Sunday, 24 August 2014

From egg to butterfly

For the first time I have attempted to capture a metamorphosis that takes place largely unseen. For all my many photos of butterflies you might be forgiven to think that is all they do - flutter about looking pretty. However there is a little more to it all - let's start at the beginning with the eggs of the Large White (Pieris brassicae) they start off as a batch of about a hundred small almost orange eggs. Despite their other common name 'Cabbage White' they seem happy to lay their eggs on my nasturtiums and cleomes.

large white butterfly,egg

Within a few days the bright colour fades and then the young caterpillars start developing with their heads at the top of the egg. In ten days or so they hatch out, here I managed to catch the first of the batch just emerging, having eaten its way out of its eggshell.

large white butterfly,egg

And soon they are all out and about, beginning to eat the nasturtium leaves by taking tiny bites out of them.

large white butterfly,caterpillars

The bodies soon become green and grow very quickly.

large white butterfly,caterpillars

The little black dots are their excreta or 'frass'.

large white butterfly,caterpillars

Then the black spots become more prominent along their bodies. The black spots and hairs advertise their unpleasantness to birds, most caterpillars have to keep themselves hidden to avoid being spotted.

large white butterfly,caterpillars

In order to grow they need to cast off the skin covering the next larger size that has developed underneath. This is a definite disadvantage of having your tough skeleton on the outside. The large white goes through four moulting stages. The cast off skin seems to include all the black markings.

large white butterfly,cast skin

Eventually from a rapid dose of natural selection only one or two caterpillars develop to full size. They may be predated by birds or eaten alive by the larvae of parasitic wasps.

large white butterfly,caterpillars

Soon they have chomped their way through many leaves, leaving only the stalks behind, this leaf was under attack from both sides.

large white butterfly,caterpillar

In about six weeks they are ready for the magical transformation into something completely different. When the Large White caterpillar is ready it climbs up a tree where it attaches itself in the form of a chrysalis. I was fortunate to find one as they are quite hard to spot normally. In this case there was no tree close by, so it chose my front door instead; I decided it had to be moved and stuck it onto a wooden panel.

large white butterfly,chrysalis

Now the chrysalis has a far more complex structure than just a shrivelled up caterpillar. The first shot looks at the head end, and you can already begin to see hints of wing cases and antennae. The second shot shows all sorts of structures including a central ridge that are not visible on the caterpillar. So the metamorphosis is well under-way.

large white butterfly,chrysalis

My butterfly book tells me that I may have to wait until next May before it emerges, and I will be very fortunate to catch that moment, so to complete the cycle here are some photographs of the adult butterfly. If the pupa had formed a month or two earlier it may have transformed within the same year. I have cheated here, this is a female small white (Pieris rapae) rather than a large white (Pieris brassicae). The females have two spots on the upper forewing. It is surprisingly hard to catch a good picture of the butterfly as the reflected whiteness is often too strong to show up any features. The small white is easy to identify at the caterpillar stage as the eggs are laid singly and the caterpillar is plain green. There is little difference in size between the Small and Large varieties so judging just on size is dangerous. The large white has a larger and longer black corner to the upper fore-wing.

large white butterfly,butterfly

Quite a transformation from those green wriggly things. It has been proposed that the change is in fact because there are actually two different creatures in one. The caterpillar creature carries the butterfly creature's DNA and the chrysalis marks the cell-by-cell transformation from one to the other. This theory has met strong criticism, but is at least an interesting idea. However microscopic analysis shows that the caterpillar already has tiny 'placeholders' for the parts needed by the adult butterfly and at the pupa stage the caterpillar tissues become a protein soup out of which these 'placeholders' grow to form fully sized parts.

large white butterfly,butterfly

This last shot is a close-up of what might be a Large or Small white, hard to tell. The underwing in this case is creamy with masses of tiny dots.

large white butterfly,butterfly

2 comments:

Pam said...

I have really enjoyed reading this post! Good luck with the emergence next May or thereabouts of your what will be I am sure a beautiful Large White butterfly!
I had a similar experience with a Lime Hawkmoth Moth laying eggs and had a whole winter to wait for there emergence the following year. http://allmarsh.blogspot.co.uk/2013/05/update-on-lime-hawk-moth.html

Peter said...

Nice post - amazing transformation.