According to research by the wildlife charity Butterfly Conservation, moths are in crisis. The UK population has plummeted by 33 per cent since 1968 because of habitat loss, chemical and light pollution and climate change. This matters because moths and their caterpillars are vitally important as pollinators and a food source. The Royal Horticultural Society (RHS) and Wildlife Trusts’ annual Wild About Gardens campaign is focusing this year on the insects, to encourage the UK’s 41 million gardeners to help them. RHS Garden Wisley in Surrey is running a summer project called Bringing Nature Home – Garden Plants for Caterpillars, looking at which non-native plants we can all grow to help succour them.
The problem is that many gardeners still view caterpillars as an enemy, an attitude that is ill-informed and unwarranted, says Josie Stuart, a senior entomologist at the RHS. “Caterpillars are an important food source for animals including birds, frogs, wasps, ground beetles and bats,” she says.
According to Butterfly Conservation, in Britain and Ireland, blue tits alone eat an estimated 50 billion moth caterpillars a year. A baby blue tit needs to eat 100 caterpillars a day for the first three weeks of its life, says Kate Bradbury, an RHS ambassador. Other animals depend on them too, she adds: “Everyone thinks hedgehogs eat slugs and snails but they prefer caterpillars, beetles and earthworms.”
Caterpillars are a major food source for many animals, including blue tits – Neil Aldridge /iStock
Despite the crucial role caterpillars play in the food chain, the RHS gets a lot of calls from gardeners anxious about caterpillars eating their plants. Stuart says that in most cases they should be left alone to munch: “If a plant is well-established in your garden, a caterpillar nibbling at its leaves is not really going to do that much damage and it’ll be able to grow through that slight loss of leaf. A nibbling caterpillar is a sign that your garden is working.”
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This includes the ermine moth caterpillar. The prevalence this year of the thick, white webbing that it spins to protect itself from predators, which gardeners have noticed on their plants, has caused a flood of concerned enquiries to the RHS.
“Because the webbing is a bit Hallowe’en-y, it looks scarier than it is,” says Stuart. “The caterpillars don’t do much damage to the plants they’re on and the defoliation they cause is usually manageable, so the plant recovers.”
The caterpillars that are not your friend
There are two species that are more worrying. The codling moth caterpillar burrows into fruit, mainly apples and pears. The first protection is to encourage its natural predators into your garden, says Stuart. You can also hang pheromone traps in fruit trees in May which capture male moths to disrupt the female’s egg-laying cycle.
If you still have a problem, using a biological control of pathogenic nematodes can help, although the drawback is that they might kill other insects. The box tree caterpillar has wreaked devastation on the shrub (Buxus sempervirens). Vigilance helps: it’s best to pick off caterpillars as soon as they appear. It also has some natural enemies, including wasps, and there are biological controls. Stuart says that box is sturdy and can recover, but if a plant has been badly hit, a better idea might be to plant an alternative shrub. The RHS website has a list of options.
The box tree caterpillar is not your friend – Marina Denisenko/iStock
The underrated moth
Like caterpillars, moths have an image problem. Despite being taxonomically similar to butterflies and sharing the same order of lepidoptera, they are viewed as inferior dullards.
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This is unfair, say Stuart and Bradbury. With 2,500 species, moths are prolific pollinators night and day. While most pollinate evening bloomers such as tobacco plant (nicotiana), evening primrose, honeysuckle, jasmine, and white campion, there are 150 species that fly during the daytime. This far outweighs the UK’s 60 species of butterfly. Nor are moths all small, brown and boring. Many are impressively patterned and often mistaken for butterflies.
“We have some beautiful moths,” says Stuart. “The elephant hawk moth is one of my favourites, it’s bright pink and olive-yellow. It looks almost tropical and is fairly common across the UK, especially if you have fuchsias, which it likes. A really pretty day flier is the mint moth, it’s almost burgundy-purple with yellow flecks on its wings. Another brightly coloured one is the brimstone moth, which is a luminous yellow-green colour, super bright almost like a highlighter pen.”
The elephant hawk moth – Sandra Standbridge
Other fascinating species include the red and black cinnabar, the distinctly marked angel shades and the scarlet tiger.
Reassuringly, moths prefer plants to clothes, with just two of the species likely to feast on your wardrobe.
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“There’s so much focus on what we can do for bees and butterflies in our gardens but we need to remember that butterflies start their lives as eggs which turn into caterpillars, and so do moths,” says Bradbury. “I’d love people to care about caterpillars as much as they do about pollinators because they’re just as important.”
Caterpillars and moths need a wide variety of plants in your garden. Butterfly Conservation recommends starting with a “wild space” of five favourites with the insects: jasmine, bramble, marjoram, willow and nettle.
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