Friday, February 24, 2012

Vanessa pays a swift visit

Salutations! It's always a pleasure to welcome visitors :-)

A couple of days ago a dark blotch appeared on the white-washed back wall of a small courtyard in East Kent.  

On closer inspection, the blotch proved to be my first sighting of a red admiral (Vanessa atalanta) for 2012. A most congenial visitor on a sunny (but chilly) winter's day.

The name Vanessa was allegedly first coined by Jonathan Swift as a nickname for his long-time lover Esther Vanhomrigh. The red admiral butterfly was named Vanessa atalanta in 1807 by the zooloigist Johan Christian Fabricius. Perhaps he'd read Swift's autobiographical poem Cadenus and VanessaAtalanta was a mythical warrior princess. An apposite specific name then for such a spunky butterfly.

According to Butterfly Conservation, red admirals being on the wing in winter is 'real proof of climate change' affecting British wildlife. (Red admirals, clouded yellows and painted lady butterflies are our 3 migratory butterflies.) Red admirals are now overwintering successfully in the south of Britain. Before the 1990s they were only seen in the summer months, now they flutter by from January 1st to December 31st. 

I was delighted to put a tick on my butterfly bingo card so early in the year, but when I checked on Butterfly Conservation's First Sightings 2012, I discovered that one had in fact been seen in Sussex on 1st January! One down, 58 species to go....

Being ectotherms butterflies are generally pretty good indicators of the effects of climate change on wildlife. They are often called the 'canaries in the coalmine' of environmental change. They are also relatively 'easy' to monitor and record, so their range and distribution is well understood compared to many other insects. In this regard, the UK Butterfly Monitoring Scheme is a splendid data collecting effort.

Many butterfly species are extending their range northwards as the climate warms. But as some species move north into new areas, other species cannot take advantage of warmer temperatures because suitable habitat is just not there. Species with specific requirements, viz. a food plant which is rare, are most affected, being restricted to ever shrinking, fragmented habitats. A journal article about the responses of British butterflies to climate change and habitat degradation is here.

Red admiral soaking up the rays on my greenhouse in the summer

Overall though the vast majority of our butterfly species have declined alarmingly over the last half century. Almost 75% of species (including 'common' species like small tortoiseshell) show significant declines over that last decade.

Red admirals 
are however bucking the trend and increasing in numbers as more overwinter here each year. They are strong fliers (being migratory) so have the ability to cope with fragmented habitats. They also have broad habitat requirements and utilise widespread plant species as foodplants. These are all characteristics which bode well for their response to a warming climate.

Food plants for red admiral caterpillars include: stinging nettle (Urtica dioica)..... 

...small (annual) nettle (Urtica urens)...

...and pellitory-of-the-wall (Parietaria diffusa (P.judaica)). 

(BTW if you feel the need to check out the food plants for (probably) any caterpillar in the whole world, you can do so here.)

I'd left the kitchen door open and this admiral came in for a brief sojourn on the step (and a few sips of honey water) before flying off to pastures new.