Moths and butterflies are closely related insects: their order, Lepidoptera means ‘scaly wings’.
Although moths evolved long before butterflies, both are thought to have co-evolved with plants. One key difference between them is that butterflies generally have thin antennae, sometimes with a small ball at the tip, whereas moth antennae are often feathery. Day-flying moths are often brightly-coloured or patterned, appearing distasteful to potential predators, whereas nocturnal moths have more subtle colours and patterns to help camouflage them at rest during the day.
Adult moths are important food sources for other animals, and pollinators for a wide variety of plants, although some never feed. Moth caterpillars are often spectacularly hairy and patterned, again to put off predators, and often feed on plants particular to their species. The Elephant Hawkmoth caterpillar even has Himalayan Balsam as one of its foodplants – a great benefit to conservation efforts!
Sadly, two-thirds of common and widespread macro-moths have declined in number over the last 40 years, which has a knock-on effect on the species that feed on them, such as bats and birds. The decline in cuckoo numbers may be directly related to a lower abundance of moth caterpillars. The decline in moth numbers is probably related to loss of healthy habitat, among other factors, and so restoration of our peatlands is providing more space for them to thrive.
Moths, being sensitive to change, are useful indicator species, and so monitoring their numbers on a regular basis can give us vital clues to the health of our sites. We use an actinic light-trap once a month to survey moth numbers. Moths are thought to use bright nocturnal lights (the moon, mostly) as a guide to navigation on the wing, by keeping a constant angle to it. With a brighter, closer light, the angle changes more quickly and the moths instinctively try to correct it, ending up circling around the light and eventually dropping into the dark box beneath.
For more information on the current status of Britain’s moths: State of Moths Report 2021.pdf (butterfly-conservation.org)