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Cocoon: Noun; A silky case spun by the larvae of many insects for protection as pupae (Oxford Dictionary).
The cocoons in my photos are those of Burnet moths, both 5-spot (below left) and 6-spot (below right): you can’t tell the difference in the cocoons from the outside – I just know which moths were present in the locations where I took my photos.

After hatching from their eggs, the caterpillars/larvae of both moths feed on plants from the pea family; the 6-spot burnet is particularly partial to Common bird’s-foot trefoil, which is why I see a lot of these moths at Cosmeston.

When they’re ready to pupate, the caterpillars find themselves a suitable location, often high up on a sturdy grass stem (though I have seen them on other plants), and spin an oval-shaped cocoon. The cocoons pictured above are still occupied by caterpillars in the throes of metamorphosing into moths, a process which takes about two weeks.

These are the empty cocoons that remain once the adult moths have emerged (with the remains of the larvae’s pupae cases poking out the tops). The cocoons are quite sturdy: their yellowish-white papery structures often seem to last for a month or more after the adults have departed or even until the grasses themselves collapse with the coming of the wild winds and chilly days of autumn.