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Fall 2012

Urban Jungle

The changing natural world at our doorsteps | Illustration and text by Patterson Clark      

November 20, 2012

Burdock: Sowing seeds with fur and bur

Bounding home from an adventure in the weeds, a dog can carry home burdock burs, spiny, seed-filled fruits that hook into its fur.

Native to Europe and a common invasive weed in the United States, burdock yields burs that can be very difficult to extract from a pet's coat. A bur can be so tenacious that groomers are advised to massage oil into the spot before combing it out. Often, scissors are necessary.

In the 1940s, Swiss agricultural engineer George de Mestral was curious about the burs on his hunting dog. The bur's design inspired Mestral to invent the hook-and-loop fastener that most people now know by the brand name Velcro.

The key to the grip: Tiny hooks at the end of numerous flexible spines. Velcro latches onto nylon loops. Burdock burs grab onto fur, sweaters, hair and feathers.

Small birds can sometimes be entangled by clusters of burdock fruits, which can trap them like flypaper. As a bird struggles against the burs, more and more hooks grab onto feathers. Sometimes a bird is completely immobilized and if not rescued will soon die of starvation.

It's a rare sight, but goldfinches, kinglets, warblers, hummingbirds, wrens, chickadees — even small bats — are sometimes found dead, plastered to the head of a burdock fruit stalk.

But if a big bird or large mammal brushes against the plant, the burs will tear away from the stalk and hitch a ride, employing the hapless animal as the plant's dispersal agent for sprinkling seeds that will sprout into many more opportunities for groomer — and animal — misery.

Sources: Michigan State University Extension, Wilson Bulletin, Velcro

Burdock, arctium

Bur cut open to reveal seeds