Clothes moths are not to be underestimated; they are incredible survivalists. Understanding their unique biology is key to gaining control of any clothes moth outbreak.
Destructive, secretive and difficult to control, clothes moths are occasional invaders with excellent survival capabilities. Though they cause headaches for homeowners by attacking items in the wardrobe, these moths are unique creatures with fascinating biology. Although there are two types of clothes moth – the webbing clothes moth (Tineola bisselliella) and the case-making clothes moth (Tinea pellionella) – here we have a close look at the webbing clothes moth, its behaviour and how this impacts its management.
A long history
Moths are ancient. They originated before butterflies, diverging from their ancestors about 300 million years ago, while butterflies appeared much later, about 98 million years ago. Clothes moths belong to Tineidae, the fungus moth family, pre-dating other, more recognisable species such atlas moths or silk moths.
Webbing clothes moths (Tineola bisselliella) are believed to have originated in Africa and expanded their range by hitchhiking on 19th century sailing ships. Today, they are truly a global pest and much like pest rodents and German cockroaches they can be considered peridomestic pests – humans have created such ideal environments for clothes moths inside buildings, they are rarely found outdoors any more. Although they are not generally regarded as a highly destructive pest, they are nonetheless an economically important species due to their ability to destroy a wide range of items. Indeed the damage they cause in the US alone has been estimated at nearly $1 billion.
Life stages
A webbing clothes moth begins its life as an egg about 0.3 mm wide – tiny, but still visible to the human eye. From there, it hatches into a cream-coloured caterpillar, the life stage that does all the damage. It spins silk as it eats to create its characteristic protective webbing. While customers with a clothes moth problem might assume clothes and fabrics are the target, they are actually after an animal protein – keratin. Keratin is a tough protein that hair, skin, horns and wool are all made from. Wool is a common food source for clothes moths, making woolly hats, jumpers, scarves and rugs all potential targets for hungry moth larvae.
Digesting and metabolizing keratin is hard work; it’s not entirely clear how these larvae achieve it. It is believed that a microbe in the gut produces a digestive enzyme to break down the protein, but research into this area is ongoing. Clothes moths are unlikely to eat cotton or synthetic fabrics, so damage to these items is probably from another pest, maybe silverfish.
Incredible survivalists
Webbing clothes moths are a remarkably robust pest. The eggs and larvae can withstand sub-zero conditions and temperatures up to 35°C. What’s most impressive is that they can metabolize their own water as a byproduct of keratin digestion. This mean they don’t need water – they can survive conditions of low humidity. That said, humans have created ideal environments for clothes moths; our homes maintain a fairly consistent temperature and humidity, there are very few predators, and we pack our darkest spaces with all kinds of delicious keratin-laden items.
Webbing clothes moths can remain as instars for between two months to two years, depending on conditions, and pass through 4-45 instars. When they are ready to pupate, the larvae will construct cocoons out of silk and bits of whatever they’re feeding on, making them difficult to spot. Once the larvae emerge from their silky cocoons as adults, the moths are easier to spot, but they are still secretive. They avoid the light and are poor flyers, generally preferring to scurry around, which means pest managers need to move and shake out clothes to spot their presence.
Adult clothes moths don’t eat, in fact they don’t even have functional mouthparts. They only live for a few weeks with the sole purpose of finding a mate. With no need for food or water, moths will live quite happily as adults for their short lives. They are attracted to the smell of woollens, and once established, send pheromonal signals to nearby moths to invite them to join them. Pheromone sticky traps can be used as a monitoring tool and are a useful element of any management program.
Clothes moth control options
For pest managers, managing a clothes moth infestation is challenging. Clearly, it’s not possible to remove all potential food sources, without a significant wardrobe re-fit, so complete elimination and ongoing management is required. Inspection is the key, to locate all areas of infestation. Infested items need to be thrown out or treated to eliminate eggs and larvae. This can be achieved by washing in hot water, placing in the freezer for two weeks or placing items in a bag in the hot sun for a couple of hours (to achieve a temperature of over 50°C). Wardrobes and drawers can be treated with a suitable residual spray and pheromone sticky traps can be used to pick up any stray adults and for ongoing monitoring.
Read more about clothes moths.
Reworked extracts from: In Defense of Clothes Moths, Marvels of Evolution by Isabel Novick. Entomology Today, March 21, 2023.
