Saturday, 13 July 2013

Common and Local

Several people have described moths in their traps as "being Common" in the book.  It's probably worth a quick note on what that means.  As far as I'm aware the statuses in the Field Guide are derived from the number of British 10x10km squares a species has been recorded from.  Notable A = <10; Notable B = 11-100; Local = 101-?? and Common = >??.  I'm not sure what the threshold for Local vs Common is. 

Because it's a British measure, some species that are described as "Common" may be exceedingly rare in Carmarthenshire; Lappet being a prime example.  Records suggest it has never been anything but rare in most of south Wales and that it has declined in recent decades.  Similarly, that status doesn't take behaviour into account, so an MV-shy moth such as Beautiful Carpet or one that only flies in small numbers may have sufficient GB 10x10km square records to be classed as Common but would still only turn up once or twice in a year at a regularly-trapped site.

Brussels Lace is Local, but is correctly described in the book as "Locally frequent" in parts of the south-west.  It's a lovely moth, but is far less exciting in Carmarthenshire terms than a Lappet would be!

Hope that helps
Sam

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