Silkworm Gut: The Fishing Line Made From the Silk Gland

Not Catgut. Actual Silkworm.

For centuries the finest fly-fishing leader available was "silkworm gut" — and despite the name it was neither catgut nor intestine. It was the silk gland itself.

The gland was removed from a larva that had finished feeding and was about to spin, then drawn out and dried into a single translucent strand. The animal was killed just before the moment it would have made silk, and the silk was taken in liquid form instead.

Why Anglers Wanted It

It was flexible, strong, and very nearly clear — the last of which mattered most. A leader is the section between line and fly, and a fish that sees it does not take the fly.

The envy is on record. In The Compleat Fisherman of 1724, James Saunders wrote admiringly of Swiss and northern Italian anglers who made "a fine and exceedingly strong hair or line, resembling a single hair", and judged that nothing else in nature of that size would match silkworm gut for strength.

An Industry Behind It

This was not a cottage practice. Most silkworm gut imported to the United States through British dealers came from worms raised in Murcia, Spain, with the glands extracted from pickled larvae immediately before they would have spun their cocoons.

An entire regional industry existed to produce fishing leader from an animal domesticated for cloth.

What Ended It

Nylon. A synthetic monofilament that is clear, strong, consistent, available in any length, and does not require killing a caterpillar at a precise developmental moment.

Silkworm gut survives now as a collector's item — hanks of it turn up in museum collections and in the hands of anglers who fish antique tackle deliberately.

The Pattern Again

Cloth, sutures, fishing leader, dissolving electronics. Every era finds a use for this protein and then finds a synthetic that does the job more conveniently — and then, often enough, comes back.

Related: silk in medicine · the history of sericulture