THE EMIGRANTS

Insect life: Souvenirs of a naturalist by Jean-Henri Fabre, is part of the HackerNoon Books Series. You can jump to any chapter in this book here. THE EMIGRANTS

XIV. THE EMIGRANTS

I have already told how on the top of Mont Ventoux, some 6000 feet above the sea, I had one of those pieces of entomological good luck, which would be fruitful indeed did they but occur often enough to allow of continuous study. Unhappily mine is a unique observation, and I despair of repeating it. Future observers must replace my probabilities by certainties. I can only found conjectures on it.Under the shelter of a large flat stone I discovered some hundreds of Ammophila hirsuta, heaped in a mass almost as compact as a swarm of bees. As soon as the stone was lifted all the small people began to move about, but without any attempt to take wing. I moved whole handfuls, but not one seemed inclined to leave the heap. Common interests appeared to unite them indissolubly. Not one would go unless all went. With all possible care I examined the flat stone which sheltered them, as well as the soil and immediate neighbourhood, but could discover no explanation of this strange assemblage. Finding nothing better to do, I tried to count them, and then came the clouds to end my observations and plunge us into that perplexing darkness I have already described. At the first drops of rain I hastened to put back the stone and replace the Ammophila people under shelter. I give myself a good mark, as I hope the reader also will, for having taken the precaution of not leaving the poor things, disturbed by my curiosity, exposed to the downpour.AMMOPHILA HIRSUTA ATTACKING A GRUBAmmophila hirsuta is not rare in the plain, but is always found singly on the edge of a road or on sandy slopes, now digging a well, now dragging a heavy prey. It is solitary, like Sphex occitanica, and I was greatly surprised by finding such a number gathered under one stone at the top of Mont Ventoux. Instead of my solitary acquaintance, here was a great assembly. Let us try to educe the probable causes of this agglomeration. By an exception very rare among mining Hymenoptera, Ammophila hirsuta builds in the first days of spring. Toward the end of March, if the season be mild, or at least in the first fortnight of April, when the grasshoppers take their adult form, and painfully cast off their first skin on their thresholds,—when Narcissus poeticus expands its first flowers, and the bunting utters its long-drawn note from the top of the poplars in the meadow,—Ammophila hirsuta sets to work to hollow and provision a home for her larvæ, whereas other species and the predatory Hymenoptera in general undertake this labour only in autumn, during September and October. This very early nidification, preceding by six months the date adopted by the immense majority, at once suggests []certain considerations. One asks if those found burrowing so early in April are really insects of that year—i.e. whether these spring workers completed their metamorphosis and came out of their cocoons during the preceding three months. The general rule is that the Fossor becomes a perfect insect, leaves its burrow, and occupies itself with its larvæ all in one season. It is in June and July that the greater part of the hunting Hymenoptera come from the galleries where they lived as larvæ, and in August, September, and October they follow their occupations as burrowers and hunters.Does a similar law apply to Ammophila hirsuta? Does the same season witness the final transformation and the labours of the insect? It is very doubtful, for the Hymenoptera, occupied with mining at the end of March, would have to complete their metamorphosis and break forth from the cocoon in winter, or at latest in February. The severity of the climate at that date forbids any such conclusion. It is not when the bitter Mistral howls for a fortnight at a time and freezes the ground, nor when snow-storms follow its icy breath, that the delicate transformations of the nymph state can take place, and the perfect insect venture to quit the shelter of its cocoon. It needs the soft dampness of earth under a summer sun before it can leave its cell.If I did but know the exact date at which Ammophila hirsuta leaves the cocoon it would greatly help me; but, to my deep regret, I do not. My notes, gathered day by day, show the confusion inseparable from researches that are generally dealing with points that cannot be foreseen, and are []silent on this point, whose importance I fully realise now that I want to arrange my materials in order to write these lines. I find mention of the Ammophila of the sands coming out of the egg on June 5, and A. argentata on the 20th; but I have nothing in my archives regarding the hatching of A. hirsuta. It is a detail left unnoticed through forgetfulness. The dates for the two other species accord with the general law, the perfect insect appearing at the hot time of year. By analogy I fix the same date for the coming forth of A. hirsuta from the cocoon.Whence, then, come those which one sees at work on their burrows at the end of March and April? We must conclude that they were hatched in the previous year and emerged from their cells at the usual time in June and July, lived through the winter, and began to build as soon as spring came. In a word, they are insects that hibernate. Experience fully confirms this conclusion.Do but search patiently in a vertical bank of earth or sand well exposed to the sun, especially where generations of the various honey-gathering Hymenoptera have followed one another year after year, riddling the ground with a labyrinth of passages till it looks like a huge sponge, you are nearly sure to see in the heart of winter A. hirsuta either alone or in little parties of three or four, crouched in some warm retreat, waiting inactive till summer shall come. This cheering little meeting, amid the gloom and cold of winter, with the graceful insect which at the first notes of the bunting and the cricket enlivens the grassy paths, is one that I have been able to enjoy at will. If the weather be calm and the sun []has a little power, the chilly insect comes out to bask on its threshold, luxuriating in the hottest beams, or it will venture timidly outside and walk slowly over the spongy bank, brushing its wings. So, too, does the little gray lizard, when the sun begins to warm the old wall which is its home.But vainly would one seek in winter, even in the most sheltered spots, for a Cerceris, Sphex, Philanthus, Bembex, and other Hymenoptera with carnivorous larvæ. All died after their autumn labours, and their race is only represented by the larvæ benumbed down in their cells. Thus, by a very rare exception, Ammophila hirsuta, hatched in the hot season, passes the following winter in some warm refuge, and this is why it appears so early in the year.With these data let us try to explain the Ammophila swarm on the crest of Mont Ventoux. What could these numerous Hymenoptera under their sheltering stone have been about? Were they meaning to take up winter quarters there and await under their flat stone, benumbed, the season propitious to their labours? Everything points to the improbability of this. It is not in August, at the time of the greatest heat, that an animal is overcome with winter sleep. Want of their food—the honey juice sucked from flowers—cannot be suggested. September showers will soon come, and vegetation, suspended for a while by the heat of the dog days, will assume new vigour and cover the fields with a flowery carpet almost as varied as that of spring. This period—one of enjoyment for most of the Hymenoptera—cannot possibly be one of torpor for A. hirsuta. Again, can one suppose that the heights []of Ventoux, swept by the gusty Mistral, uprooting beech and pine,—summits where the bise whirls about the snow for six months of the year,—crests wrapped for the greater part of the year by cold clouds and mist,—can be adopted as a winter refuge by such a sun-loving insect? One might as well make it hibernate among the ice fields of the North Cape! No, it is not there that A. hirsuta must pass the cold season. The group observed there were making a temporary halt. At the first indication of rain, which, though it escaped us, could not escape the insect so eminently sensitive to the variations of the atmosphere, the wayfarers had taken refuge under a stone, and were waiting for the rain to pass before they resumed their flight. Whence came they? Where were they going?In this same month of August, and especially in September, there come to the warm olive region flocks of little migratory birds; descending by stages from the lands where they have loved,—fresher, more wooded, more peaceful lands than ours,—where they have brought up their broods. They come almost to a day in an invariable order, as if guided by the dates of an almanac known only to themselves. They sojourn for a while in our plains, where abound the insects which are the chief food of most of them; they visit every clod in our fields where the ploughshare has turned up innumerable worms in the furrows, and feast on them, and with this diet they speedily lay on fat,—a storehouse and reserve to serve as nutrition against toils to come, and thus well provided for the journey they go on southward, to reach winterless []lands where insects are always to be found, such as Spain and Southern Italy, the isles of the Mediterranean and Africa. This is the season for the pleasure of shooting and for succulent roasts of small birds.The Calandrelle, or Crèou, as Provence calls it, is the first to arrive. As soon as August has begun it may be seen exploring the stony fields, seeking the seeds of the Setaria, an ill weed affecting cultivated ground. At the least alarm it flies off, making a harsh guttural sound sufficiently expressed by its Provençal name. It is soon followed by the whinchat, which preys quietly on small weevils, crickets, and ants in old fields of luzern. With the whinchat begins the long line of small birds suitable for the spit. It is continued in September by the most celebrated of them—the common wheat-ear, glorified by all who are capable of appreciating its high qualities. Never did the Beccafico of the Roman gourmet, immortalised in Martial’s epigrams, rival the delicious, perfumed ball of fat the wheat-ear makes when it has grown scandalously obese on an immoderate diet. It consumes every kind of insect voraciously. My archives as a sportsman-naturalist give a list of the contents of its gizzard. All the small people of the fallows are in it,—larvæ and weevils of every kind, crickets, chrysomelides, grasshoppers, cassidides, earwigs, ants, spiders, hundred-legs, snails, wire-worms, and ever so many more. And as a change from this spicy diet there are grapes, blackberries, and cornel-berries. Such is the bill of fare sought incessantly by the wheat-ear as it flutters from clod to clod, the white feathers of its []outspread tail giving it the look of a butterfly on the wing. Heaven only knows to what amount of fat it can attain.Only one other bird surpasses it in the art of fattening itself, and that is its fellow emigrant,—another voracious devourer of insects,—the bush pipit as it is absurdly styled by those who name birds, while the dullest of our shepherds never hesitate to call it Le Grasset, i.e. the fattest of the fat. The name is sufficient to point out its leading characteristic. Never another bird attains such a degree of obesity. A moment arrives when, loaded all over with fat, it becomes like a small pat of butter. The unfortunate bird can hardly flutter from one mulberry tree to another, panting in the thick foliage, half choked with melting fat, a victim to his love of weevil.October brings the slender gray wagtail, pied ash colour and white, with a large black velvet gorget. The charming bird, running and wagging its tail, follows the ploughman almost under the horses’ feet, picking up insects in the newly turned furrow. About the same time comes the lark,—first in little companies thrown out as scouts, then in countless bands which take possession of cornfield and fallow, where abounds their usual food, the seeds of the Setaria. Then on the plain, amid the sparkle of dewdrops and frost crystals suspended to each blade of grass, a mirror shoots intermittent flashes under the morning sun. Then the little owl, driven from shelter by the sportsman, makes its short flight, alights, stands upright with sudden starts and rolling of alarmed eyes, and the lark comes with a dipping []flight, anxious for a close inspection of the bright thing or the odd bird. There it is, some fifteen paces away—its feet hanging, its wings outspread like a saint-esprit. The moment has come; aim and fire. I hope that my readers may experience the emotions of this delightful sport.With the lark, and often in the same flocks, comes the titlark—the sisi—another word giving the bird’s little call. None rushes more vehemently upon the owl, round and round which it circles and hovers incessantly. This may suffice as a review of the birds which visit us. Most of them make it only a halting-place, staying for a few weeks, attracted by the abundance of food, especially of insects; then, strengthened and plump, off they go. A few take up winter quarters in our plains, where snow is very rare, and there are countless little seeds to be picked up even in the heart of the cold season. The lark which searches wheat fields and fallows is one; another is the titlark, which prefers fields of luzern and meadows.The skylark, so common in almost every part of France, does not nest in the plains of Vaucluse, where it is replaced by the crested lark—friend of the highway and of the road-mender. But it is not necessary to go far north to find the favourite places for its broods; the next department, the Drôme, is rich in its nests. Very probably, therefore, among the flocks of larks which take possession of our plains for all autumn and winter many come from no farther than the Drôme. They need only migrate into the next department to find plains that know not snow, and a certainty of little seeds.[]A like migration to a short distance seems to me to have caused the assemblage of Ammophila on the top of Mont Ventoux. I have proved that this insect spends the winter in the perfect state, sheltering somewhere and awaiting April to build its nest. Like the lark it must take precautions against the cold season; though capable of fasting till flowers return, the chilly thing must find protection against the deadly attacks of the cold. It must flee snowy districts, where the soil is deeply frozen, and, gathering in troops like migrant birds, cross hill and dale to seek a home in old walls and banks warmed by a southern sun. When the cold is gone, all or part of the band will return whence they came. This would explain the assemblage on Mont Ventoux. It was a migrant tribe, which, on its way from the cold land of the Drôme to descend into the warm plains of the olive, had to cross the deep, wide valley of the Toulourenc, and, surprised by the rain, halted on the mountain top. Apparently A. hirsuta has to migrate to escape winter cold. When the small migratory birds set out in flocks, it too must journey from a cold district to a neighbouring one which is warmer. Some valleys crossed, some mountains overpassed, and it finds the climate sought.I have two other instances of extraordinary insect gatherings at great heights. I have seen the chapel on Mont Ventoux covered with seven-spotted ladybirds, as they are popularly called. These insects clung to the stone of walls and pavement so close together that the rude building looked, at a few paces off, like an object made of coral beads. I should not dare to say how many myriads were []assembled there. Certainly it was not food which had attracted these eaters of Aphidæ to the top of Mont Ventoux, some 6000 feet high. Vegetation is too scanty—never Aphis ventured up there.Another time, in June, on the tableland of St. Amand, at a height of 734 mètres, I saw a similar gathering, only less numerous. At the most projecting part of the tableland, on the edge of an escarpment of perpendicular rocks, rises a cross with a pedestal of hewn stone. On every side of this pedestal, and on the rocks serving as its base, the very same beetle, the seven-spotted ladybird of Mont Ventoux, was gathered in legions. They were mostly quite still, but wherever the sunbeams struck there was a continuous exchange of place between the newcomers, who wanted to find room, and those resting, who took wing only to return after a short flight. Neither here any more than on the top of Mont Ventoux was there anything to explain the cause of these strange assemblages on arid spots without Aphidæ and noways attractive to Coccinellidæ,—nothing which could suggest the secret of these populous gatherings upon masonry standing at so great an elevation.Have we here two examples of insect migration? Can there be a general meeting such as swallows hold before the day of their common departure? Were these rendezvous whence the cloud of ladybirds were to seek some district richer in food? It may be so, but it is very extraordinary. The ladybird has never been talked of for her love of travel. She seems a home-loving creature enough when we see her slaying the green-fly on rose trees, []and black-fly on beans, and yet with her short wings she mounts to the top of Ventoux and holds a general assembly where the swallow herself only ascends in her wildest flights. Why these gatherings at such heights? Why this liking for blocks of masonry?

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