Watch Out For The Marching Caterpillars!
Look carefully at the angle between the curb and the road
I knew nothing about marching caterpillars before moving to Switzerland. I first learnt about them when a friend developed a skin rash after some caterpillars dropped into his t-shirt as he was sitting under a tree!
What do marching caterpillars look like?
They are usually somewhere between three and four centimetres long, and they’re covered with thousands and thousands of pointed hairs.
There are two types: pine and oak. The pine marching caterpillars have a darker body. You can clearly see the hairs sticking out from the body and there is a rusty colour running along the back. The oak marching caterpillars also have a darker body but have a slightly yellower colour running along their back.
They’re called “marching caterpillars” because they literally move along in single file behind each other – in a procession. In fact, they’re also called processionary caterpillars, so you might have heard that term as well. In French, they’re called chenilles processionnaires.
Caterpillars on the move
The caterpillar life cycle
Pine and oak processionary moths lay their eggs during the summer months on twigs and small branches in the tree canopy. The eggs stay there over winter – they have a protective layer to shield them from the cold weather. The larvae start to hatch from the eggs in the spring – the larvae are the caterpillars.
During the spring and summer, the caterpillars are highly active. They live in the pine and oak trees and form colonies. You can see their large nests in the trees that look a bit like cobwebs or candyfloss.
When they’ve run out of the food from one tree, the caterpillars come down from that tree in a long, single file, following each other head-to-tail. They’re on the move to find another tree in which to set up camp so that they can pupate and undergo metamorphosis into their adult form, the moth. You can often see the caterpillars marching along in their single file procession, and they can cover large distances along the ground.
The caterpillars mature and develop over a period of about 9 to 12 weeks. They pupate inside their nests during the end of June/beginning of July, and the adult moths emerge one to two weeks later. They then lay their eggs and the life cycle is completed.
So what problem can the caterpillars cause for humans?
The problem is that they are covered in hairs and the hairs contain a toxin that is highly irritating to humans. The hairs can break off from the caterpillars very easily and can even become airborne – carried on the wind.
If skin comes into contact with the hairs, this can lead to an irritating, itchy rash. It’s like small, red, slightly swollen bumps on the skin. The rash might only last for a few hours but sometimes it can become scaly and eczema-like and last for a few weeks.
The airborne hairs may also be inhaled, and this can lead to wheezing and difficulty breathing, particularly in people who already suffer from asthma. And the hairs can irritate the eyes causing conjunctivitis – irritation, itchiness and redness of the eyes. Rarely, a severe allergic reaction (an anaphylactic reaction) may be triggered in some people who have come into contact with the caterpillar hairs.
The degree of symptoms experienced varies from person to person. Not everyone who comes into contact with the caterpillar hairs will develop symptoms. Some people don’t have any problems at all because they don’t react to the hairs.
What should you do if you see the caterpillars?
If you come across the caterpillars, the important thing is to stay away from them as much as possible – certainly don’t handle them in any way. And avoid any trees where you can see the nests.
Keep children and pets away as well. Explain about the caterpillars to your children. Teach them to stay away if they see them – especially if they love picking up creepy crawlies when they’re out exploring! Find a picture on the Internet so that they know what to look out for.
If you’re worried that there is a colony in one of the trees in your garden, then you should contact your community to get the nest removed. DO NOT try to get rid of the nest yourself. Even when the nests are empty, they can still contain large amounts of the caterpillar hair and that’s the toxic stuff. If you try to knock down or disturb a nest, then this can make the hairs airborne and easy to inhale.
What happens if it’s too late?
If skin does come into contact with the caterpillars or their hairs, then you need to remove them as quickly as possible. Put on a pair of gloves if available, to protect the skin of your hands whilst you’re doing this. Then wash the affected area of skin, followed by your hands, with copious amounts of soap and water.
Any rash can be treated with antihistamines – either in cream or tablet form – discuss the rash with a local pharmacist, or of course, see your doctor if you’re worried.
What to do if you think you have inhaled some of the hairs and you develop breathing difficulties? Anyone who has asthma should always carry their reliever inhaler when they’re out and about. The inhaler contains a drug that opens up the airways and so helps to relieve their wheezing and breathing problems.
So, if you have an inhaler already, take it. If you don’t already have an inhaler prescribed, then it depends on how severe your symptoms are. Obviously, anyone with very severe symptoms should see a doctor and may even need to call an ambulance in extreme cases.
By Dr Michelle Wright
Dr Michelle Wright (MBChB, MRCGP) is a British-trained general practitioner. She works as a doctor in the staff medical service of the International Labour Organisation in Geneva and she has a regular radio show about health on World Radio Switzerland (www.worldradio.ch). Dr Michelle is also one of the Medical Directors of HealthFirst, a company delivering First Aid Training and Health Education in English (www.healthfirst.ch) throughout Switzerland. Contact info@healthfirst.ch if you are interested in attending or organising a First Aid course near you.
Photos by HealthFirst
