Orgyia antiqua, the rusty tussock moth or vapourer, is a moth in the family Lymantriidae. The rusty tussock moth is native to Europe, but now has a transcontinental distribution in the Palaearctic and the Nearctic regions.
The hairy caterpillar is spectacular, with “humps”, “horns”, and a “tail” in a combination of dark grey, red, and yellow. The larvae hatch early in the spring, as soon as foliage starts to appear. They are easily recognized by their horn-like tufts of hair-like setae. Four toothbrush-like tufts occur along the back, and hair pencils project from the sides at the front and at the back. The body is dark grey to black, and red tubercules are along the sides and back.
They have defensive glands at the back, and wipe their setae against them to charge them with toxins. They grow to about 30–40 mm, females being considerably larger than males. In the UK, caterpillars can be found between May and early September.
Source and more info: Wikipedia