Spiders
Little Miss Muffet might have been frightened away, but a world without spiders would be a disaster for humanity! Spiders are nature's ultimate pest controllers. Let's spin a web of knowledge and explore what makes these 8-legged predators so incredible!
The Ultimate Insect Hunters!
No! They are completely different animals! They are actually called Harvestmen. Unlike true spiders, they only have one combined body part, they have no venom, no fangs, and they cannot spin silk.
They don't chew at all! Spiders use "external digestion." They spit digestive juices onto their prey to liquefy it, and then their sucking stomach pulls the liquid food directly into their bodies.
Test Your Arachnid Instincts
Spiders are built very differently than the bugs they hunt. Pick an answer below to test your biological knowledge.
They shed it completely! This process is called molting. Because their exoskeleton is a hard shell, it cannot grow with them, so they must leave the old one behind like an empty suit of armor.
They use hydraulic pressure! Spiders don't move their legs with regular muscles like we do. Instead, their heart pumps blood into their legs to force them straight!
The Anatomy of a Hunter
Tap each card to uncover the unique anatomy and specialized adaptations that make spiders the top predators of the insect world.
Key Concepts
Not an Insect
Tap to learn moreSpiders are completely different from insects! Insects have 6 legs, 3 body parts, and antennae. Spiders have 8 legs, only 2 body parts (the cephalothorax and abdomen), and no antennae.
The Exoskeleton
Tap to learn moreSpiders do not have bones inside their bodies like humans do. Instead, they are supported and protected by a hard outer shell called an exoskeleton.
Molting
Tap to learn moreBecause their exoskeleton is a hard shell, it does not grow with them. As the spider grows, it must completely shed its old skin (molt) and emerge with a larger, softer one that hardens over time.
Spinning Silk
Tap to learn moreAll spiders have organs called spinnerets on the underside of their abdomen. The silk comes out as a liquid, but the moment it hits the air, it polymerizes (turns into a solid, natural plastic string).
Hydraulic Legs
Tap to learn moreSpiders don't move their legs with internal muscles the way mammals do. Instead, their heart pumps their legs full of blood to straighten them out, acting exactly like a hydraulic machine.
External Digestion
Tap to learn moreSpiders inject prey with venom using their fangs, then spit digestive juices onto the prey. This liquefies the insect's insides so the spider's sucking stomach can drink it like a smoothie.
Strict Meat-Eaters
Tap to learn moreOut of the tens of thousands of spider species in the world, virtually none of them eat plants or vegetables. They are pure predators that hunt and eat other animals.
Ecosystem Guardians
Tap to learn moreSpiders are the number-one predator of insects. If spiders went extinct, insects would rapidly overpopulate and eat all the plants and crops on Earth, causing a global disaster.
Interactive: Arachnid Anatomy Visualizer
Select a body part to scan the spider and learn how its unique anatomy functions.
Apply Your Knowledge
Let us see if you can correctly identify the essential biological terminology associated with arachnids.
Match the Concepts
Click a biological term to select it, then click the matching description to place it.
Real-World Challenge
Imagine you are an arachnologist (a spider scientist) exploring a jungle. You find a small creature with a hard exoskeleton spinning a thread of silk from its mouth. You count three distinct body segments and exactly six legs. Based on the rules of anatomy you just learned, is this creature a spider or an insect? Defend your answer using three distinct pieces of anatomical evidence.
What Has Changed Since This Episode Aired
This episode originally aired in 1996. Since then, the science of arachnology and bio-engineering has advanced significantly!
Updated: In the episode, Bill Nye marvels at how liquid silk polymerizes into a natural plastic. Today, scientists are actively bio-engineering synthetic spider silk because it is proportionally stronger than steel and incredibly flexible. They are trying to mass-produce it to make lightweight bulletproof vests and strong medical sutures for surgeries!
Updated: The episode points out that very few spiders are dangerously poisonous to humans. Now, researchers are actually using spider venom to save lives. Specialized compounds found in tarantula and funnel-web spider venom are currently being tested to create eco-friendly agricultural pesticides and even non-addictive painkillers for humans!
Updated: The expert in the episode stated there were about 35,000 spider species in the world. Arachnologists have been busy exploring since then! As of today, the World Spider Catalog recognizes over 50,000 distinct, officially categorized species of spiders across the globe.
Test Your Understanding
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Episode Discussion
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