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Country diary: a gorse seed weevil has a surprise in store

Phil Gates
·2-min read

“When gorse is out of flower, kissing’s out of favour” goes the old saying, currently out of kilter with pandemic social distancing rules.

Today, on a bleak, wintry morning, gorse bushes were coming into bloom all along this moorland road. Will these out-of-season bloomers, with no bumblebees to pollinate them, produce any seeds? Maybe, if buffeting winter winds dislodge pollen inside the flowers and they self-pollinate. And if they do, those seeds might escape their greatest enemy, the gorse seed weevil, Exapion ulicis, which hibernates in winter. This tiny beetle can be so destructive in summer that it has been used as a biological control agent to limit their host’s invasion of California and New Zealand, where it has become a noxious weed.

The adult weevils reappear in spring, feed on new growth of gorse and then lay eggs in flower buds. Their larvae eat seeds in developing pods, pupate, hatch into adults and await an explosive introduction to the outside world. When the sun dries gorse seed pods, tensions develop inside their walls until they split along their suture, fly apart and hurl out their contents. Popping pods and the pitter-patter of seeds and weevils hitting the undergrowth are characteristic sounds in a gorse thicket on a hot summer afternoon.

But some of these insects never escape to experience the outside world. Wet weather in autumn leads to leathery, soggy pods that don’t dry out and burst, so becoming a sarcophagus for imprisoned weevils. There were plenty of summer’s old unexploded seed pods among today’s fresh crop of winter flowers, so I brought some home. Most contained seeds, but when I cut one open a small black and green ball, about the size of a pinhead, rolled out from among mouldy seed remains.

For a minute it lay there, apparently dead, then suddenly six legs extended and waved frantically in the air, rocking the insect from side to side until it succeeded in righting itself. This predator-avoidance behaviour, thanatosis, feigning death when danger threatens, is a weevil speciality.

It paused to clean its antennae with its front legs, then scuttled off across the kitchen table, most likely looking for somewhere to hibernate.