Data collected by the 10,000 UK butterfly recorders is invaluable. The findings are published and create a national map which informs Government and conservation bodies where conservation effort needs to be directed.

The database is the largest of its kind in the world, containing over eight million butterfly records, from as far back as 1690 to the present day.

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Butterflies for the New Millennium is the butterfly recording scheme for the British Isles. It is organised in the UK by Butterfly Conservation and the Biological Records Centre and in the Republic of Ireland by The Dublin Naturalists’ Field Club.

A record is made up of a number of separate pieces of information, many of which can be given at different levels of accuracy.

The essential information which is needed to fulfill the aims of Butterflies for the New Millennium is explained at some length on the recording forms at the bottom of the page.

One of the most important pieces of information is the location of the sighting. This is recorded as a grid reference by refering to a map.

Sites and colonies

The main aim of the BNM project is to record and map butterfly colonies. These are generally correlated with sites, which range from roadside verges to forests.

It is only at site level that conservation can take place. It is convenient to use a grid of squares (10km, tetrad or 1km) to define areas to be searched for colonies.

For more populated areas, such as much of southern England, a grid of tetrads is a convenient way to target recording; in upland/highland areas a 10km grid is more practical.

Aim to visit sites in as many squares as possible, always identifying records from individual sites with at least 1km square accuracy and preferably 100m (six-figure), so that the data can be used to support conservation work.

It may well be that in many tetrads, three out of four 1km squares may have no useful habitat and records may come from only one 1km square.

Record the grid reference of the site or at least the 1km square and not the tetrad reference. Large sites, such as major forests, should be subdivided into 1km squares or sub-sites for recording.

Timing of visits

You should try to visit each site at least four times, preferably in early May, mid-June, mid-July and the second half of August, to catch the flight periods of all possible species.

Warm sunny weather between mid-morning and mid-afternoon is ideal, although some species may fly earlier and later in hot conditions; in cool overcast conditions you are unlikely to see butterflies in flight, but they may be found resting.

Re-visits to sites are also valuable to record species whose populations vary widely from year to year.


It is important that records are accurate.

There are several good field guides available to help with identification of species. If you are in doubt about an identification it is best not to record that sighting.


Try to find examples of different habitats to visit in your area e.g. woodland, grassland, farmland and heathland. Each will support a different range of butterfly species.

In intensively agricultural areas, search for unploughed headlands, hedgerows, relics of woodland, tracks and footpaths.

Set-aside areas and some roadside verges often provide suitable habitat for many species. In urban areas parks, gardens, churchyards and ‘waste’ ground often provide suitable habitats for butterflies.

For urban areas, parks, gardens, churchyards and 'waste' ground may provide suitable habitats for some species. Former industrial sites, old quarries and disused railways can be rich in butterflies, but please check that access is permitted and that sites are safe before visiting.

Access to sites

Ordnance Survey maps display public footpaths and rights of way very clearly; you should stick to these paths wherever possible.

If you need to enter private property whilst carrying out field work, you must seek permission from the landowner first - this project does not convey any rights of access to private land. It is also important to respect the Country Code at all times.

Recording forms

For repeated visits to a particular site use the Site Recording Form. The Casual Record Form is used to note records from scattered locations.

Please enter on the recording form your name and address (or that of the recorder), the site name (or the name of a local geographical feature) and the grid reference of the site or locality. Please indicate also the type of habitat, using the codes listed on the form. Please note the date of the visit. For each species seen, record the numbers seen at that locality. Full instructions are given on the forms.

Where unusual or threatened species are recorded, it is useful to give as much detail as possible of the locality so that follow-up visits can be made to assess conservation needs. Space for comments is provided on the forms.

Send completed forms promptly at the end of each recording season for computer entry to your local co-ordinator (usually printed on the forms) or to Butterfly Conservation at the address below.

Recording, mapping and grid references

For recording to provide effective data for local purposes, such as planning and conservation work or national analysis of how particular species are faring, records have to be related to sites.

Therefore, the grid reference for any butterfly record should be to at least 1km square accuracy (four-figure grid reference), and preferably six-figure references which pinpoint a sighting to a  100m x 100m square.

When it comes to mapping butterfly records data are often plotted in a summary form on distribution maps e.g. as tetrads (2km x 2km squares) for local maps, or 10km squares for the national scale.

Generally atlas organisers seek to ensure that some recording is carried out within each tetrad or 10km square, to give a good level of mapping coverage.

How to work out a grid reference

Please use only the National Grid references from Ordnance Survey maps - not road maps, which may have non-standard grids.

1km squares are marked by a grid of light blue lines on 1:50,000 series (Landranger) OS maps. The grid reference of a 1km square consists of the 100km square code (e.g. NN), which will be marked somewhere on the map, followed by four numbers, which mark the bottom left-hand corner of the square (see example below).

The first two numbers refer to the horizontal (East-West) scale and the second two the vertical (North-South). It is very important to put these in the right order.

100 km square code: NN | Shaded 1km square: NN4893

A 6-figure (100m square) grid reference is derived by dividing the 1km square into tenths, from the left (west) and the bottom (south).

For example, the map reference of the cross in the shaded square above is given by combining the east-west reference, 482, with the north-south reference, 937, giving a full reference of: NN482937.

When you move into another 1km square, record sightings there separately, so that important sites can be correctly identified.

If you do not have access to suitable maps or are not familiar with grid references, please do not be put off from recording the butterflies which you see. Contact your local co-ordinator and they may be able to help.

Download instructions as a PDF