Britain's 900 or so larger moths are divided into nineteen families of moths closely related to each other. Each family shares certain characteristics, some of which can be recognised by a beginner. In particular, members of a family tend to be a similar shape. So, when trying to identify a moth, start by looking at its shape.
The largest family, with just over 400 members, are the Noctuids. They are nearly all active at night, have powerful, agile flight and often need to refuel with nectar. Noctuids have thick bodies and a characteristic resting posture. The wings are held overlapping across the back, making a tent-like shape, and viewed from above the moth looks like a narrow triangle or letter A. Noctuids tend to be subtly coloured, often a mixture of browns and greys, but the Pink-barred Sallow is a more colourful example.
The Geometrids are the next largest family, with over 300 species. They have thin bodies and at rest most hold their wings flat in a butterfly shape. They have rather weak fluttering flight and as many fly around dusk or dawn, and some during the daytime, they could be mistaken for butterflies. The geometrids include several large sub-families, notably the waves, carpets and pugs. The family name comes from the Greek for ground-measurer, after the odd looping walk of their caterpillars.
The beautiful tiger moths are in the family called Arctiidae. Most tiger moths have dark forewings spotted or striped with white or cream, while their hind wings and bodies are a vivid red, orange or yellow. These bright colours warn predators that they taste unpleasant. Also in this family are the small slender footman moths, at rest shaped rather like pumpkin seeds, and the White Ermine and Buff Ermine which, as their name suggests, resemble fur.
The hawk-moth family are also easy to recognise. They are big moths and include Britain's largest resident moth, the Privet Hawk-moth, as well as some even larger migrants. They have fat bodies and narrow, swept-back wings for fast powerful flight. However, the Bee Hawk-moths may not be recognised as moths at all, as they look just like bumble bees, with fat furry bodies and transparent wings! This helps them avoid being eaten by predators, which assume they can sting (they can't). Another family called the clearwings use the same trick, pretending to be wasps.
For more help with moth identification, use the link to the What moth? image gallery, or download the fact sheet on identifying moths.