Sunday 4 October 2009

Small Tortoiseshell butterflies

A couple of weeks ago I did the usual annual compilation for 2009. I have compiled my butterflies records and submitted them to the local Butterfly Conservation recorder since 2003. It has been a super butterfly year. I recorded a total of 17 sp. within the boundaries of the City of Hull. One of the most noticeable species  this year has been the Small Tortoiseshell. This Small Tortoiseshell was the first butterfly I saw this year, after the long, cold winter, sunbathing on the pavement on a busy street.
There has been a lot of talk about the population decrease in this species, possibly due to mortality due a newly arrived parasitoid tachinic fly, Sturmia bella. This fly has been found to parasitise up to 40% of south England Small Tortoiseshell caterpillar clusters. There seem to be additional reasons, as this butterfly shows marked cyclic population fluctuations even before the fly was recorded in the UK.

 The graph above shows the collated results extracted from the UK Butterfly Monitoring Scheme 2007 report (well worth browsing if you like butterflies).
Despite all this, 2009 has been the best Small Tortoiseshell year since I record butterflies.
This is my total year count graph, showing the 'rebound' of the Small Tortortoiseshell after the 2006 'low'.
This is the phenology of this species in Hull.

It seems likely that there are two broods a year.
I discovered a great butterfly site, packed with info and with superb photos:

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