Some gardeners view the autumn as a time to tidy up the garden when the last flowers have finished blooming. From October onwards I see lots of people out cutting and chipping things, and even burning leaves which would be much better turned into leaf mould or used as a mulch on flower beds. But the worst aspect of this is that many of the butterflies and moths we love to see will be inadvertently killed as they overwinter on plants in our gardens. Some spend the winter as eggs stuck to the bark of trees and shrubs, and only hatch out the following spring when the plants begin growing again. Others might be caterpillars that stop feeding as the temperatures get lower, only resuming their feeding when winter is over. Some even spend the winter wrapped in the safety of a chrysalis or cocoon, waiting until spring or summer to emerge as a beautiful butterfly or moth.
When gardening in autumn and winter, I am always mindful that there are likely to be dozens of butterfly and moth species around me that I simply can’t see because they are spending the winter in one of these ways, and are almost always extremely well-camouflaged or hidden in fallen leaves. Here are my favourite butterflies and moths that need us to be a bit more relaxed in our approach to garden tidying.
Garden Tiger moths are some of the most spectacular moths to find. Their striking black stripes and spots give them their tiger name, but this is one of the species whose caterpillars are probably better known than the adults! Often called Woolly Bears, you can see the hairy caterpillars crawling around, often going across lawns or basking on warm paths in summer. The hairs on the caterpillars are used to deter potential predators like birds, but they are extremely vulnerable in autumn and winter as they spend that time tucked away among leaves on the ground. Caterpillars of this and many other species are easily killed if a gardener comes along and cuts everything away, removing all of the material to the compost heap or burning it. In my garden I let leaves lie where they fall on planted areas, and let all of the herbaceous plants die back naturally in winter. If leaves are on the lawn I gather them up to make leaf mould, or spread them on the flower beds to suppress the weeds.
Elephant Hawk Moths also spend the winter among leaf litter, but caterpillars of this species are fully grown in late summer and don’t feed in spring. So they spin themselves a cosy silken cocoon among plant debris, and won’t emerge from it until early summer of the following year. When they do emerge, they’re a beautiful big moth with pink and olive-green wings. These adult moths mate, and females lay their eggs on herbaceous plants with big leaves, like Willowherbs and Fuchsia. The caterpillars munch away on those for a few months, becoming extremely large – up to 8cm long – and chunky, with spots near their heads that look like eyes. These spots might fool predators into thinking they are a harmful animal such as a snake, so they don’t get attacked by birds. Gardeners often encounter them moving across the ground in late summer as they search for a place to make their cocoon, so help them out by leaving lots of plant debris and leaves for them that can remain there all winter.
Then there are the species that begin their life cycle just as everything else is winding down for the year. Moths such as the Canary-shouldered Thorn only start flying in late summer, and can be around until the middle of October. As well as being the cutest moth with a body covered in thick yellow hair (like a Canary), they’re very well camouflaged when they land on the yellowing leaves of the trees they lay their eggs on, including birch and alder.
As they emerge so late in the year their caterpillars wouldn’t have long to feed before the leaves fall and the food source dwindled. It’s safer for them to delay hatching until spring when the new leaves are on the twigs, and that’s just what they do! In nature this strategy works well, but it’s riskier in gardens if there’s a chance that trees will be pruned back in winter. So our advice is to reduce the cutting of hedges and trees, or to do it on a rotational basis where you leave some sections unpruned one year and prune them the following year so that you can maintain the shape of the hedge.
As well as being a joy to see, butterflies and moths are extremely important parts of garden food webs. Some of the birds that nest in gardens, such as Blue Tits, need a steady supply of fresh food – including caterpillars – to feed to the young birds in the nest. Each chick can eat 100 caterpillars per day, so the parent birds might need to find up to 1000 caterpillars per day to raise a large nest! Having more space for butterflies, moths and other insects can help encourage a huge range of other animals in the garden, and being mindful of them even when we can’t see them is one way to help boost their numbers.