Moths are vital to our ecosytem. They are important pollinators of flowers, but also an essential part of the food chain for many other species such as birds, bats, hedgehogs, shrews, frogs, toads, lizards, spiders and other insects. For example a brood of blue tits require around 15,000 caterpillars, equating to 35 billion caterpillars per year. Moths form a large part of the diet of bats and other garden birds such as robins, great tits, wrens and blackbirds which rely heavily on caterpillars.
Are moths declining rapidly?
The UK has around 2,500 different moth species, however numbers have decreased by a third since 1968 and 62 species have gone extinct. Others, like the Reddish Buff and Barberry Carpet are highly threatened whilst others such as the Bordered Gothic and Brighton Wainscot may already be extinct despite intensive searches in former locations. The UK Government has identified more highly threatened moths than birds or butterflies.
In some instances species decline has been even more dramatic with the once abundant and beautiful Garden Tiger Moth down by 89%. The brown furry caterpillars of the Garden Tiger are known as ‘Woolly Bears’ and were commonly seen wandering across open ground looking for somewhere to pupate. It is thought that the Garden Tiger caterpillars have adapted to survive long frosty winters and they now don’t do well in mild wet winters and the warmer springs of recent years.
What’s threatening moths?
The cause of decline seems to be multi-fold with agricultural intensification and commercial forestry, urban development and climate change playing a factor.
Intensive agricultural practices involve the use of monoculture, pesticides and herbicides to achieve higher yields. Pesticides will kill the moth or caterpillar directly, whilst the use of herbicides eradicates moth-friendly plants such as grasses, thistles and knapweeds. The use of monoculture does not provide the necessary vegetative variety to support a diverse species of moths and moth caterpillars.
Loss of green spaces and intensive urban and industrial development means the loss of habitat to support moth species. Light pollution can also be a problem, with the flying time of night-flying species reduced by artificially induced daylight conditions. Urban gardens can also be sterile environments for moths with gravel, decking and concrete and again light pollution leaving no space for moths.
Survival in the urban environment can be a challenge but the ‘Peppered Moth’ has been recorded as evolving a dark colour pigmentation in order that they would blend into the blackened polluted background of industrial areas. This process of industrial ‘Melanism’ was described by Kettlewell and meant that the adapted ‘Peppered Moths’ were harder to spot by predators.
With climate change the southern and northern ranges of different species are changing. With milder conditions some species such as the Cinnabar Moth are now spreading north into Scotland to find the cooler conditions they require. However, this assumes that there will be suitable food plants available to support them. Moth life-cycles have evolved to be synchronised with their food-plants, but climate change may alter the timing of the emergence of leaves and flowers of plants and trees. This then has a knock-on effect if the timing of the emergence of caterpillars does not coincide precisely with the bird breeding cycle and feeding of the chicks.
The surprising talents of moths
Many moths are absolutely stunning to look at, even more beautiful than some butterflies. Many moths are brightly coloured to indicate to predators that they are bitter to the taste and not good to eat!
Others are less striking for good reason, so that they are camouflaged and don’t get eaten. The majority of moths are night-flying species, but there are also over 100 species of day-flying moths, that’s more than the number of butterfly species in the UK!
Some moths employ deception such as the Death’s-head-Hawk-moth which makes squeaking noises to sound like a Queen Bee, allowing it to sneak into bee hives unchallenged and steal honey. The Bee Hawk-Moth has evolved to look like a bee so that predators think it has a sting and avoid it.
Moths can both smell and hear. Some moth species pick up the echolocation calls of bats and take evasive action. Others make their own squeaks to confuse the bats. Male moths use their antennae to smell the pheromones emitted by females to attract males.
Nearly all British moth species are harmless. There a just a few which give the others a bad name.
There are a couple of species of Clothes Moth that will chew holes in woolen jumpers, fur or feathers. They only attack fibres of natural origin, so clothes made of synthetic fibres are safe. The Clothes Moth prefers dirty clothes that are stored in a dark and undisturbed place. So the use of cedar balls and the regular cleaning and storing of vulnerable fabrics in sealed polythene bags should avoid problems.
There are a couple of moths whose caterpillars can cause unsightly damage in the garden or hedgerow. The Horse Chestnut Leaf Miner moth causes chestnut leaves to go brown and the Oak Processionary can defoliate Oak Trees. This species and also the Brown Tail should not be handled as their long hairs are irritant to humans.