Spider silk beats steel, but we're stumped

If you scaled a spider's dragline silk up to the thickness of a pencil, it could stop a Boeing 747 in flight.

That is not a metaphor. It is the math. Dragline silk has a tensile strength comparable to high-grade steel and a toughness — the energy it can absorb before breaking — that exceeds Kevlar. It is biodegradable. It is produced at room temperature, in water, from a paste of protein. Our best industrial fibres require furnaces, solvents, and a lot of regret.

A spider makes it inside a gland about the size of a sesame seed. Liquid silk protein enters one end as a sort of structured goo. As it travels through a narrowing duct, water is pulled out, salts are swapped, the pH drops, and the molecules align under shear stress. By the time it exits the spinneret, the protein has assembled itself into one of the strongest materials biology has ever evolved.

Try to reproduce this in a lab and the protein clumps into useless lumps within seconds.

We have known the rough chemistry for decades. We have sequenced the genes. We have inserted those genes into goats, whose milk now contains silk protein, and into bacteria, and into silkworms. The proteins come out fine. The fibres do not. Whatever the spider's spinneret is doing in the last millimetre of its duct, we cannot copy it. The geometry is too precise.

A garden spider builds a fresh web every night and eats the old one to recycle the protein. The web you walked through this morning was a single-use, fully biodegradable, self-assembled fishing net stronger than anything humans manufacture.

There are spiders in Madagascar whose silk is gold. Bridge-building spiders that fire threads across rivers using updrafts. Diving bell spiders that spin silk underwater. Spiders whose silk hardens further when wet.

We invented Kevlar in 1965. Spiders have been refining theirs for around 380 million years.

The lead is not closing.