Glanvilles in Dorset?

Orange butterlfy with rows of brown marks
Glanville Fritillary. Photo: Mark Pike

We have had two reports recently of Glanville Fritillaries in North Dorset!The first came in on 1 June, from Melbury Down, and the second on 6 June from Compton Down.

Mark Pike sent us a couple of shots of the butterfly on Compton Down, so we can see that it is a Glanville, but sadly, it is almost certainly a release.The only place in the UK where you are likely to find Glanvilles is the Isle of Wight, though the Butterfly Conservation website does show a few other scattered sightings in the 2010-14 period, it also states the species is restricted to the Isle of Wight.

We are always rather sad to see this sort of release: the individual butterfly will hopefully lead a normal life, but it will not be able to mate and breed, so it just dies without having fulfilled its potential. Introductions or re-introductions of species are much more difficult than you would think on the surface, requiring in-depth knowledge of the butterfly, management of the site prior to the introduction and management of the site once the release has happened. The only really successful release in recent times has been the return of the Large Blue to Somerset, brought about by Dr Jeremy Thomas after much study and preparation.

Side view of orange butterfly with white markings edged in a darker colour

Glanville Fritillary. Photo: Mark Pike

We note that this is not the first time Glanvilles have been released: in 2000, they were found around the quarry on Clubmens Down and along the Wiltshire chalk downs. This seems to prove that this type of random introduction does not work: we have not been inundated with Glanville sightings over the last 19 years.

3 thoughts on “Glanvilles in Dorset?

  1. Chris

    To be fair the Glanville’s have been in the Fontmell down area for a number of years. I first saw a pic 3 years ago.

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  2. Martin Wills

    The picture is of a male, but 2019 was a good year for the species on the mainland, the 2 Surrey populations did well, with a rare 2nd Brood at one of them the flight period was from April to September as well with a small gap between the broods. The populations have also been since 2010 on one site and 2006ish at the other, they even survived the 2013 crash that ended the Somerset and Hampshire mainland populations. UK Monitored populations are very few, in 2019 there were only 333 sightings on the transects including the Channel Islands, with 74 on Mottistone Down IOW, and 57 at Hutchinsons Bank, Surrey. Both Surrey sites have shown a spread into surrounding areas, including jumps into other counties, Hampshire and Kent. The 2nd Brood larvae also made it to hibernation size by October, so entered that alongside the other larvae that hibernated in July. Web counts are normally done in the spring, so a mild winter and warm spring may give rise to good numbers in April/May/June 2020 if a small colony is in Dorset, you may well get more sightings in 2020. This species does seem to give a 60/40 male/female ratio or even more males than that in the population ive closely monitored for 10 years.

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    1. Martin Wills

      I checked the Hibernation web at one of the Surrey sites today, and the Glanville Fritillary larvae were sunbathing on the web, its a bit early, normally its mid February they wake up,

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