Council changed street lights because old lamps were interfering with glow worms having sex

Council bosses in Wales turned off traditional street lights because they were interfering with glow worms’ mating habits. The sodium illuminations were tempting away the male insects, which meant they were failing to copulate with the females. But since the lamps have been changed to LED ones, the males are no longer being lured away to the lights, and the population around Llandudno’s Great Orme has boomed.



The realisation that the sodium lamps were interrupting the mating patterns was made by amateur naturalist Jenni Cox, who noticed the problem on Marine Drive. She said: “I first discovered them in 2011 when I was just walking down Marine Drive. I reported my findings to the national glow worm survey and came back out to count them. I counted 300 females, although there didn’t seem to be many males finding them. Then eventually I noticed up to 50 males were congregating under the street lights and I wondered whether that was stopping them finding the females, so I reported it to the council’s biodiversity officer, Anne Butler.”

Many experts believe numbers of glow worms (lampyris noctiluca) are on the decline due to pesticides, loss of habitat and light pollution. Yet Jenni’s painstaking study, in which she counted males and females on the Orme every night through the mating season, is helping inform the bigger picture about their numbers and habits. She has counted as many as 700 females in a single night, 800 including males. Glow worm larvae live for around two years, which is the only time they feed. They eat insects, slugs and snails, injecting them with poison which decomposes the prey, then suck up the resulting broth, which helps to maintain the eco-system.



The light emitted by the females (bioluminescence) is caused by a chemical reaction within its tail. Females lay between 25-100 eggs and die soon after. Jenni added: “I just hope all this work I have put in does help glow worms on a bigger scale in the future. I’m happy that I have helped these here but if it helps on a bigger scale I would be really happy.” The council's Anne Butler said: "Jenni brought it to everyone's attention a few years ago. We did a few trials with different street lights and we had really good co-operation from the street lighting team."