A spider web is both a home and a trap, engineered from a protein fibre produced inside the animal's own body. The orb web covered in morning dew is a familiar sight, but spiders build many kinds of silk structures and use silk for much more than catching prey.
Key takeaways
- Spider silk is a protein fibre made in special glands and pushed out through spinnerets.
- A single spider can make several types of silk for different jobs.
- Not all spiders build webs, and webs come in several designs.
- Spiders avoid sticking by using non-sticky threads, special leg features and careful movement.
- Silk is very strong for its weight, but claims that it beats steel in every way are oversimplified.
How silk is made
Inside a spider's abdomen are silk glands that store a liquid protein. When the spider pulls the silk, the liquid is drawn through narrow ducts and out of finger-like organs called spinnerets. As it passes through, the proteins align and solidify into a fine thread. Orb-weaving spiders can produce up to seven kinds of silk, each with different properties, for building frames, sticky capture threads, wrapping prey, protecting eggs and making dragline safety lines.
Types of webs
The classic orb web has radiating spokes and a spiral of sticky thread. Other spiders build tangled cobwebs, funnel webs, sheet webs or dome shapes. Many spiders, such as wolf spiders and jumping spiders, do not build webs to catch prey at all. They hunt by sight or ambush, though they still use silk for draglines, egg sacs and shelters.
Building an orb web
An orb-weaver often starts by letting a thread drift on the breeze until it sticks to something. The spider strengthens this bridge, adds more lines to form a frame and spokes, then lays a temporary spiral. Finally, it replaces that spiral with sticky capture thread, eating the temporary threads as it goes. Many orb weavers rebuild or repair their webs every day.
Why spiders don't get stuck
Spiders have a few advantages. They use non-sticky threads for the spokes and walk along those. Their legs have tiny hairs and claws that limit contact with sticky strands, and a light oily coating may reduce adhesion. They also move carefully, touching the web at few points. A spider can still become stuck in the wrong parts of a web, but it usually avoids them.
How strong is silk?
By weight, some spider silks are impressively strong and also very stretchy, which lets a web absorb the impact of a flying insect. Comparisons with steel depend on how strength is measured: silk is strong relative to its weight, but a steel rod of the same thickness is stronger overall. Researchers study spider silk as inspiration for new materials, though producing it at scale is difficult.
Are spiders harmful?
Most spiders are harmless to people and help control insect numbers. A small number have medically significant bites. If you are bitten and feel unwell, seek local medical advice.
How spiders sense the world
Most spiders have eight eyes, but vision is not always their main sense. Web-building species rely on vibrations. Their legs have tiny slit-shaped organs and fine hairs that detect movement in the web, so a spider can tell the difference between a trapped insect, a struggling beetle and a falling leaf, and can even sense the size of the prey. Jumping spiders are the exception. They have excellent eyesight, with a large pair of forward-facing eyes that give sharp, colour-sensitive vision, and they stalk and pounce on prey like tiny cats.
Silk beyond webs
Silk is useful in many ways. Spiders trail a dragline behind them as a safety rope, and if they fall they can climb back up. Many wrap their eggs in silk sacs, and some mothers guard or even carry the sac. Trapdoor spiders use silk to line burrows and make hinged lids, and some water spiders build a silk bell underwater that they fill with air. Male spiders of some species wrap a gift of prey in silk before mating. Young spiders can balloon, releasing silk threads to be carried on the wind, sometimes travelling long distances.
A huge and varied group
More than fifty thousand species of spider have been described, and new ones are still being discovered. They range from tiny species smaller than a pinhead to large tarantulas with legs spanning several centimetres. Some live in burrows, others on plants, in caves or near water. Spiders are arachnids, a group that also includes scorpions, mites and ticks, and they are not insects, which have six legs and usually wings. Almost all spiders are predators, and they eat vast numbers of insects.
Safety and living with spiders
Few spiders are dangerous to people. Species with medically significant venom include the Sydney funnel-web in Australia, black widows and recluse spiders in the Americas. Bites are uncommon and serious outcomes are rare, especially with access to modern medical care. If you are bitten and feel unwell, seek medical advice, and if possible note what the spider looked like. House spiders can be moved outside with a cup and card, and keeping them helps reduce flies and other pests.
Spider silk research
Because silk combines strength and stretch, scientists are interested in using it as a model for new materials. Researchers have engineered bacteria, yeast and other organisms to produce silk-like proteins, and spinning them into fibres that behave like natural silk is a challenge. Potential uses include medical sutures, protective fabrics and lightweight composites, and some products are already on the market, though it is difficult to match the properties of real silk at large scale.
Frequently asked questions
Do spiders eat their webs?
Many orb weavers recycle old silk by eating it, which lets them reuse the protein.
Can all spiders make silk?
Almost all spiders produce silk in some form, though not all use it to make capture webs.
How do baby spiders travel?
Many young spiders climb up high and release a silk thread to catch the wind, a behaviour called ballooning.
Do spiders have bones?
No. Spiders have an exoskeleton, a tough outer covering that supports and protects the body. As they grow, they shed it in a process called moulting, and a new, larger one hardens in its place.
How many legs and eyes do spiders have?
All spiders have eight legs. Most have eight eyes, but the number varies from six to none, depending on the species, and cave-dwelling spiders may be nearly or completely blind.
Are spiders insects?
No. Spiders are arachnids. They have eight legs and two main body parts, while insects have six legs and three body parts. Spiders also do not have antennae or wings.
Sources and further reading
Written by
FactNest Editorial Team
FactNest is operated by Muonix. The FactNest Editorial Team publishes general-interest explainers with AI-assisted drafting and illustrations. Contact contact@muonix.co for questions or corrections; we respond within 2 business days.
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