Very important post about a dangerous caterpillar that is starting to emerge even earlier this year.
They are called Processionary caterpillar and live in Pine (and Oak trees too although a slightly different species).
They are very very dangerous. If you see them processing in a long line connected, leave them well alone and make sure no-one, animal or human goes anywhere near them. The hairs contain a toxin at the end which necrotises soft flesh so a dog eating one or even getting one on its tongue could die. Many do. We had a client who lost four dogs in one morning after ignoring our advice. Don't stamp on them, don't pick them up with gloves (they can expel hairs) don't burn them. If they are still in the tree in a nest and you can reach it safely, spray the nest liberally with hairspray which will help contain the hairs, then carefully cut off the branch and burn the whole thing in a lidded incinerator. Leave them in place until at least June. You can then either chop down the offending trees (they will die anyway over a period as the caterpillars eat all the needles) OR if you have missed them processing, then fit a pheromone trap to catch the moths before they lay eggs later in the year. Do not underestimate them.
If you suspect your animal has had contact with one, symptoms will be pretty much immediately.
There will be pain, and significant inflammation around the animal's mouth and nose. Tongue necrosis can rapidly develop and could even cause some parts to fall off.
Contact with the dog or cat's skin will cause an aggressive rash with multiple red spots. Itching and swelling of the affected area also often occur.
The urticating hairs can seriously damage the eyes, and any contact with eyes is very dangerous and very painful for the animal. The hairs can cause inflammation of the conjunctiva and the cornea resulting into corneal ulcers. Without being treated properly, they can even cause complete loss of sight.
If you suspect your dog has touched one, rinse the area thoroughly with water WITHOUT rubbing which could cause more hairs to burst. Then get to the vets as soon as possible. Consequences can be serious and irreversible for the cat or dog. When treated rapidly, the chance of a full recovery without long-term effects are much better. If you have apis mellifica 200c on hand (homeopathic remedy from the pharmacy) feed it to your dog straight away. If you can only get 30c, then feed at least 7. You can't overdose the dog and it really will help with the initial reaction while you get them to the vet.