Biodiversity: glowworms are disappearing

It is normally at this time of the year, in June-July, that they are sometimes seen at night in the gardens. Unfortunately, glowworms are becoming rarer. A British study sheds light on the causes of this disappearance.

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A glow worm on a leaf in a garden.  (MOURAD ALLILI / MAXPPP)

There are about ten species of glowworms in Europe, but for 60 years these luminous points have been lighting up less and less in gardens or meadows. In question: the use of anti-slugs and clearing. But also the nocturnal lighting that harms romantic encounters. In the glowworm, in fact, the females do not have wings but they glow (bioluminescence is a chemical reaction which gives them a fluorescent green abdomen), and this is how they are noticed by their male partners, who have wings and can fly in their direction.

The problem is that the light from street lamps complicates this seduction. A team of biologists from the University of Sussex has just confirmed this through laboratory experiments. They simply placed decoys that mimic the glow of a female glowworm in a maze and timed how long it took a male glowworm to spot them. In the dark, everything is fine, 100% of encounters take place. But when these researchers illuminate the device with a more or less strong white light imitating that of street lamps, then only between 20% to 70% of males manage to locate their partners and it takes on average twice as long. This observation is not brilliant: it is disastrous for the reproduction of these insects, which are both fascinating and very useful in a garden. Glowworms help eliminate slugs naturally.

Artificial lighting disrupts the biological rhythm of many species

Unfortunately, glowworms are not the only ones to suffer from light pollution. Light is indeed one of the main causes of extinction of insects (after pesticides): by turning around lampposts at night, they become easy prey for bats and birds. A real-life study in Great Britain has shown that areas lit at night have half as many caterpillars and moths as those far from light.

Moreover, beyond insects, artificial lighting disturbs the biological rhythm of many animals and also ours, to us humans. The Academy of Medicine has even recommended in a report to include night light in the list of endocrine disruptors.

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