Tortoiseshells in April...

Small Tortoiseshell, Lower Bush, April 1st.

Small tortoiseshell larvae and old larval tent, 23rd April 2017

These once-common butterflies are sadly in decline, largely thanks to a parasitic fly Sturmia Bella. These disgusting brutes have found their way over to the UK from continental Europe and have survived due to our milder winters these days. They lay their microscopic eggs on the nettle leaves where the caterpillars are feeding.  The caterpillars ingest the eggs, which hatch out inside the caterpillar. The fly larvae eats away the caterpillar's insides, but not so much as to kill it before it pupates.  Once the host caterpillar pupates, the fly larvae eats its way out of the host and slithers off to pupate itself.

Caterpillar losses can be 100% from a colony such as above, although fortunately this lot seemed to escape parasite attack and seemed to produce a fair number of adult butterflies given be the numbers I saw in May.  I took a dozen or so of this colony and raised them all to adults, releasing the butterflies just to try and make sure there will be a few around to keep the local population going.

All of the nettle-using butterflies (Small tortoiseshell, Peacock, Red Admiral and Comma) suffer from Sturmia attack, but the tortoiseshell and peacock are hit worst because the caterpillars live in colonies, making it easier for the fly to pick them out.