Tuesday, December 27, 2011

Diary of a butterfly

Note: To all those who suffered the indignity of non-notification of new posts, followed by my attempts to notify you myself and then probably getting notification after all-I apologise and I am pretty sure I've fixed the problem now.

With British butterflies being in decline and 2011 not being a good year in general it was a real joy when out walking on April 7th to find my first Orange-tips (Anthocharis cardamines) a few females.

Orange-tips are a true sign of spring and one of the first species that does not overwinter as an adult to emerge.

These butterflies will use Cuckooflower (Cardamines pratensis) both as a nectar source and for egg-laying. I spotted the first Cuckooflower actually in-flower on March 20th, having already seen Violets and Wood sorrel.

On April 9th I saw my first  males. I had already come across Peacock, Comma and Speckled-wood butterflies by this time.

It's only the more-conspicuous male that has this orange tips to it's wings, with the female often being mistaken for one of the other 'whites' especially the small white.

The Orange-tip Butterfly (Anthocharis cardamines)

By as early as April 15th I was already finding eggs on the Cuckooflower. 2011 did produce an exceptional spring with some stunning temperatures and long-hot days, on the 7th for instance, I recorded 20 degrees.

When searching out suitable plants on which to lay her eggs, the female will initially locate a plant by sight before alighting on the plant and tasting it with her feet. If the plant is suitable, a single egg is laid on a flower stalk. Eggs are laid singly for good reason – the larvae are cannibalistic. As a result, it is uncommon to find more than one egg per plant and it is believed that the female is able to detect eggs that have already been laid.

The portion of text above in italics I gleaned from ukbutterflies.co.uk a great source of information, as with all literature on the subject though, it should be read as an overview and not a 'bible' as there will be deviations as in all of nature.

A recently laid Orange-tip ova
Eggs are a greenish-white when they are first laid, they then gradually turn yellow, to orange and then eventually colour-up further showing the larva colours,with the larvae emerging after anything between one and two weeks.
Interestingly, although according to U.K. Butterflies it is uncommon to find more than one egg per plant, I did find at least two eggs on some plants this year.
2nd & 3rd stage eggs
The photo above clearly (well not that clearly actually) shows two eggs on the same plant and at different stages of development and as I've read that females will deposit a pheromone to deter future females,wonder if these were actually laid by one individual on different days, or just developed at a different rate as larvae do.

The other thing about these eggs is that they were laid not on Cuckooflower but on Winter-cress (Barbarea vulgaris).

As I understand it, winter-cress is  biennial  and so it seems strange to me that the butterflies would choose it to lay eggs on, knowing that the larvae would feed on the plant after emergence and yet being biennial, would there be any plant to feed on?

Once the eggs become this brilliant orange colour the next thing that happens is the appearance of darker spots, as shown in the photo to the left. This particular shot was taken on the 18th April and shortly afterwards the egg changed again to a darker, mottled colour that was a sure sign that emergence of the larva was imminent. I'd been keeping an eye on these eggs for quite a while in the hope of being fortunate enough to catch a photograph or two of either the tiny larvae emerging, or perhaps the newly emerged, first instars (there are 4 moults in total), or even if I was really lucky, both. Providing of course that my skills with the camera would be consummate enough to capture anything this small worthy of sharing. 

Almost cooked

  Well I didn't have to wait too long, on April 19th when I did my early morning check on the eggs, some minute larvae had already emerged and were going about their business of finding food-something that would occupy them for the next 3 to 4 weeks.

A first instar larva
As you can probably tell from the photograph above, the thickness of the Cuckooflower stem the larva is on would be no more than a few millimetres wide and the caterpillar is only around one third of that and so obviously very small.
They are also on emergence this kind of translucent amber colour but will gradually change with each moult to the more recognisable green/grey of the adult larva. Once free of the egg, the young larvae will eat the eggshell and also in a cannibalistic manner, any other eggs in the vicinity. From observing them this year, I noticed for the first time that they will also eat the exuviae produced at the moult stage-this was particularly interesting to watch and record being a first for me.

A later stage caterpillar eating the moult

Notice how in this later stage caterpillar the colouring has already undergone a change towards green.
I continued to watch and record the caterpillars and noted that they seemed to feed mainly on the developing seed-pods as well as leaves and even the flowers.
With each new moult they seemed to be acquiring both the recognisable colour of the adults along with an increasingly good camouflage.
By April 14th I measured one at just a little over 25mm         


Once the larvae have reached maturity the feeding seems to increase until it seems to be just about all they do (well that and poo!) but eventually the frenzy abates and their metabolism seems to slow until they become less frenetic and begin to leave the food-plant in search of a pupation site.

The larvae are known to travel extensively in search of a good pupation site and that usually means a scrubby area with lots of low undergrowth where they can safely spend the winter.

The start of pupation showing the silk girdle

When the perfect spot has been located by the adult caterpillar it will climb a plant stem and begin the process of pupation by attaching itself to the plant with it's rear end by means of the cremaster, a cluster of minute hooks used to grip and then forming an arc, head-down.

Orange-tips belong to the family 'Pieridae' and all of this particular family use a silk girdle sewn by the caterpillar itself to hold the pupa steady.

Soon the caterpillar begins to undergo some amazing changes-this is a truly absorbing thing to watch as the head-end morphs into a completely different creature that on one hand somehow reminds me of those fabulous eastern jade figures, and yet on the other, even at this early stage, there are clear signs of the butterfly taking shape.

In the above close-up shot, the head,wings and what will be antennae are already clearly defined; just amazing to me, how can something change shape before your eyes? It's not even like the final process where the old body of the larva gets broken down into a kind of soup and then reforms within the chrysalis, I can understand that to some extent. If you stood and watched long enough, you could actually watch this take place.

Orange-tip pupa
Eventually the caterpillar is completely transformed into a pupa and it will now remain in this state through the rest of the season, right through winter and into next spring before a butterfly emerges to start the whole process over.

A mature Orange-tip pupa

Over time, as the pupa hardens it begins to change from green to cream/white, a colour much better suited to the winter surroundings and therefore increasing it's chances of survival.

And so that's where we must leave the story of the Orange-tips for this year. It was actually a good year for this species locally as it was for Ringlet but numbers of Common Blue and Comma were well down.
I would very much like to be able to photograph the emerging butterflies next spring to complete the whole process of metamorphosis but right now, that's over 3 months away, we have winter to contend with first.

Until the next time then...

No comments:

Post a Comment

Please feel free to comment on my blog. I am always grateful for any feedback, good or bad. Commenting should be fast and easy. Just enter your comment in the box, then click on the drop-down box beside 'Comment as'. You can use your Google ID if you have one, or just choose 'Name/URL and enter your name (URL is not needed). You can also just choose anonymous, if you would rather not be identified.

Regards 'JJ'.

If you do experience any difficulties, you can contact me directly from this blog and I will try to help.