Processionary caterpillars and dogs: my dog touched a hairy caterpillar, what do I do now?

Spring, a walk through a pine wood or down an avenue of oaks. Your dog stops and puts his nose to a line of hairy caterpillars crawling nose to tail across the ground like carriages on a train. A minute later he's drooling heavily, pawing at his muzzle, and his tongue is swelling and turning red. It's almost certainly the processionary caterpillar. For dogs it's one of the most painful contact poisonings there is, and one of the fastest. Its tiny hairs carry a toxin that gets into the tongue and gums on the slightest touch. Below: what to do in the first few minutes, what the vet will do, and how to stay clear of the risky places and months.

What to do in the next 10 minutes

1. Get the dog away from the caterpillars. Take hold of his harness or collar. Don't touch his muzzle and don't touch the caterpillars, because the hairs come away easily and get into your skin too.
2. Don't let him rub his face, either on the ground or with his paws. Rubbing breaks the hairs, and broken hairs release even more toxin. Keep him close to you on a short lead.
3. Rinse his mouth with plenty of water, if you've got some and he'll let you. Plain water, lukewarm or room temperature, poured gently from the side over the tongue and gums, with his muzzle tipped slightly down so it runs out rather than down his throat. Don't rub his tongue with your fingers or a tissue. If you have gloves or a bag, put them over your hand.
4. Head straight to the nearest vet, even if it isn't your usual practice, and ring ahead from the car. Say "processionary caterpillar" in your first sentence. The sooner treatment starts, the less chance there is of part of the tongue dying.
5. Watch his breathing on the way. If his face and throat swell, his breathing turns laboured and noisy or his gums go bluish, it's a severe allergic reaction and every minute counts.
6. Take a photo of the caterpillars or the nest, if you can without getting close. The vet then knows exactly what they're dealing with.

What you may see in the first few hours

• heavy drooling, sometimes frothy;
• pawing at the mouth, whimpering, restlessness;
• a swollen red tongue, later purple, grey or whitish in patches;
• swollen lips and face;
• vomiting, especially if he swallowed caterpillars or hairs;
• rarely, a swollen throat and difficulty breathing.

Look after yourself too

The hairs end up on your hands and on the dog's harness without you noticing. Afterwards, wash your hands thoroughly with lots of water before you touch your face or eyes. Handle the harness and lead with gloves and wash them on a hot cycle together with the clothes you were wearing, separately from the rest of the laundry. If you get an itchy, blistery rash or your eyes go red, tell your GP you touched a processionary caterpillar. People get a similar reaction, usually milder.

In the days that follow

Badly affected patches of tongue can die and drop off a few days later. That's why the vet will want to see him again, even if he seems to have recovered at the first visit.

What to tell the vet and what they'll do

On the phone and when you arrive

• what he touched: a line of caterpillars on the ground, a white silky nest in a pine, something on an oak trunk;
• how long ago, how close he got, whether he licked, bit or swallowed anything;
• what you've already done, especially whether you rinsed or not;
• what you can see now: drooling, how swollen the tongue and face are, how he's breathing, the colour of his gums;
• his weight, any other conditions, any medication.

What the vet does

1. Checks his breathing first. If the throat is swollen and he's struggling to breathe, the priority is keeping his airway open and stopping the allergic reaction.
2. Flushes the mouth thoroughly, often under sedation. That way the remaining hairs come out without breaking and the vet can see the whole tongue.
3. Treatment for inflammation and pain, chosen by the vet, usually by injection to begin with.
4. A drip for fluids, especially if he's drooling a lot and can't drink.
5. Keeps him under observation for a few hours or overnight, depending on how swollen the tongue and face are.
6. Check-ups over the next few days. The vet watches for any part of the tongue losing its colour. If tissue dies, it may need cleaning up. Most dogs cope well even with a piece of the tongue tip missing, after a spell of relearning how to drink and eat.
7. Soft food for a few days, mashed or soaked, as your vet advises, and water always within reach.

When you take him home, ask which signs mean you come back (the tongue changes colour, bad breath, he stops eating or drinking) and when the check-up is.

How to keep him away from processionary caterpillars

The caterpillars and their season

In Europe, dogs come up against two species, which live in different trees and come out in different months:

The hairs stay dangerous after the caterpillars have gone, in old nests, in ones that have fallen to the ground and in the grass under the trees. The pine species is common in southern and western Europe and has been moving north in recent years, while the oak species is now established in parts of southern England, London included. If you're taking your dog abroad in spring, ask the locals.

Other hairy caterpillars can irritate a dog's mouth and skin too, usually more mildly. The rule is the same for all of them: the dog doesn't sniff or lick hairy caterpillars.

Out on walks

• In spring, wherever there are pines or oaks, keep your dog on the lead and watch where he's putting his nose.
• Give trees with visible nests a wide berth, and the ground underneath them.
• Young, curious dogs who shove their nose into anything that moves are the most at risk.
• Build a reliable "leave it" at home, over weeks, on things he's not that bothered about, with praise and a tasty treat every time he gets it right. By the time you meet a line of caterpillars it's too late to start.
• For dogs who spend hours with their nose to the ground (mantrailing, gundog work, search), pick spring routes away from pines and oaks with nests. A dog locked onto a scent isn't looking at what's under his nose.

In the garden

If you have pines or oaks with nests in the garden, don't remove them yourself. The hairs get into the air and can cause serious irritation to skin, eyes and airways, in people as well. Contact the council or whoever manages the park; there are specialist firms that remove them safely. Until then, keep the dog out of the area under the trees.

What to carry

Your own vet's number and that of a 24-hour clinic near where you walk. And in spring, a spare bottle of water in your bag, because if you do run into caterpillars, that's where first aid starts.