My Butterfly Year on the Two Tunnels Cycle Path

Gatekeeper Butterfly - July 2018

I have to admit that when I set out on this journey I did not imagine the diversity of butterfly species I would encounter. My memories of this abandoned railway track from the 1960's are very different from the cycle-path of today. Back then it was more open, sunny and far less wooded area and the section between Tucking Mill and the abandoned Midford station was not easily accessible until the cycle-path was opened in 2013.

Over the course of the spring and summer I have made twenty-one trips along the 'Two Tunnels' route From Bath to Tucking Mill and Wellow. Along the way I have counted over 700 butterflies of 26 different species. 

Click here to enlarge

There have been some surprises. One of the highlights of the year was the number of Silver-washed Fritillaries I encountered. Between the 28th June and the 8th August, I managed to count 33, mainly around the Tucking Mill section of the path. That's a higher count than Red Admiral, Small Tortoiseshell and Comma all of which were disappointing this year. To 'top it off', on the 1st August a 'Valezina' form of this butterfly presented itself to me on a Buddleja bush near Midford. Always a treat for any butterfly enthusiast!

Silver-washed Fritillary (var. Valezina) Midford - August 1st 2018

I was also pleasantly surprised to find White-Letter Hairstreak butterflies at three different locations along the route. Having, earlier in the year, spotted several large flowering Wych Elm trees growing near the path, I speculated on the possibility that I may see some of these butterflies later in the year. It has been a decade or more since I have seen them in the Bath area, so it was great day for me when I did finally manged to see them. The main concentration were centred on a large mature Wych Elm growing on the embankment near Midford Castle. I spent sometime watching several engaging in 'aerial combat' around the crown of this tree! There are numerous smaller Wych Elm saplings growing along this stretch of cycle path, both between the tunnels and out towards Midford which could provide suitable breeding sites for this enigmatic butterfly.

White-letter Hairstreak July 2018 - Tucking Mill

Another enigmatic butterfly, and one of great conservation concern, is the Marsh Fritillary. When I started my walks I was aware that this butterfly is known to be present in the Tucking Mill area, having been identified in its larval stage by a Wessex Water Ecologist in 2017, and reported in the local press. It was still a real treat when on the 22nd May a courting pair of these butterflies flew past me on the a grassy embankment adjoining fields owned by Wessex Water. Using my binoculars from my vantage point on the embankment, I could make a positive identification of several more, further into the field. During August and September I returned to this section of the embankment to see if I could spot any larval nests on the cycle path side of the fence. Sadly I could not. There are only a few suitable Scabious plants present and these were rather shaded out by the tall grass growing there.

Embankment adjoining Wessex Water land - Tucking Mill 

One thing I have learnt is that counting butterflies accurately is not easy. I cannot say that my 'counts' were rigorously accurate, although they do reasonably accurately reflect the range of species seen and their relative abundance. I encountered two particular problems. 2018 was clearly a bumper year for the 'Whites'. Green-veined, Small and Large White butterflies were numerous and very active all year. However it is very difficult to accurately distinguish these three species in flight! I decide to only count those I could identify once settled. Consequently the numbers of these three species I recorded are hopelessly low, but the relative proportions are likely to be pretty accurate. 

Meadow Browns and Ringlets are much easier to identify accurately as they are much more likely to settle and when fresh, fairly easy to distinguish in flight. However, here was another problem. Between the 22nd June and the 10th July these butterflies were just so numerous it was impossible to count them accurately over an even moderately wide area. Many were flitting between bramble blossoms by the dozen. My strategy here was to 'sample' numbers in a relatively small area and thus get an idea of the relative abundance of the two species on each date I counted.

Meadow Brown - The most numerous butterfly on the route

There was one butterfly I did expect to see given the numerous Oak and Ash trees along the path. Purple Hairstreaks are not uncommon in the Bath area, and I did almost expect to see some here. However it was not to be. Unlike the White-letter Hairstreak they are reasonably easy to spot with a little practice given the greyish undersides to their wings. They give a silvery flash when viewed from the ground unlike the generally dark appearance of the White-letter Hairstreak. I would be surprised if there are not some still lurking near Tucking Mill that I wasn't able to find!

Cycle-path at Tucking Mill - A secondary location for White-Letter Hairstreak 

 All my sightings were recorded using my mobile phone, Butterfly Conservation's iRecord Butterflies App and the the results uploaded. Nearly all the photos in this blog were taken with my Samsung S7 smartphone. This proved an efficient way of recording most of my sightings. Smartphones such as this are more than capable of taking close-up photos for identification and recording purposes and are quick to use for both stills photos and short videos. It only really started to struggle when you need to get really close or where a good zoom is required.

It been a really enjoyable butterfly year for me. Surveying this area in detail after so many years and seeing so many different species has been a real eye-opener. I will certainly re-visit this stretch of the National Cycle Network over the coming months and will be looking forward to seeing many more butterflies and other creatures next year.