1. Classification & Appearance

Feature Description

Family Araneidae (Orb-Weaving Spiders)

Size Highly variable. Females are generally medium to large (often 5 mm to 20 mm body length). Males are much smaller.

Body Shape Typically have a large, rounded, or oval abdomen that is conspicuously larger than the cephalothorax (head). They often have stout, hairy, or spiny legs.

Colour & Markings Extremely diverse. Many are drab (brown, grey) to blend in with bark or foliage, but many species (like the Argiope or Marbled Orb Weaver Araneus marmoreus found in Alberta) are brightly coloured with yellow, orange, or white patterns.

Eyes Eight similar eyes, usually arranged in two rows of four. They have relatively poor eyesight compared to hunters like Jumping Spiders, relying instead on vibrations.

2. The Orb Web (Their Defining Feature)

Orb weavers are defined by the intricate, geometric, wheel-shaped web they construct:

• Structure: The web consists of radial strands (non-sticky silk spokes) and a dense, sticky capture spiral (concentric circles) that traps flying prey.

• Engineering: Web construction is a methodical feat that starts with the spider floating a silk line on the wind to catch an anchor point. Once the frame is built, the spider lays down the dry, non-sticky radial spokes, and then spins the final, sticky spiral inward.

• Daily Rebuilding: Most orb weavers are nocturnal and build a new web almost every evening. This is a highly efficient behavior:

  • They consume the old web (including trapped insects and debris) to recycle the silk proteins, which are energetically costly to produce.

  • This ensures the web's capture silk remains fresh and sticky, as effectiveness degrades quickly from dust and environmental wear.

• Habitat: Webs are built in open spaces where flying insects are abundant, often strung between tree branches, shrubs, garden plants, or near porch lights.

3. Hunting and Diet

• Hunting: The spider typically rests head-down in the center of the hub or hides in a nearby silk retreat connected by a silk "trapline."

• Prey Detection: They detect prey by monitoring the vibrations traveling through the sticky silk strands.

• Prey Subdual: Once an insect is caught, the spider rushes out, delivers a quick venomous bite to paralyze the prey, and then rapidly wraps it in copious amounts of silk before either consuming it or hanging it for later.

• Diet: Primarily flying insects like flies, mosquitoes, gnats, moths, and sometimes larger prey like grasshoppers.

4. Life Cycle

• Sexual Dimorphism: Extreme. Males are significantly smaller and drabber than the females.

• Mating: Males wander in search of a mate and perform a unique courtship ritual, often involving vibrating or "plucking" the female's web to announce their intentions and avoid being mistaken for prey.

• Sexual Cannibalism: Males often face a high risk of being attacked and cannibalized by the much larger females, especially after mating.

• Egg Sac: Females lay large clutches of eggs (often hundreds) encased in a dense, fluffy, silken egg sac in the late summer or fall. This sac is typically attached to vegetation near the web or hidden in a protected location.

• Overwintering: In cold climates like Alberta, the adult female usually dies after laying her last egg sac in the autumn. The eggs survive the winter inside the protective sac and hatch the following spring.

• Lifespan: Most temperate species complete their life cycle in about one year.

5. Interaction with Humans

• Toxicity: Orb weavers are venomous, but their venom is not considered medically significant to humans.

• Bite Risk: They are extremely docile and non-aggressive. A bite is rare and defensive, typically resulting in only mild, local pain, similar to a mosquito bite or bee sting.

• Ecological Role: They are highly beneficial predators in gardens and ecosystems, providing natural control of insect pests.