body Shape Slender body with long, spindly legs. The front pair of legs is noticeably longer than the other three pairs, which they use for reaching and grappling prey.

Movement Quick and agile runners. They can move equally well backward and forward.

2. Hunting and Habitat

• Hunting Method: Yellow Sac Spiders are active hunters and vagrants (wandering spiders). They do not build large webs to trap prey.

• Activity: Primarily nocturnal (active at night), leaving their retreats to forage for prey.

• Diet: Generalist predators, feeding on a wide variety of small insects and other arthropods. Outdoors, they are highly beneficial in gardens as they prey on agricultural pests like aphids and caterpillars.

• Habitat:

  • Outdoors (Native C. inclusum): Trees, shrubs, foliage, and garden plants.

  • Indoors (Introduced C. mildei): Often found high up near the ceiling, along wall/ceiling corners, or behind picture frames. They are common in homes, garages, and sheds, especially in the fall when seeking warmer shelter.

3. Silk Use (The Sac)

• Prey Capture Webs: NO. They do not use silk to catch food.

• The Retreat Sac: YES. They construct a distinctive, small, tough, silken tube or sac that is about the size of a thumb or smaller. This sac is their retreat for resting during the day, molting, and laying eggs.

  • The sac is usually found in a protected location, such as in a corner, along a ceiling line, under a leaf, or tucked into a cluster of fruit.

4. Life Cycle

• Mating: The male performs a tactile courtship dance involving touching and vibrating the female's body.

• Egg Sac: The female lays her eggs inside her silk retreat sac and either seals herself inside with the eggs or guards them closely from the outside. The sac is usually suspended in a protected spot.

• Parental Care: The mother spider remains near the egg sac and actively guards it until the spiderlings hatch and disperse.

• Lifespan: They typically live for one to two years.

5. Interaction with Humans (The Bite Question)

The Yellow Sac Spider has historically been one of the most frequently named spiders responsible for bites indoors.

• Bite Risk: They are more likely to bite defensively than many other house spiders because they are active wanderers and may come into accidental contact with humans while foraging at night. Most bites occur when the spider is unintentionally trapped in clothing, towels, bedding, or gloves.

• Toxicity and Symptoms:

  • Venom: Their venom is primarily neurotoxic and cytotoxic (cell-damaging), but generally NOT medically severe to humans.

  • Symptoms: A bite typically feels like a sharp pinprick followed by localized pain, redness, and swelling. Sometimes, a persistent blister may form at the site. Symptoms generally resolve within 7 to 10 days.

  • Note: While older studies linked this spider to necrotic tissue damage, most modern medical and arachnological sources strongly dispute this link for these species, especially the C. mildei commonly found in homes. The majority of tissue damage attributed to spiders is actually caused by bacterial infections (like MRSA) or other non-spider causes.