I have been wanting to nurture caterpillars into butterflies for some time, but never quite found the right opportunity. Yet, as life is, things happen when you least expect them. This story starts with the mysterious destruction of a healthy pot of crisp rocket and ends with a flutter of butterflies and thoughts on reincarnation.
Rocket, with its distinctive aroma and crisp peppery taste, is an essential to any truly good salad. Admiration for the jagged rocket leafs dates back to at least ancient Greece, where it was praised for its flavour and medicinal properties. As we found out, this versatile plant is also loved by the very small, highly mimetic and insatiable caterpillars of the Pieris rapae species. This love is so great, that over just two days our pot once brimming with lush green leaves tuned into a bare and miserable landscape of stumps and half eaten blades. By the time we realised what was causing the sudden disappearance of our much loved rocket, about twenty green and friendly looking caterpillars had made it its breakfast, lunch and dinner and were scrambling around the pot like they owned the place. Now, the problem is that whilst we both love butterflies, we are also very fond of rocket, so we found our two species competing for the same space and natural resources. After a brief moment of confusion, we decided that the best thing to do to keep everyone happy would be to release the caterpillars out in the wild, somewhere that would not compromise our lunch. So we collected them up and placed them in a couple of food containers to take out into a park and release on a suitable food plant.
Unsurprisingly, the first park we went to had no wild garlic, rocket, cabbage nor lettuce growing around for our caterpillars' pleasure. Undeterred, we headed to a local market and gathered a healthy bunch of lettuce whilst we planned where else we could release them once fed. However, upon returning home, we found our caterpillars had already started to form a fragile chrysalis around their bodies, which marks the beginning of the process of transformation from pupa into butterfly. Their once smooth and long green bodies were now short and stumpy, motionless and wonderfully suspended by a very thin and transparent web. They had now turned into chrysalises, the temporary vessels which host one of Nature's greatest transformations.
From this moment, the magic is hidden to our eyes. We see nothing and hear nothing, but are only left to imagine what could be happening in that very secret space where one animal turns into a different one, through a process known as complete metamorphosis. For as long as humans have been able to observe and interrogate nature, the mystery of the butterfly transformation has been one where science and imagination met in the middle. It is only in recent years, thanks to high resolution 3D scans, that we are able to visualise this process into its finer details. Have a look at this video from research conducted at Manchester University, which makes this invisible transformation visible. For our "small white" the process lasted just four nights, during which a vast number of cells from the caterpillar's body were broken down into their constituent proteins by the release of enzymes. Whilst some of the caterpillar organs stay intact or are just partially altered (such as the trachea), the rest disassemble completely, providing the building blocks and energy to fuel the production of new cells. This primordial soup is rearranged according to previously dormant genes, so called "imaginal discs" which awaken during the pupal stage and contain all the instructions needed for the cells to go and form those colourful wings, slender legs, big round eyes, long proboscis and sex organs found in a butterfly. Is this the birth of a whole new creature?
As you can imagine, there have been heated scientific debates on this very topic. Do the caterpillars die inside the chrysalis? Is a butterfly a new being, a reincarnation, or a more flamboyant version of the old caterpillar?
Well, there is a death and rebirth theory, which states that the caterpillar has to die in order for the butterfly to be born and so that in a way the two stages represent the lives of two different creatures. The theory proposes that a very long time ago a worm-like creature and a fly-like creature engaged in some unholy procreation and somehow their genes fused and lived together in their descendent. This mutant offspring initially lived happily in the form of one of the parent's DNA until it died, dissolved and gave way for the other winged creature's DNA to take flight. Essentially, according to this view, a caterpillar is born from an egg and dies in its chrysalis and from its ashes (or juices) a butterfly is born. This might sound absurd at first, but it isn't so crazy if you know just how many times this has happened before. The protozoan Euglena gracilis for example contains three sets of genes, one in its nucleus, one in the mitochondria and a third one in its chloroplast. When these protozoa are raised in the dark and fed organic compounds, they become scavengers, meaning they feed on sugars and other organic compounds they find. However, when light is shone onto them, the algae-derived DNA in their chloroplasts becomes active, essentially turning them into photosynthesising plants. So this is an example of fusion between different creatures, with activation and deactivation of DNA that is dependant on environmental factors. Therefore, what applies to parts of cells living in other cells might well apply to whole organisms living in the bodies of other organisms, just like many protozoa and bacteria live in the digestive tract of members of the animal kingdom (including us). Still sounds like science fiction?
You might not be the only one thinking so. This idea is as controversial as it sounds and it made many developmental biologists scream and run around their labs in utter despair. So, if you would like to find out more about the counter arguments, we recommend you read this article on American Scientist or listen to the "Goo and You" episode of Radiolab, which presents both sides of the story in a compelling way. Furthermore, we couldn't encourage you more to go and yourself grab a copy of Bernd Heinrich's "Life Everlasting", a beautifully written science book which examines this concept in great detail and spellbinding poetry.
And of course, from these captivating ideas and speculations, it is almost impossible not to let the mind wonder to questions such as, what could the caterpillar feel during this process? Does it feel any pain? Does it even have any form of preserved nervous tissue in the process or does it all dissolve into brown goo? As the scans from Manchester University are unable to show brain development, let alone activity, we still have no answers to these questions, and the mystery of the butterfly birth remains as puzzling as ever.
Regardless of the philosophical discussions which we got into at length during those four days and nights, after roughly ninety-six hours the chrysalis started to turn transparent and under the very thin coating you could begin to clearly distinguish the wing patterns, the legs and even the eyes. On the fifth morning, to our surprise and joy, the delicate magnolia butterflies emerged. This emergence is one of the strangest and most hypnotic experiences we have ever had the pleasure of witnessing. The slow strained emergence is reminiscent of a scene out of a science fiction movie, both beautiful and disturbing. As they all emerged within twelve hours of each other we managed to record this short film for you to see, and we'd be curious to know what effect it has on other people. As you can see from the video, after the butterfly breaks free from its old house, it has to inflate its wings, which are still folded and crumpled, not ready for flight. So the butterfly hastily finds a suitable vertical position in order to allow gravity to assist, pumping fluid from its body into the hollow structural framework of the wings. Furthermore, the proboscis at this stage is still made of two separate tubes, which the butterfly needs to fuse together and flex into a single springy spiral, essential for feeding on liquids and rotting fruit. Both tasks require lots of time and patience and took about two hours of intense labour for our butterflies, before they were fit and ready to fly off into their next life.
Complete metamorphosis is a risky and complex business, many don't quite make it to the other side. A couple of caterpillars didn't attach properly to the surface, one fell and died, one didn't even make it to chrysalis stage and of the ones that emerged, one was missing the proboscis, another didn't develop one of its forewings fully. As tragic as this sounds, it is actually fairly normal that many don't make it to the adult, reproductive stage. Furthermore, when you consider that we started off with just under twenty caterpillars, the success rate is still quite high and enough to trouble any herb and vegetable grower.
In about two to three hours after emerging, the butterflies drummed up the courage to take flight into the world, including the one with an underdeveloped wing. At this stage of their life cycle they have just one thing in mind: sex. Hopefully they will mate and go on to lay their wonderful eggs away from what remains of our rocket. It is known that despite their size, they can fly up to 12km a day and some even cross the channel from continental Europe to England. Quite an impressive use of energy, considering that a salad barely fills me for an hour before I need more food!
Nick & Greta, Oropendola Productions