If you feel like you’ve seen more bugs this summer – moths in the bedroom, flies in the kitchen, spiders, well everywhere – you’re not alone. Many people across the UK are reporting seeing more insects, especially ladybirds, wasps and butterflies, in the warmer months.
This year has been the hottest and sunniest spring on record across the UK, and with multiple heatwaves causing soaring temperatures in the mid thirties, certain types of insects are thriving. “What we’re seeing generally across the board is that there are more insects,” says James Logan, professor at the London School of Hygiene and Tropical medicine. “That’s as a result of climate change, and the summer becoming warmer with shorter, warmer winters as well.
“Temperature is one of the biggest things that affects any insect and we tend to see that they do better in warmer weather. What we’re seeing right now is a transition phase where temperatures [warming] is nicer for them to thrive.”
It’s not just the weather though, he adds. The urbanisation of the country, changes in agriculture and sea levels rising will all shift the bug ecosystems in the UK. “We’re seeing now is gradual shifts where some insects are doing really well. Those effects are starting to happen but it’s going to be in the next 10 to 20 years that we’re really going to see the impact.”
We asked the experts what insects are thriving, and what we should expect to see more of.
Butterflies
Butterflies are one of the only insects that we have long-term data sets for in the UK, and they have been in general decline since the 1970s but this year is a different story. “We’re seeing large movements of white butterflies, coming in off the sea and moving into the country,” says Gavin Broad, the Principal Curator at the British History Museum.
“Caterpillars are dependent on the external temperature for their metabolism. If it’s cold and wet they can’t move as quickly, eat as quickly, and are slowed down. For the adults, they can’t disperse as much. An insect requires warmth to be active. They can fly around and colonise different areas.”
The heat is important for their flight, adds Logan. “Sometimes you see butterflies resting on a surface with their wings spread, and you see them slowly moving their wings up and down. Often what they’re doing is trying to get the energy from the sun and heat up their bodies to move.” Flying around will also help them locate food sources.
Mosquitoes
“As the weather gets warmer, we’re going to start seeing many more invasive species coming to the UK such as mosquitoes that bite us. We’re going to start seeing diseases being transmitted here that weren’t before,” says Logan, who co-founded Archtech Innovation, a company harnessing insect intelligence to detect threats.
Other countries experience huge problems from mosquitoes transmitting malaria or dengue fever. Similar issues could arise here. “There’s a very high risk of the introduction of the Asian tiger mosquito, or Aedes albopictus mosquito, which is established throughout Europe and has been found here in the UK on a number of occasions. We don’t think its breeding here and it’s not established here yet but, without a doubt, it’s a case of when it will be established, not if.”
This mosquito can transmit dengue fever, which is already happening in France, Belgium, Spain and Portugal. “It’s only a matter of time before we start to see the same thing here”.
Dr Luke Tilley, a British entomologist and Director of Communications and Engagement at the Royal Entomological Society, says it won’t be immediate. “Mosquitoes are vectors which is what we call insects that carry disease. It doesn’t mean we’re going to get dengue fever because it needs to have been carried from a person with it to another. It does mean that the likelihood increases. We’re keeping a close eye on the vectors.”
He mentions a well-known example in the “underground-adapted mosquito found in the London Underground”. “It cannot survive above ground, showing how insects can specialise in response to very specific environmental conditions.”
Wasps
There are around 9,000 species of wasps in the UK, and they can be split into social wasps (that live in communities, usually a single nest that houses dozens or thousands) or solitary (where the females acts alone).
Social wasps have had a good year. And, although they can be pests in the home, Broad thinks it’s good news for us. “Wasps form a very useful function as they keep other insect populations in check. Without them, there would be a biomass of insects around. They’re consuming a lot of caterpillars and aphids right now so that’s pretty useful.”
Luckily for those worried about wasps, an abundance of them is well off. “They build nests discreetly and space themselves out so there’s not going to be a really high density. Because of the changing climate here, we won’t get into a situation where we have a plague of wasps. It also doesn’t take much to wipe them out. Each nest will be full of other things eating the wasp larvae as well.”
Bees
Bees are similar to wasps. “They hibernate over the winter so queen bees probably have a better chance of surviving if winters that are a little bit warmer. They’ll potentially have more generations in one year,” says Logan. “They could hibernate for fewer months of the year and their activity will come about earlier.” To put it succinctly, more bees will survive the winter.
With people letting their gardens grow, and the increase in wildflowers, pollinators like bees and wasps, will be encouraged. It’s worth noting, he says, that bees, wasps and hoverflies look similar and often get mistaken for each other.
But there are issues for bees here. The Varroa mite is an invasive species that impacts beehives and kills them, and agricultural insecticides can harm them too.
Moths
Similar to other insects, warmer summers will mean moths won’t need to hibernate for as long and have longer breeding seasons. But an important thing is the urbanisation and light pollution building up here, as they’ll be attracted to the light of new houses and buildings.
“One type of moth that’s a big problem is clothes moths,” says Logan. “As they breed quicker they can be a nightmare to get rid of and they eat clothes.”
Flies
Logan spent last week dealing with a lot of flies in his home, and this could become more common for us in the UK with warmer temperatures as they have longer to breed. “A longer breeding season means they can breed faster and survive better in winter months.
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“We’ll probably see them hatching earlier as well so as spring comes, that spring might be earlier and they can reproduce quicker within the year. Instead of having two generations, they might be able to have three or four.”
The heat also causes food to rot quicker, which attracts flies into the home. Leaving windows and doors open, and this food available to them and not covered up, will invite them into houses.
The key is to discourage them in the first place. Logan cleans his dogs feeding bowl after each meal to avoid the smell of residue meat. He recommends not leaving washing up to get dirty, not leave food around, and putting screens on windows and doors.
Ladybirds
There is a lot of anecdotal evidence for an increase in ladybirds, which comes hand in hand with an increase in aphids (or green flies). “Ladybirds eat aphids, so when aphid numbers boom, often in warm, wet springs, predators like ladybirds can quickly follow. These dynamics are closely linked,” says Tilley.
Ladybirds are often regarded as a positive as they eat aphids, that take the sap and sugars from a plant, but there are negatives in the Harlequin ladybird. “When they increase in numbers, they start to become a nuisance.” They’re one of the most invasive ladybirds globally and outcompetes other native species for food. It can also enter homes during autumn to seek shelter for winter.
Worms and snails
It’s a different story for worms and snails, who would thrive from a “typical” British summer. “They need to be quite moist themselves, they’ll dry out if they don’t have a film of moisture around them. Snails can plug themselves into the shell, they can spend summer in there but slugs don’t have that option,” says Broad.
Is it a positive for us?
More insects in the house, or bothering your picnic, probably doesn’t feel like a positive for most people – but is it from a scientific point of view?
Logan doesn’t think so. “We risk losing some of our native species that are here because of the temperature that we’ve had for a long time. When that changes, we’re going to start losing some and they could become extinct. What we’re beginning to see is that it’s more conducive to insect species that shouldn’t be here and a lot of those can be problematic, like the mosquitoes that transmit disease. Overall I think it’s not necessarily a good thing.”
Tilley says it all hangs in the balance. “We will have to change, and how we change is a much wider issue than what the insects are doing. There might be changes in what we eat and grow in this country according to what pests are coming for our traditional crops, so it will give us lots of things to research so we can respond accordingly.”
There is one positive to the UK’s position. “I think the UK is well placed to be one of the best at looking at long-term monitoring. On this relatively small little island we’ve been documenting the natural world for longer than most countries so I think as long as we keep the public aware and then we get funding into the right areas then we could be well placed.”