Slug numbers appear to shrivel after UK heatwave

As dewy dawns break across the UK’s pumpkin patches and allotments, gardeners across the land are waking up to the absence of at least one slippery pest. Slug numbers appear to have shrivelled as a result of the ongoing drought.

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

Paul Hetherington of Buglife, an organisation devoted to the conservation of invertebrates, said: “We are actually quite concerned about most invertebrates. Slugs and snails will have suffered greatly. When it’s really hot, slugs go deep down into the ground, and snails go into hibernation, similar to the way they do over winter. But this prolonged heat and baking of the ground is likely to have killed an awful lot of them.”

Although slugs feature high on the list of “most annoying garden pests”, only nine of the 44 recognised species in the UK actually eat garden plants. “The majority are very beneficial in the garden because they break down dead plant matter and turn it back into compost,” said Hetherington. “There’s also the knock-on effect on things that eat slugs and snails: song thrushes, amphibians, hedgehogs – all of these creatures are in decline at the moment.”

This year has had one of the hottest, driest summers on record, with most of England still officially in drought, despite recent showers. That is bad news for slugs and snails, because their bodies dry out quickly if they are active without moisture to support them.

“To get around this, they are usually only active when water is freely available,” said Dr Gordon Port, an expert in slug behaviour at the University of Newcastle. “When it’s not, they go into a sort of quiet mode, and wait for conditions to get better.”

He agrees that slug activity may be lower than normal because of the dry weather, but he is not necessarily worried about it. “I think it is inevitable that more slugs than usual will have been killed, because some will have been caught in positions where they couldn’t get shelter,” he said. “Slug eggs also aren’t able to move, so some of them may have got dried out and died. But I think any excitement about their demise may be premature. They do have a remarkable habit of bouncing back.”

In previous research, Port and his colleagues collected every slug they could find in a defined patch of ground over two weeks, then left it to recover for the following two weeks – a process they repeated for several years. The area was also secured to ensure that no additional slugs could slime their way in. “Even after 18 months, we were still getting slugs turning up,” said Port. “A lot of them had been sitting down in the soil and just not being active, or not being captured when we were out looking for them. They do have a remarkable ability to survive.”

Slugs and snails also have another card stacked in their favour: “They have done very well in recent years because we’ve had much warmer, wetter winters. Instead of hibernating, they’ve been going about eating and breeding, meaning their numbers were quite high before this happened,” said Hetherington. “Hopefully, this spell is not going to be too detrimental to their eventual numbers – 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 searching for slugs in July and August as part of a RHS summer studentship project and found them hard to find over this period. They reappeared in late August once the rain came, as slugs are generally very resilient. However, we would expect that the protracted drought means fewer individuals survived the summer, so numbers will be reduced.

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

• Invertebrates

• Animals
• Drought
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