spectacular spiders

Spiders are often-misunderstood arachnids. Learning facts about these fascinating creatures may help us all appreciate them.

• Spiders evolved 386–200 million years ago, making them truly ancient beings.
• There are nearly 50,000 spider species globally, with about 3,000 in the U.S.Overwintering & Native Species
• All species of spiders native to Pennsylvania overwinter, often in leaf litter (another great reason to “leave the leaves”).

Anatomy & Physiology

• Most spiders are venomous, but not in a way dangerous to humans—any creature with fangs produces venom.
• They have eight legs, eight eyes, and two body parts: the cephalothorax and abdomen.
• Spiders have the most centralized nervous system of any arthropod.
• They don’t have muscles in their legs—movement is hydraulic, which is why legs curl inward when they die.
• Spiders cannot eat solid food. Instead, they digest, regurgitate, and re-ingest until only the exoskeleton remains (often left behind in webs).

Silk, Spinnerets, & Webs

• Spiders can produce up to eight types of silk and typically have six spinnerets, the organ that produces the silk.
• Webs often combine multiple types of silk—sticky threads for catching prey and non-sticky borders for movement.
• Only about 50 percent of spider species build webs. Others create hang lines, lassos, nets, or even “sleeping bags.”
• Silk is protein-intensive; web building is energetically expensive.
• Non-web builders, like wolf spiders, are active hunters.

Species Notes

• Common PA spiders include: Grass Spiders, Wolf Spiders, Jumping Spiders, Crab Spiders, Orbweavers, Fishing Spiders, Cellar Spiders, Black Widows, and the non-native Brown Recluse.
• Fishing Spiders are semi-aquatic. They can walk on water and breathe underwater using air pockets.
• Orbweavers is the largest group of web builders. They rebuild and reabsorb their webs daily and keep them remarkably tidy.
• Crab Spiders are often found on flowers and can change color for camouflage.
• Black Widows are “shy,” rarely leave their webs or biting humans.
• Grass Spiders build sheet-like, non-sticky webs and rely on speed to catch prey.
• Jumping Spiders can leap up to 50 times their body length. One species in this family feeds its young a milk-like liquid, while another mimics ants to catch prey.
• Only one known non-predatory species exists, the Bagheera kiplingi, which is a plant-eating, jumping spider that feeds on acacia buds and nectar. (It is rare and not native to PA._
• Only three spider families lack venom (and therefore fangs): Uloboridae (cribellate orb-weavers), Holarchaeidae, and Mesothelae (venom vestigial or disputed).

Behavior & Ecology

• Spiders are among the most effective natural pest controllers—eating more mosquitoes than bats and birds combined.
• “Daddy longlegs” are not spiders at all, but Harvestmen (order Opiliones). They have a single, fused body segment and eat solid foods, unlike spiders.

Culture, Fear, & Research

• Arachnophobia is the fifth most common fear in the U.S., especially among people of European descent.
• Historical fear is tied to beliefs that spiders spread disease and to past episodes of mass hysteria.
• Spiders feature in mythology worldwide as weavers of destiny, creators of the universe, and bringers of light.
• They’ve been subjects in scientific studies, including experiments on how drugs like LSD, caffeine, and marijuana affect web-building.
• Jumping spiders are frequently studied for their movement and remarkable visual systems.