Many species are reducing rapidly in number – five species of butterfly and sixty moths have become extinct in the UK over the last century – and if we are to reverse this decline, we need to understand why this has happened.

Butterflies also make a good “indicator species” – that is, because they are very sensitive to change, they very quickly show when something has altered to do with their habitat or the weather, often before other more adaptable species react. It is also easy to record butterflies, so they are well suited to this use. We can see from our records, for example, that some species are starting to spread north in the UK, which looks likely to be a reaction to global warming.

To monitor the progress of a species you have to record its numbers over the years, and to link this data with other information such as climate and land management. This, hopefully, leads to being able to deduce why a species is reducing (or, more rarely, increasing) in numbers. This in turn enables us to try to alter the way in which its habitat is managed, to aid the species’ recovery if necessary.

It is obvious that this monitoring and the subsequent work need to be carried out on a national rather than a local scale to be truly effective. In 1992, the Government signed up to the Biodiversity Treaty at the Rio de Janeiro Summit. This led to its commitment to give wildlife conservation a higher priority, a commitment to which many wildlife organisations, including Butterfly Conservation, were quick to react.

The result has been a series of butterlfy and moth Species Action Plans and Habitat Action Plans (leading to Regional Action Plans!) which have defined which species are under particular threat, what can be done to help them, and the cost of the necessary action. This, for the first time, gives us targets against which to judge our – and the Government’s –  success.

Since 2006 the British Government has recognised that butterflies are good indicators of the state of wildlife generally and the United Kingdom Butterfly Monitoring Scheme now provides a series of trend graphs dating back to 1976 and updated annually . These show the state of the commoner butterfly species found in the wider countryside as well as the rarer ones which need specialist habitats. The UK BMS website is where you can see the many different ways in which this data is used.

But who can do all this monitoring?  The answer is that a lot of it is done by amateurs who volunteer their time.  Entomology is one of the areas of science where it is still possible for the amateur to be heavily involved and to make a real contribution to scientific knowledge. Butterfly Conservation organises huge amounts of butterfly and moth recording, and the accumulated data is making significant contributions to science.