by Dave Goulson
The obvious thing to do would have been to dredge out the rubble. I cannot recall why I initially decided against this. Instead, I hatched a plan for a much larger replacement pond, which I would create by damming the stream flowing from the small spring in the meadow. I reasoned that I could dig out a substantial lake in the valley below the spring. I envisioned an expanse of wind-ruffled water sparkling in the sunshine and reflecting the clear-blue Charente sky, with fish turning, perhaps the odd heron, and many happy newts frolicking in the shallows.
My initial thought was that I would perhaps get someone with a digger to scoop out the lake, so I asked around among my limited local contacts. I eventually found a chap by the name of Marcel who came to look at the spring and, if I understood him correctly, declared that he could create a fine lake. However, his quote for the work, when it arrived by post a few days later, was for 7,000 euros, which would have made it the world’s most expensive newt home. Plan B was to dig it out by hand. After all, the Suez Canal was dug by hand – how hard could it be to make a small lake? I figured that the spoil heap could be used to create a mighty dam across the valley. And why stop at one lake? I could have a whole series, with the water spilling attractively over a series of weirs from one to the next. In my head, it was a marvellous scheme.
So it was that, on subsequent trips to France, whenever I had a spare moment I would dig. There are always lots of other things to do, making the house more comfortable and looking after the meadow, so the digging wasn’t a top priority and it went slowly. I initially made three dams about fifteen metres apart, each strengthened by several wheelbarrows full of stone rubble carried down from the partially demolished barn. The soil in the valley is heavy clay and full of flints, so it is exceedingly difficult to penetrate with a spade, and when it dries in summer it becomes as hard as concrete. The only way to make any inroad at all was to hack at it with a pickaxe, and then shovel up the loosened soil – blistering and back-breaking work.
By 2008, despairing of ever seeing the mighty expanses of water that lurked only in my imagination, I decided to organise another work party. At this stage I was at Stirling University, and I invited down a group of friends to dig. It might not seem like the most attractive prospect, travelling 1,600 kilometres to dig a hole in the ground, but one should never underestimate the appeal of the offer of unlimited supplies of French cheese and wine. Five of them volunteered, all staff from the university, and so we formed a chain gang, hacking away at the hard earth and taking it in turns to bring more stone down from the barn. We focused our efforts on one lake; the dam slowly rose, and the hole widened. It was September, and the sun shone from a cloudless blue sky, as it tends to do at that time of year. It became hellishly hot in the hole, sheltered as it was from any hint of a breeze. After a week of dusty toil and blistered hands we had a cavity perhaps two metres deep, six metres wide, and nine metres long. It still wasn’t really going to be enough to go boating on, but it was considerably larger than the hollow I had foolishly filled in up near the house. It should certainly be big enough for quite a lot of newts. However, it had been a dry summer and not a drop of rain had fallen during our stay. The trickle of water from the spring petered out before the hole, sinking into the parched soil, so I guessed it would not fill up until the autumn rains set in, as they usually do. We shut up the farm for the winter and returned home.
The following spring, on my next visit, I ran down to inspect the pond. I was sure it would be full, with perhaps a few frogs and newts, water beetles, pond skaters, and so on. As I jogged down the hill I recalled how quickly the pond I had dug as a child in our garden in rural Shropshire had been magically colonised by a host of fascinating aquatic life. Imagine my disappointment to find the hole largely unchanged. There was a tiny puddle in the bottom, perhaps forty-five centimetres across, and one solitary frog, which ineffectually attempted to hide in the few centimetres of water. It had clearly not been a very wet winter, for the meadow grass was shorter than usual, but this was not the cause of the problem. A mole had, quite literally, undermined all our hard work. The lower face of the dam was dotted with molehills, and the steady trickle of water coming down from the spring was pouring straight through the mole tunnels and under the dam. Why the mole should have chosen to dig here, in the bottom of a stony hole in the ground, when there was a whole meadow of softer, worm-rich soil for it to burrow around in was beyond me.
I battled with that mole for the next two years. I puddled clay to a thick, smooth consistency and poured it into his tunnels, hoping that it would dry and set hard. The mole was undeterred and every morning new molehills appeared. I rammed rocks down all of the holes, stamping them in with my feet and sealing around them with more clay, but the mole just popped up elsewhere; every morning two or three more molehills would announce his stubborn resistance to my attempts to drive him away. In desperation I mixed concrete and lined the inside face of the dam with it, but before it could set each evening the mole pushed holes through it, leaving a pile of crumbled cement and newly excavated soil. I began to empathise with the American soldiers in Vietnam, ineffectually trying to flush an unseen enemy from its underground network of tunnels and bunkers. For all my efforts, the hole remained just that, home to a solitary frog and, of course, a mole.
It was not until the spring of 2012 that I finally won this battle. Perhaps the mole simply died of old age and, if so, I imagine that he had a smug, satisfied smile upon his furry pointed face when he went. The weather may have been what turned the tide, for the late winter was exceptionally wet, and the water from the spring flowed as strongly as I have ever seen it, perhaps flooding the mole out of his network of tunnels beneath the dam. The torrent of water had washed mud down, silting up the deepest part of the hole and perhaps blocking up the tunnels, although there were still a few leaks. Whatever the cause, when I visited in May 2012 the pond was full of water, nearly reaching the top of the dam. What was even more exciting, it was alive with creatures. Several frogs leapt from the banks as I approached, plunging into the cool depths. Whirligig beetles gyrated on the water surface, perhaps having flown up from the pools on the meandering Transon nearby. Pond skaters skittered about, disturbed by the frogs, and water boatmen rowed their way jerkily along beneath the surface. Damp-loving ragged robin had appeared from nowhere and was flowering on the bank, offering a perch for dozens of damselflies, including both common red and blue-spots. There were no demoiselles, for they seem to prefer running water. But there was a blue chaser dragonfly perched on a dead thistle stem hanging over the water, a lovely species with a fat blue body with a powdery bloom like a plum, and powerful, fast flight. I couldn’t resist it, and quickly stripped off and jumped into the pond, causing quite a stir amongst the whirligigs. There wasn’t really room for much of a swim, more of a muddy wallow, but it was wonderful until I noticed a lot of coypu faeces floating around me, which slightly took the edge off the experience.
In The Field of Dreams, a strange and rather dull movie about baseball, Kevin Costner is advised that ‘If you build it, they will come.’ I’m not sure this is generally useful advice, particularly if moles are involved (so far as I recall, no moles attempted to thwart Kevin’s efforts in the film, although it might have been more interesting if they had), but it is certainly true of ponds. I would recommend that anyone who has a spare corner of their garden should consider installing one, because there is no doubt that it will soon be teeming with insects and, if you are lucky, with a few amphibians too. It is the one single addition to any garden that will make the biggest difference in encouraging wildlife. Sadly, the only creatures that have not yet arrived at my pond are the newts that motivated its construction, but I live in hope. Every spring I check for them with my boys, using our pond-dipping nets to dredge out any that might be lurking in the depths, but as yet without luck. I am sure that, given time, they will come.
CHAPTER FOUR
Mating Wheels and Sexual Cannibalism
9 May 2008. Run: 39
mins 6 secs. A little faster today – perhaps the marathon training is paying off! People: 2 – a rare sighting of young people in Épenède, a little girl walking to the postbox with her mother. Dogs: 4. Butterfly species: 11, including dainty wood whites fluttering demurely in the shaded lane along the south-west edge of the meadow. I also came across a hedgehog out for an early-morning snuffle, or perhaps on its way home after a busy night of chomping worms. I love their rolling gait, reminiscent of an old man with a gammy hip on the way back from the pub.
Dragonflies are amazing but primitive insects, and I was thrilled to see them occupy the new pond at Chez Nauche. They have not changed much since the Carboniferous, 320 million years ago, when they were the largest animals in the air. Back then, some species were well over sixty centimetres across, the top aerial predators of their day, and they remained kings of the sky for 100 million years until displaced by the pterosaurs. Dragonflies snatch their prey in mid-air, scooping them up with their forward-curved, spiny legs, which form a basket beneath them as they fly. When hunting they can accelerate to well in excess of fifty kilometres per hour, much faster than most of their hapless prey, which includes flies, bees, wasps, butterflies, damselflies and even other dragonflies. Dragonflies have the largest eyes in the insect world, with up to 30,000 facets, and wrapping entirely around their head so that they can see in all directions at once. Close up, their eyes have a multicoloured iridescence, a little reminiscent of the colours on a compact disc, but with a three-dimensional, almost holographic, effect.
There are many fascinating aspects to the biology of dragonflies. They lay their eggs in fresh water, and their nymphs are themselves voracious predators. They are squat and brown, ugly ducklings that show no signs of the beauty that is to come in adulthood. They feed with a mechanism similar to the gruesome alien in the film of the same name; they are ambush predators, waiting motionless until a small fish or tadpole swims near. Then, in the blink of an eye, their telescopic jaws unfold forward from their face and their prey is punctured by their sharp mandibles and drawn back to be consumed. When fully grown, the nymph climbs out of the water, generally using a reed stem, and the adult bursts out from within, leaving behind a papery brown husk.
The adults are quite long-lived by insect standards, some spending several months on the wing, searching for a mate and laying eggs. Their courtship and mating are peculiar even by the standards of the wonderful world of insect sex. The male dragonfly has a pair of claspers at the tip of his long, thin body, which perfectly fit the base of the neck of the female of his species, but will fit no other. Male dragonflies spend much of their time searching for a female, or guarding a resource – a pond – that they know females need to visit to lay their eggs. If they see a female they will attempt to grab her by the neck, either in mid-air or by waiting until she has perched to lay an egg. They will happily grab newly emerging females who are not yet able to fly, or will attack mating couples, attempting to tear them apart and grab the female for themselves. The females usually try to avoid male attentions, and will take evasive action if they have the chance.
Once a male has captured a female, he will not readily let her go. In many species the male’s claspers are armed with spines, which actually stab into the head of the female, making it extremely hard for her to escape or for another male to separate them. Couples may stay locked together for days, flying around in tandem, with the male in front, the female being towed behind by the scruff of the neck. It may sound undignified, but they look rather beautiful together.
Before they can actually mate, there are various logistical problems that they must overcome, and that require the cooperation of both parties. First, the male’s testes are positioned near the tip of his body, which is now behind the female’s head. Unusually, his penis is tucked up near the front of his abdomen, just behind the wings. If he has any sense, he will have carefully transferred a packet of sperm from the testes to the base of the penis by bending his abdomen double before he grasped hold of the female. If he did not, he is wasting his time. For them to mate, the female has to curve her own abdomen forward and underneath her head, so that her genitalia at the tip come into contact with the male’s penis. At this point the couple’s bodies form a rough circle or, more precisely, a rather romantic, lopsided heart shape, sometimes known as a mating wheel. Once her reproductive parts are in place, the male uses his penis to scrape out the receptacle in which the female stores sperm, in an attempt to remove all the sperm from any previous suitor. To this end, male dragonflies have penises that, in different species, variously resemble ice-cream scoops or scrubbing brushes. Once this sticky job is complete, the male transfers his own parcel of sperm. Having done so, he hangs on to the female for as long as he can. If he lets go, she is sure to be grabbed by another male and his sperm will then be unceremoniously removed, so if he wishes to have offspring he must hang on until she uses his sperm to fertilise her eggs. So it happens that, for much of the summer, most adult dragonflies are in pairs. They will hunt, sleep and she will lay eggs while locked together. Once she has laid eggs, he can be fairly sure that he has fathered at least some of the offspring.
You may wonder why the female would be willing to mate after being grabbed by a male without courtship, and after trying to evade him and reject his advances. The answer is presumably that she has to mate with someone. Having done her best to escape, she has established that this particular male must be fairly fast and strong, and so hopefully her sons will inherit his vigour.
There is something of a puzzle as to why dragonflies have evolved such a bizarre and complex way of mating. The explanation may be that it came about as a means of avoiding being eaten by their intended mate. In most mammals, males tend to be bigger and stronger than females; they need to be able to fight for access to females. Hence male red deer, the stags, are much more powerful and have much larger antlers than the females. In contrast, in insects it is generally the females that are larger; the bigger the female, the more eggs she can produce, whereas in males high mobility (to find mates) is usually more important than size. Hence natural selection has favoured voluptuous females and skinny, nippy males.1 As a result, sex in many predatory insects and also spiders is fraught with danger for the male of the species, for the females are often the larger and more powerful sex. Male dragonflies have largely overcome this problem by swooping on the object of their desire from above and behind; once he has firmly grasped her by the neck, he is safe from her powerful legs and jaws.
Male mantises have not yet come up with an entirely adequate solution to this problem. It may be that mantises evolved relatively more recently, about 100 million years ago, and so have had less time to come up with an answer than the dragonflies. The female mantis is considerably bigger and stronger than the male, so she is readily able to overpower and eat him, should she prefer a snack to sex. For the amorous male, gauging the mood of his potential mate as accurately as possible could not be more important; it is a matter of life or death.
It has long been known that female mantises commonly eat their mate during the act of copulation – the famous French entomologist Jean-Henri Fabre described this in the 1800s. Some have argued that it is an essential part of mating. Indeed, once the male’s head has been removed – this is usually the first body part that the female consumes – his mating seems to become more enthusiastic, his body pumping vigorously. Of course his body might as well give it everything at this point, as it isn’t going anywhere afterwards. Indeed, the male often doesn’t get as far as copulating before he loses his head. Bizarrely, the male can still successfully initiate copulation after his head had been removed. In a series of odd experiments carried out by K.D. Roeder of Tufts University, Massachusetts, in the 1930s he demonstrated that successful mating can in fact take place when neither partner has a head, though perhaps this is of little relevance to what happens in nature.
It has been suggested that it may be in the male’s interests to be consumed during copulation
, for he is providing a large meal to his partner that may enable her to produce more of his offspring. However, this is only likely to be so if his chances of finding another female and mating again are slim; otherwise he is giving up all chance of mating again for the benefit of providing one meal to his current partner. Males of most animals are not so self-sacrificing.2
Some years ago I had the chance to study this for myself. I had gone on a cheap package holiday with my wife to Gambia, a country with an immense diversity of wildlife. The area around our hotel was almost dripping with mantises of various species, and their large egg masses, known as oothecae, were stuck all over various ornamental shrubs and could even be found on the walls of the hotel. I’d always been intrigued by the mating habits of mantises, and this seemed like an ideal opportunity to get hold of enough to do some experiments. I brought some oothecae back with me, and in the dingy basement of the biology building at the University of Southampton I set about rearing them.
Many of the oothecae produced only tiny parasitic wasps, the females armed with enormous ovipositors far longer than their bodies. These they clearly use to stab into fresh oothecae, laying their eggs deep inside, where they hatch and consume the eggs of the mantis. I pickled them in alcohol, and to this day have not got round to checking whether they belong to a species known to science. Fortunately some oothecae had escaped the depredations of the wasps, and dozens of tiny mantis nymphs emerged from these. Rearing mantises is problematic, as they are enthusiastic cannibals from day one. If they are housed together, a group of a dozen small mantises quickly becomes one bigger mantis, so they each have to be housed and fed individually, on fruit flies to start with, moving on to house flies and then small crickets. Luckily one of our technical staff, a shambling bear of a man called Keith, absolutely loved mantises and gave me heaps of help. Eventually, after an awful lot of work, we had several hundred splendid adult mantises, each about ten centimetres long. We kept them for another week or so to make sure they were mature, and then I began my experiments.
