Nature Studies by Michael McCarthy: We all know it has been mild recently – but butterflies think it's spring

Here's a remarkable butterfly story. When you first become interested in butterflies, you naturally enjoy their vivid colours and concentrate on recognising them, but as you become more involved, you start to look at subtler things.

One is the larval food plant of each species; if that plant isn't present for the caterpillars to munch, it's not very likely the butterfly will be. So, the caterpillars of several of our bright, orange-and-black fritillaries feed on violets, and a wood without violets is likely to be fritillary-free.

Another is the species' scientific name, which will usually tell you something interesting about the insect (once you translate it from the Latin). Thus, the second part of the scientific name for the black hairstreak, Satyrium pruni, tells you it feeds on blackthorn bushes (Prunus).

But one of the most interesting aspects is the species' overwintering strategy. Think about it. We see our butterflies mainly in the summer sunshine, but only two of our 58 species are immigrants from Europe's warm south: the painted lady and the clouded yellow. From one year to the next, the other 56 all have to survive the rigours of our winter.

There are four ways they can do it: as an egg, as a caterpillar, as a pupa or chrysalis, or as a fully formed adult insect. Here's a piece of knowledge for when you're on Mastermind with butterflies as your specialist subject: 31 of our 56 species spend the winter hidden away as a caterpillar; 11 spend it as a chrysalis; nine go through it as an egg; and a mere five pass the cold season as an adult butterfly.

These five are the peacock, the small tortoiseshell, the comma, the red admiral and the brimstone (all fantastically handsome). Four of them perform a fascinating camouflage trick: with their wings closed, they look like leaves. The first three, all closely related, are convincing dark-brown dead-leaf imitations, complete with crinkly wing edges, and this can make them invisible when they are hibernating in a wood pile or your garden shed. The red admiral, which has only started overwintering in Britain in the past 20 years, is not quite so dead-leaf-like, but the lower underwings are dark and cryptic, and certainly less easy to see against a dark background. The brimstone is different again; it looks like a pale green leaf and has been found hibernating in evergreen ivy clumps.

It is because they overwinter as adults that these five butterflies are the first ones we see when the warmth returns. They have no more growing to do; they wake up and start flying about at once, to look for mates. Although I think of the brimstone and the orange tip (which overwinters as a pupa) as the first true spring butterflies, and look for them from March onwards, it is often an overwintering peacock that you will first see.

And here's the point: this year, the weather has been so mild that all five have been observed flying about in the first week of January (or, to be strictly accurate, the first eight days). On 1 January, a red admiral was seen in Sussex; on the second, a peacock in Sussex and brimstones in Hampshire and Surrey; on the sixth, a small tortoiseshell in Sussex; and on the eighth, a comma in Norfolk.

According to Martin Warren, head of the charity Butterfly Conservation, this is unheard of. "It's a remarkable event," he says. "We have no records of it happening before." You can find the details on the charity's website, www.butterfly-conservation.org.

You might have thought it's been unseasonably warm in the past couple of weeks; but not half as much as our butterflies have.

Mole-watching for beginners

I wrote last week about my ambition to see a mole, and as with the previous "Nature Studies" about the writer BB, and his saga of the last gnomes left in England, I was taken aback by the response. I had no idea so many people were mole-conscious. Thanks to everyone who emailed: this is from Chris Lily, whose cat brought a mole into the house.

"He dropped it... and sat back while we watched it zip under the hearth rug, across the carpet, and into the sofa through a hole in the bottom. I rescued it when it found a route between the covers and the cushioning...

"When I got him out and held him, he was so beautiful – amazing paddle feet, tiny pin-like eyes, hyperactive nose, and the feel of such a tiny muscly body covered in velvet, so soft, so warm, so strong. It's a sensation I will treasure for ever. I took him out into a field and watched him take a breath or two then swim down into the soil. Quite amazing and quite wonderful. They are absolutely brilliant creatures, and while I'm sure you wouldn't elect to hold one for fun, it's a great thing to have done out of necessity."

m.mccarthy@independent.co.uk