Watch a garden spider build an orb web and the first thing that stands out is the waste. She spins a frame, fills it with radial spokes, adds a temporary spiral, then cuts the temporary spiral out and replaces it with a sticky one. The whole structure goes up in under an hour, from an animal with a brain the size of a grain of rice. How do spiders make webs is partly a chemistry question and partly a geometry one.
Silk Is a Family of Materials
There is no single “spider silk.” A typical orb weaver produces at least seven types, each from a different gland, each with different properties:
| Silk type | Used for | Property |
|---|---|---|
| Dragline (major ampullate) | Safety line, web frame | Very strong, moderately stretchy |
| Minor ampullate | Temporary spiral, web reinforcement | Strong, low stretch |
| Flagelliform | Capture spiral core | Extremely stretchy |
| Aggregate glue | Droplets on capture spiral | Adhesive, absorbs water |
| Aciniform | Prey wrapping, egg sac | Soft, tough |
| Pyriform | Attachment discs | Cement-like |
| Tubuliform | Egg sac casing | Stiff, durable |
A single web uses at least four of them, combined in ways that would be difficult to improve on with synthetic materials.
Where Silk Comes From
Silk starts as a liquid protein solution — a dope — stored in glands in the abdomen. It is pulled through a tapering duct toward a spigot on a spinneret, and everything changes in that duct.
As the dope is drawn down, the proteins align into sheets of beta-sheet crystals linked by amorphous chains. The phase change is triggered by shear force and by pulling water out of the solution. The spider is not extruding hardened silk; she is drawing it, and the drawing is what makes it strong. A spider suspended on her dragline pulls silk out of herself by weight alone.
Building an Orb Web, Step by Step
The sequence is fixed, and it solves a real problem: how to build a large structure in three dimensions while standing on it. It also answers how do spiders make webs so consistently — each step depends on the one before it.
- The bridge — the spider releases a line into the wind until it catches, or walks across a gap trailing silk. This becomes the top cable.
- The frame — she drops two anchor lines and connects them, producing a Y. Everything else hangs from this.
- The radii — she walks out along the frame, paying out silk, and returns to the hub, repeating 20 to 30 times.
- The auxiliary spiral — a loose non-sticky spiral from center outward, holding the radii apart while she works.
- The capture spiral — working inward, she lays down stretchy, glue-covered silk, spacing each loop by feel, then cuts away the auxiliary spiral.
Total: about 20 to 60 minutes and, for a large orb, 10 to 20 meters of silk. She will often eat the old web and rebuild daily, recycling the protein.
Why She Does Not Stick to It
The capture spiral is covered in microscopic glue droplets, and they do stick to almost anything — including, in principle, the spider. She avoids them by walking only on the radii, which carry no glue, and by gripping with specialized claws and hairs rather than the flat of her tarsus.
Experiments have shown that the glue adheres poorly to the spider’s own cuticle. So the answer is partly anatomical, partly behavioral: right surface, right gait.
How Strong Is Silk, Really
By weight, dragline silk is stronger than steel and comparable to high-grade synthetic fibers in tensile strength. The more interesting number is toughness — the energy required to break it — where silk beats Kevlar by a wide margin because it stretches before failing.
That combination is why a web survives a bee hitting it at speed. The capture spiral absorbs the impact by stretching several times its length, and the energy dissipates instead of snapping the line.
Not All Webs Are Orbs
Orb webs get the attention, but they are a minority. Cobweb spiders build messy three-dimensional tangles in corners. Funnel weavers build a flat sheet with a retreat tube. Sheet weavers lay horizontal platforms with vertical knock-down threads. Bolas spiders swing a single sticky droplet on a line at moths. Trapdoor spiders skip the web entirely and ambush from a burrow with a hinged lid.
And many spiders do not build webs at all. Jumping spiders stalk prey and pounce; wolf spiders chase it down. Silk is universal among spiders — every one of them uses it for draglines or egg sacs — but the web is one application among many.
Keep Exploring
- What is pollination? — the other animal-built structure that keeps ecosystems running
- How do bees make honey? — another case of animals manufacturing a material
- Why do birds sing? — animal signals built for a specific receiver
