Thursday, 26 May 2016

Glanville Fritillary

I made a return visit to Hutchinson Bank today to see how the Glanville Fritillary colony was progressing. When I visited in 2014 the colony was only just becoming established and despite an extensive search I could only find one butterfly, a female. Today I saw somewhere in the region of fifteen to twenty of them. I am told that the transect is showing twenty four and that we have not yet reached the peak emergence.

This is the rarest of the UKs butterflies with only this colony and one on the Isle of Wight. It is on the northernmost edge of its territory and a bad winter, parasites, or other threats could see it become extinct in this country.

Attempts, by persons unknown, have been made to establish other colonies. These have been at Sand Point in Somerset, Avon Gorge, and Wrecclesham in Surrey, probably using stock imported from the continent. All these colonies seem to have died out, although they are not declared as such, until they have completed three clear years without sightings being made.

There have also been short lived colonies at Hurst Point and other locations on the Hampshire coast but these could well have been seeded by migration from the Isle of Wight.

The population of the Isle of Wight colony fluctuates wildly. This may be due to bad weather or perhaps the impact of parasites that exist alongside the colony. Parasites that at the moment do not appear to be present at Hutchinson Bank.

At the moment it looks like another bad year for the IoW with very few sightings being made so far. They should recover, weather, if that is the cause will improve and it is rare that a parasite wipes out its host completely. If anything should happen to it, at least we now have Hutchinson Bank as a back up holding UK stock.

Update: Good news - fifty plus Glanville Fritillaries reported on Compton Cliffs on the 29th May.

Are the Hutchinson Bank Butterflies real or "plastic"? Well the colony seems to be self sustaining with eggs, caterpillar, chrysalis and imago all being found at the site. However, there is a butterfly house and breeding program to provide a back up to the site. 

Evidence of natural breeding at the site is shown below.

With plenty of the caterpillars food plant on the site it looks as though next years generation are safely on their way.

See my blog of May 2014 to find the story behind the naming of the Glanville Fritillary butterfly.

and below my first Small Blue of the year

Small Blue

See a recent blog by the warden for the site, also a Martin, for some more great pictures and in particular for a shot of an aberration ab.wettei. It would be worth going back just for the chance to see one of these.

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