Friday, December 2, 2022
Home SCIENCE Slug numbers appear to decline after UK heatwave | invertebrates

Slug numbers appear to decline after UK heatwave | invertebrates

As dew-covered sunrises make their way into UK orchards and pumpkin patches, gardeners across the country are noticing the absence of at least one slippery pest. The number of slugs appears to have been reduced as a result of the ongoing drought.

“I went to survey a wooded site last week and it took me over 30 minutes to locate a slug. Typically, you would expect to find them under almost every log in that habitat,” said Jake Stone, a zoologist at the University of Cambridge. “I thought there would be less, but I have never seen such a low number. But I guess that’s to be expected, because it’s rarely been this hot and dry.”

Paul Hetherington of Buglife, an organization dedicated to invertebrate conservation, said: “We’re actually quite concerned about most invertebrates. The slugs and snails will have suffered greatly. When it is very hot, slugs burrow into the ground and snails hibernate, similar to how they do during winter. But it’s likely that this prolonged heat and cooking of the soil killed many of them.”

Although slugs feature high on the list of “most annoying garden pests”, only nine of the 44 recognized species in the UK actually eat garden plants. “Most are very beneficial in the garden because they break down dead plant matter and recompost it,” Hetherington said. “There’s also the ripple effect in things that eat slugs and snails: thrushes, amphibians, hedgehogs – all of these creatures are in decline right now.”

This year has seen one of the hottest and driest summers on record, with most of England still officially in drought, despite recent rain. That’s bad news for slugs and snails, because their bodies dry out quickly if they’re active without moisture to sustain them.

“To avoid this, they are usually only active when water is freely available,” said Dr Gordon Port, an expert on slug behavior at Newcastle University. “When it’s not, they kind of go into a silent mode and wait for conditions to improve.”

He agrees that slug activity may be lower than normal due to dry weather, but he’s not necessarily worried about that. “I think it’s inevitable that more slugs have been killed than usual, because some will have been trapped in positions where they couldn’t take shelter,” he said. “The slug eggs can’t move either, so some of them may have dried up and died. But I think any enthusiasm for his demise may be premature. They have a remarkable habit of recovering.”

In previous research, Port and his colleagues collected every slug they could find in a defined area of ​​soil for two weeks and then let them recover for the next two weeks, a process they repeated for several years. The area was also secured to ensure no more slugs could enter. “Even after 18 months, slugs kept showing up,” Port said. “A lot of them had been sitting on the ground and just weren’t active, or hadn’t been caught when we were looking for them. They have a remarkable ability to survive.”

Slugs and snails also have another card in their favor: “They have done very well in recent years because we have had much warmer and wetter winters. Instead of hibernating, they have been eating and reproducing, which means their numbers were quite high before this happened,” said Hetherington. “Hopefully this spell won’t be too detrimental to their eventual number, but for a lot of other bugs, it’s very, very concerning.”

Dr Hayley Jones, Senior Entomologist at the Royal Horticultural Society, said: “We were looking for slugs in July and August as part of an RHS summer fellowship project and found it difficult to find them during this period. They reappeared in late August once the rain came, as slugs are generally very hardy. However, we would expect the prolonged drought to mean that fewer individuals survived the summer, so numbers will be reduced.

“Slugs and snails are great at reproducing, so they should bounce back next year, but if these kinds of extreme weather events become more common, populations could be affected in a more noticeable way.”


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