A Buzz in the Meadow (12 page)

Studying the genitalia proved much harder. To measure them the poor butterfly has to be killed, partially dissolved in strong alkali, and then the genitalia pulled out and spread on a slide to look at them under a microscope. Studying them in action was still more challenging. There were umpteen published studies describing the genitalia of male insects of different species, but no one seemed to have looked to see what exactly they did when in contact with the female. Did they really form a key that perfectly matched the female lock? Finding mating butterflies in the field is fairly easy, particularly with common species such as the meadow brown. They can sometimes be seen flying around, the larger female carrying the male dangling behind her, but usually when mating they sit still on a stout grass stem. However, at the slightest disturbance they tend to separate. In any case it is impossible to see what is really going on with the naked eye, as the genitalia are too small. I needed somehow to persuade the mating couple to sit on the stage of a microscope, but that was hardly practical.

After much thought I came up with a cunning plan. I filled a square polystyrene cool-box with liquid nitrogen, strapped it to the rear seat of my bike and rode out to Bernwood. Liquid nitrogen is very cool stuff, in both senses of the word. It boils at -196°C. It can render rubber or metal so cold that they become as fragile as glass – even the most expensive padlock will shatter like a cheap plastic toy if dipped in liquid nitrogen and then given a gentle tap with a hammer. When it is exposed it rapidly boils, releasing super-cool nitrogen gas, which freezes water vapour and carbon dioxide in the surrounding air.

As I banked around the roundabout at the top of the Headington Road, some liquid nitrogen spilled, creating a brief cloud of white vapour behind me, which must have momentarily confused other motorists. But otherwise all went well. Once in the meadow I searched for mating butterflies, carrying the cool-box with me. Before long I spotted a pair, dangling from one of the seedheads of a tussock of cocksfoot grass. I took the lid off the cool-box, placed the container beneath them, then gave the seedhead a firm tap. As I had hoped, the pair tumbled down into the liquid nitrogen and were instantly frozen, still locked together in copulation. I left them there and collected a few more in the same fashion, before returning to the lab at Oxford Brookes.

Back at the university I set up a microscope in one of the walk-in freezer rooms, and there I could examine my frozen couples at leisure. It became clear that only parts of the male valves were actually in contact with the female. To return to my analogy of paired hands, the main area that gripped the female was the lower edge – the little finger and side of the palm. The ‘thumb' was nowhere near contacting the female, so presumably it didn't matter what shape it was. This seemed to explain why this part of the valve was so variable: if it doesn't really do anything, then natural selection would not act upon it, whereas those parts that grip the female would be under strong selective pressure to match precisely the female's shape.

I investigated all of this further with a second experiment in which I tried to measure the strength of the bond between male and female. I wondered if any attributes of the male genitalia – such as size or the shape of the ‘thumb' – might affect the strength of the bond. If I was correct in thinking that the thumb wasn't gripping the female, then there should be no relationship. I thawed out my couples, clipped the female to a stand and then attached successively heavier weights to the male, to see at what point the pair fell apart. Of course it might not have been hugely realistic, since the butterflies were dead and so presumably mating with less enthusiasm than usual, but it was the best I could come up with. It worked and, as predicted, the size or shape of the thumb did not seem to affect the strength of the bond. I never did explain why male meadow browns have more variable genitalia than other butterflies. It would have been good to study how the genitalia of lots of other species fit together when mating, but I didn't have time.

During my PhD I also studied whether spottier butterflies tended to fly more than unspotty butterflies – they did not. I looked to see if spottiness affected how often a butterfly mated, or whether it affected mate choices – it did not. I spent a long time grinding up butterflies and running their enzymes along electrophoretic gels in the lab, to get an indirect measure of how much meadow brown butterflies move about in the landscape. The answer was: quite a lot. I tested how long butterflies could sustain flight at different temperatures, and whether they differed in the lower temperature limit at which they could fly, but it didn't reveal much of great interest – more- or less-spotty butterflies all performed much the same. I heated pupae gently from one side, and found that this produced adults with more and bigger spots on the warmer side. This rather undermined much of the work that I had done on spots, and Ford and Dowdeswell before me, for if they were influenced strongly by the environment, then differences in spottiness between populations could simply be due to microclimatic differences. The whole point of Ford's work was to study genetic change, on the assumption that the visible differences in wing patterns of individual butterflies reflected genetic differences. If they simply reflected whether the caterpillar had happened to pupate in a slightly warmer or cooler spot, then the whole thing was a bit of a waste of time.

I followed this up by doing a little work on whether temperature affected the wing patterns of scarlet tiger moths. Oddly, Ford never seems to have bred scarlet tigers himself, to prove beyond doubt that the different colour forms were genetically controlled, although they are quite easy to breed in captivity. I collected some moths from Cothill and did some simple rearing experiments at different temperatures. I found that storing pupae at slightly elevated temperatures resulted in adults that had lost some spots and resembled Ford's intermediate colour morph. If switches between colour morphs could be brought about by changes in temperature, then all Ford was recording throughout those decades may simply have been evidence that the weather at Cothill varied from year to year. I suspect that Sewall Wright would smile, if he were still alive.

Looking back, it is fair to say that my PhD was not a fabulous success, but fortunately I passed. My supervisor didn't really speak to me at all until I was writing it up at the end of three years, and at the time I slightly resented that he gave me such scant advice, but with hindsight I perhaps learned more than I would otherwise have done by having to think for myself. Coming up with lots of duff ideas and trying them out was frustrating, but I guess it may have helped me work out what good ideas look like. That said, I do try to give my own PhD students rather more help than I received.

When next time you are lucky enough to find yourself in a meadow in high summer, keep an eye out for the meadow brown. They are not glamorous as butterflies go, but they have an understated charm. The decades of intense scientific scrutiny are long forgotten, and they seem content to go quietly and unfussily about their unspectacular business, the tiny black dots on their wings mattering not one jot. It seems remarkable now that they could ever have been the subject of such intense and heated debate.

Butterflies are one of the most beautiful of insect groups, for the wings of many types are stunningly colourful, or tastefully ornate, or subtly but intricately shaded, and all possess a symmetry that is lovely to behold. We know that some patterns seem to provide camouflage, that big spots might frighten predators and that bright colours might please a mate or warn a predator that the butterfly is poisonous, but beyond that we can hardly begin to guess what purposes their beauty serves – if, indeed, it serves any at all.

CHAPTER SEVEN

Paper Wasps and Drifting Bees

5
July
2009
. Run:
37
mins
27
secs. Personal best! I was perhaps helped by a vicious little black spaniel in the hamlet of L'Âge Marenche, which chased me, nipping at my heels for
100
metres or more. People: none. Dogs:
7
. Butterfly species:
18
, including a fabulous Queen of Spain fritillary, with silver spots flashing on her underside as she flew. I also got a distant view of a pair of stone curlews in a fallow field to the north – peculiar boggle-eyed, long-legged birds that prefer running to flying. They are a great rarity, even here.

Karl Marx was right, socialism works, it is just that he had the wrong species.

E. O. Wilson

Between the farmhouse at Chez Nauche and the northern boundary I have planted an apple orchard. I'm not really sure why, but I've always loved orchards. My grandparents on my mother's side had a lovely orchard at the end of their large garden in Norfolk. My grandfather had planted the trees himself as a young man – not the short, stunted trees on dwarfing rootstocks that are always used these days (it makes the fruits easier to pick), but proper trees that had grown ten or more metres high. Picking the fruit was a hazardous business requiring long wooden ladders, and much of it fell to the floor, where it was fought over by my grandfather's free-range chickens and swarms of wasps. It was a lovely place in late summer, alive with the buzz of insects. (Sadly, it is now a housing estate.) Old orchards with full-sized trees are rare these days, and are havens for insect and bird life, so I really wanted one in France, but there was a problem. I couldn't find anyone who sold apple trees on rootstocks that would allow them to grow to full size. In any case I couldn't really afford to buy enough of them for a proper orchard, so I decided to grow my own from pips. I deliberately bought a range of apple varieties and collected the pips from every one I ate. I sowed them in the greenhouses at Southampton University, pretending that they were for an important research project. They grew well, and after a year were big enough to plant out. My dad often came down to France with me and it was he who planted them out in 2004 and 2005. He planted fifty in total: five wonky rows of ten, with a generous spacing of ten metres between each tree. The ground is pretty stony and hard to dig, so he often had to use a pickaxe to make a hole, but he stuck at it stubbornly and got there in the end. Each small tree he protected against rabbits with a green plastic tube just over a metre tall, tied to a wooden stake.

To my father's continuing annoyance, cows break into the meadow from the farm to the south on a regular basis, and invariably make a beeline for the orchard. The stakes seem to make perfect scratching posts for them, but more often than not the weight of the cow leaning against it snaps the stake and pushes the tree over to a precarious angle, so that the orchard needs endless running repairs. My dad seems to have taken this maintenance as a personal battle between himself and his bovine arch-enemies.

Every year since the orchard was planted, when I go down to Chez Nauche for my first spring visit, I rush eagerly to see how the apple trees are coming along. Apples don't self-pollinate, so the pips will all grow into crosses between the variety of apple that I ate and whatever it was that pollinated it. This has made watching the trees grow particularly exciting, as I have little idea what type of apple each tree will one day produce. It was not until 2011 that I got my first blossom, on one of the most northerly trees near the hedge. Some bees must have brought pollen from apples in the village a kilometre or so to the east, for the blossom duly set and by late summer the little tree was carrying dozens of tiny, bright-red crab apples. They looked beautiful, but were toe-curlingly sour. Crab apples are great for jelly and cider, but I do hope some of the trees one day produce apples that I can eat.

For the first couple of years the trees weren't tall enough to poke out of the top of the tube, and I had to peer down to see how they were doing. This, I soon discovered, was a hairy business, because almost every tube contained not just a small apple tree, but also a paper-wasp nest. The tubes seem to provide a perfect, warm and sheltered environment for these wasps, which zoom out of the top of the tube aggressively if disturbed. However, they probably eat any greenfly or other pests on the apples, and don't seem to do any harm, so they are welcome to their tubular homes as far as I am concerned.

I first came across paper wasps in 1995, when teaching on a field course in the south of Spain. Every year for the eleven years that I was at Southampton University we took all of the first-year biology students for a fortnight to a beautiful corner of Andalucia, about eighty kilometres west of Gibraltar, on the Atlantic coast. It was an epic undertaking, for there were usually more than 100 students, but it was great fun and a wonderful way to enthuse them with the excitement of field biology. The area is extraordinarily rich in wildlife. Rugged, craggy mountains cloaked in cork oaks rise steeply from the sandy beaches and coastal dunes, and griffon vultures soar about the steep cliffs. We went in late March, when the wild flowers are in riotous bloom in the rough meadows, rocky slopes and the damper slacks behind the dunes, and they attract innumerable bees, hoverflies and butterflies, such as the spectacular red, black and white Spanish festoon. This is also the time when birds that have migrated to Africa for the winter return to Europe, and many choose to cross here from Morocco, which is clearly visible across the chilly blue-grey Straits of Gibraltar. Storks, black kites and bee-eaters arrive in large flocks, often looking tired and flying low to the water, for there are no thermals to lift them when crossing the sea. The area is also particularly rich in reptiles: turtles bask on the banks of the streams, viperine snakes hunt the tadpoles of toads and tree frogs in the shallows, skinks, geckos and eyed lizards scamper amongst the sun-warmed rocks, and chameleons perch motionless in the bushes.