Counting butterflies

As the butterfly season draws to a close, butterfly surveyor Janet Ritchie reflects on the 2017 survey season and the all important Dartmoor weather...The regular butterfly transect through Yarner Wood takes place every week from April 1st to September 30th. The same timed walking route is used for long-term comparisons over the years. One of the main weekly considerations is the weather, the temperature has to be between 13-17 degrees and not when it’s windy. This keeps us focused on the forecasts for the whole six months. This year the first week started on Saturday April 1st, so we go for every Saturday, with back up over the following couple of days if rain gets in the way, as it often does.

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Silver-washed Fritillary and Red Admiral - are both species recorded in Yarner Wood (Photo credit: S-wF, Natural England/Allan Drewitt, RA, WTPL/Jane Corey)

We can't tell how many butterflies we may find. It can vary a great deal, for example the first four weeks gave us between 8 and 14 butterflies in total. Week ten in June only 3, and two weeks later just 4 butterflies in 100% sun. A week in July with far less sun came to 81. Numbers vary greatly and not necessarily for obvious reasons. Into mid-September and the count was down to 2. The species recorded vary as the year progresses.

The transect around Yarner is always enjoyable and good exercise. The area recorded is up to 2.5 meters either side of the route line and 5 meters in front of the recorder. Over time, it becomes clear that some sections of the route are likely to produce more butterflies than others, possibly down to recent rain, potential food sources and the ratio of sun to shelter. The time of day can also be a factor, walks have to be done between 10:45 and 15:45, again for consistency.

Speckled Wood - a butterfly beautifully camouflaged for dappled shade and woodland rides Photo: WTPL/Glyn Baker

Once all the records are done, I record the season's data for Butterfly Conservation on the UK Butterfly Monitoring Scheme website, by the end of October. This adds to the overall picture of butterflies in general and how they are faring each year. Different habitats also give different results, as I discovered on a recent visit to west Cornwall, where I was literally surrounded by dozens of Speckled Wood butterflies along the cliff bridleways. Fascinating stuff!

Written by Janet Ritchie, Natural England volunteer

Photo credit for header image: Speckled Wood, WTPL/Amy Lewis