On Red Admirals and Migration

A couple of weeks ago I wrote about the fantastic Red Admiral that I am hoping will be around and about as soon as the weather warms up.  However, the reason that I was prompted to write about the butterfly was due to an interesting article that I read in the wonderfully informative British Wildlife magazine.

Whilst many nature lovers are aware of the satellite tagging that is now being done on all sorts of species, particularly the cuckoos and ospreys that have been tracked to Africa and back, you may not be aware that there are other ways to track the movement of species (particularly small, delicate ones such as butterflies).

Scientists have recently been investigating the levels of different isotopes of hydrogen found in the wings of Red Admirals across Europe.  These are taken into the body of the butterfly when, as a caterpillar it does what caterpillars do and eats.  Across Europe the normal foodstuff of a caterpillar will have different levels of these hydrogen isotopes.  Comparison of these levels with non-migratory species of butterfly then allows scientists to tell where the butterfly spent its time as a caterpillar.

The results of the work were very interesting.   Italian butterflies examined in autumn showed different isotope levels to non-migratory species.   This indicated that the butterflies had developed in northern Europe and migrated south.  Italian butterflies examined in the Spring had levels similar to those of local butterflies indicating that they were locally bred as a result of a winter breeding cycle and were not overwintering adults from further afield.  In addition there were also some individuals that seemed to have migrated from further south in the Spring.

In Northern Europe the examination of butterflies in the Summer appears to suggest that they had migrated from central Europe, whilst those examined in the autumn appeared in the main to be more local, but with some migration still occurring from the south.

So, in conclusion it would appear that butterflies move north to breed in the Summer and then move south in the autumn to breed into the winter months.  Will this change with the changing climate  and, as previously noted, an increased propensity for adult Red Admirals to overwinter in some northern parts of Europe?

Snails – reasons to take a closer look.

Snails – curse of gardeners everywhere, something to try and remove at all costs, and dull, dull dull. As my mother would say, what use are they to anyone? Until recently I was of a similar opinion. I tried to remove them from the garden, tried to encourage hedgehogs in to help do away with them, watered nematodes around my crops (although I admit this was more to deal with slugs than snails) and generally wondered if there was anything good to say about them.
However, a few months ago I started my photography 366 project which involves taking a different photo each day. When out for an evening wander I came across lots of snails making their way across the footpath and spent far too long trying to take photos of them. I was struck by how varied they were and by the number of different colours and patterns. Being me I decided to do some research, the first port of call was my newly purchased copy of Bugs Britannica. This then led me to the internet and a new appreciation of these snails.
 So, to start with, these are banded snails – there are brown lipped and white lipped varieties (although to add to the confusion young brown lipped snails have a white lip). To set the record straight, in common with many slugs, it appears that these snails feed mainly on decaying vegetation. So, although they will munch on my french beans, it seems that the garden snail is a bigger criminal.
The variation in colouration and banding pattern also means that they are one of the most genetically studied creatures around, that and the fact that they can be found pretty much everywhere. They come in three colour varieties – brown, pink and yellow and have varying amounts of banding – as illustrated in these photos. This was a basis for a huge online citizen science project carried out in 2009.
The basis of the project was to compare distributions of the yellow and brown snails and different amounts of banding – unbanded, mid-banding, lots of banding. Observations were made across Europe and compared to historical records. The reason behind the project was to see if the increase in temperature of 1.3oC in the latter half of the twentieth century had affected  the distribution of the variations. This is because of the ‘albedo’ effect – which is a measure of the reflectivity of a surface. The theory was that as the climate got warmer there would be an increase in the number of yellow-shelled snails compared to the darker variants and an increase in the proportion of unbanded snails as they evolved to stay cooler.
So, what was the result. They separated out the results according to habitat – sand dunes, grassland, hedges and woodland. It was only in the sand dune areas that the proportion of yellow snails increased – in the other areas it would appear that there was sufficient shade and moisture that the increase in global temperature had no effect. In fact a higher proportion of yellow snails were found in the sand dunes compared to the brown and banded snails and there was a decrease in frequency of the yellow snails as the amount of shading available increased; the smallest proportion being found in woodlands.
With regards to the banding the conclusion was that the data was inconclusive! There is the potential that changes are linked to habitat and predation. As their main predator is the song thrush then changes in the distribution of the song thrush may have an effect. Changes in the habitat that are not easily captured by the survey data may also be responsible for changes. Other things may have an effect… It appears that the banded snail is retaining an element of mystery for further study.

Migrant Butterflies

When you think of migrant species, the word butterfly is not usually the first thing that pops into your head.  Whilst many of us have seen pictures of the mass migrations of Monarch butterflies in America, you may not realise that many of the butterflies that we see in our gardens each year have flown in from Europe or Africa.  (Although the recent coverage of the Painted Lady migrations on the fantastic Springwatch may have increased awareness of migratory butterflies.)

More surprising though is the fact that one of our commonest butterflies, the Red Admiral, is a migrant.  To confuse things still further though, it is also in some cases being classed as a resident.  Climate change and the warmer winters means that it is now able to survive winters as an adult in the south of the country (this includes Northamptonshire). Consequently it is often one of the first butterflies seen each year – often in January.

The Red Admiral is a striking and unmistakeable butterfly.  Its Latin name is Vanessa Atalanta, named after the beautiful and athletic goddess Atalanta, a famous huntress.  Atalanta tried to enlist with the argonauts but was turned down as Jason was worried about the presence of one woman on the ship.  She would go to such lengths to avoid marriage that suitors were challenged to a race, those who lost, the penalty not being a sufficient deterrent, being put to death.  She was eventually beaten after the love goddess Aphrodite took pity on a suitor and helped him distract Atalanta during the race.

The butterfly given her name can be seen throughout the year (although the first major migration occurs from mid-May to the end of June), in most habitats, throughout the country.  It will visit many flowers, switching from one favourite to another as the summer progresses, moving onto fruit and then ivy blossom in the autumn.  There would usually be a return migration in the autumn, but they are increasingly staying to overwinter in the south of England.

The food plant of the Red Admiral is the nettle, with the small, green egg laid on the upperside of a leaf.  When this hatches, the caterpillar uses silk to form a tent from the leaf on which it hatched, and, as it grows it pulls in more leaves to its tent and eventually makes its chrysalis in the tent.  After two and half weeks the black or yellow spiny caterpillar will emerge from its chrysalis as a stunning red, white and black butterfly.