Saturday 18 January 2020

Small Tortoiseshell

Today we woke to a sharp frost, a frost which lingered in sheltered, shady places all day. Yet oddly enough it produced my first butterfly of the year.


It was a Small Tortoiseshell, Aglais urticae. Chris was the first to spot it, flitting up and down on the inside of the bedroom window. (The butterfly was flitting, not Chris). She was all for letting it go free but I didn't give much for its chances outside.


Small Tortoiseshell on the inside of our bedroom window. Stefen Hill,
Daventry. 18 January, 2020
Presumably the insect had been overwintering behind a cupboard or some such structure and I hoped it might spend a few more weeks inside.

Thomas Muffet (1553-1604), whose daughter Patience appears to have been the original Little Miss Muffet, was aware of this habit of spending the winter indoors, observing 'how commonly they (are) found in houses sleeping all the Winter like Serpents and Bears, in windows, in chinks and corners. Where, if the Spider do not chance to light on them, they live till the Spring.' (Reference 1) It is tempting to assume that they once tended to overwinter in hollow trees and so on but I can find little evidence for this.


Numbers of the Small Tortoiseshell seem to dropped off significantly in the 21st Century and one reason may be down to the increasingly common Sturmia bella. This fly belongs to the Tachinidae family. Whenever I net a tachinid fly I am always pleased as they form a fascinating group but unfortunately Sturmia bella lays its eggs on stinging nettles, the main foodplant of the Small Tortoiseshell. In feeding, the caterpillar swallows the egg of the fly which hatches inside the unwitting host and eats it alive.




Tachinids are invariably (?) parasites on creatures as diverse as stick insects, scorpions and centipedes (Reference 2).  They are potentially valuable for the biological control of various pests - but I wish that butterflies were free of them!

A north country name once applied to the Small Tortoiseshell was The King's Drummer. Those drums must now be a little muffled.


References

1. Quoted by Peter Marren in Bugs Britannica, Chatto & Windus, 2010.


1. Belshaw, Robert (1993) Tachinid Flies Royal Entomological Society.


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