THE BOTANICAL INSTINCT
Maternity, when it takes thought for the future, is the most fertile
prompter of instinct. To the maternity that prepares board and lodging
for the family we owe the wonderful achievements of the Dung-beetles
and of the Wasps and Bees. The moment the mother confines herself to
laying eggs and becomes a mere germ-factory, the industrial talents
disappear as useless.
That bravely-plumed fine lady, the Pine Cockchafer, digs the sandy soil
with the tip of her abdomen and buries herself in it laboriously right
up to her head. Then a bundle of eggs is laid at the bottom of the
excavation; and that is all, once the pit has been filled by means of a
casual sweeping.
Constantly ridden by her male during the four weeks of July, the mother
Capricorn explores the trunk of the oak at random; she slips her
retractable oviscapt, here, there and everywhere, under the scales of
the cracked bark, probing, feeling, choosing the propitious spots. Each
time an egg is laid, almost without protection. This done, she has no
further anxiety.
The grub of Cetonia floricola, breaking its shell, some time in August,
in the depths of the leaf-mould, goes to feed on the flowers and there
idly slumbers; then, an adult Rose-chafer, she returns to the heap of
rotten leaves, enters it and sows her eggs in the hottest places, those
where fermentation rages most fiercely. Let us not ask anything further
from her: her talents end with this.
So it is, in the vast majority of cases, with the other insects, weak
or powerful, lowly or splendid. They all know where the eggs must be
established, but they are profoundly indifferent to what will follow.
It is for the grub to muddle through by its own methods. The Pine
Cockchafer’s larva dives farther into the sand, seeking for tender
rootlets softened by incipient decay. The Capricorn’s, continuing to
drag the shell of its egg behind it, nibbles the uneatable for its
first mouthful, making flour of the dead bark and sinking a shaft that
leads it to the wood, on which it feeds for the next three years. The
Cetonia’s, born in a heap of decomposed vegetable matter, has its food
ready to its mouth, without seeking.
With such primitive habits as these, which emancipate the family at
birth, without the least previous training, how far removed are we from
the maternal tenderness of the Copris, [31] the Necrophorus, [32] the
Sphex [33] and so many others! Apart from these privileged tribes,
there is nothing very striking to be noted. It is enough to fill with
despair the observer in search of facts really worth recording.
The children, it is true, often make up to us for their untalented
mothers. Their ingenuity is sometimes amazing, from the time when they
are hatched. Witness our Larini. What can the mother do? Nothing but
bury the eggs in the blossoms of the thistles. But what a singular
industry on the part of the grub which builds itself a thatched hut,
upholsters itself a cabin, cards itself a mattress of chopped hairs,
makes itself a defensive pitcher, a donjon-keep, with the shellac
prepared by its intestine!
When the transformation is accomplished, what perspicacity on the part
of the inexperienced insect, when it abandons its cosy home to seek a
refuge under the rude shelter of the stones, foreseeing the winter
which will ruin the natal villa! We possess the almanac of the past,
telling us of the almanac of the future. The insect, with no records of
the vicissitudes of the seasons; the insect, born in the dog-days, in
the blazing heat of summer: the insect feels instinctively that this
period of solar intoxication will not last; it knows, though it has
never seen it happen, that its house is doomed soon to collapse; and it
makes off before the roof falls in.
For a Weevil, this is fine, magnificent. We might well envy the
creature’s wisdom in being thus awake to the calamities of the future.
However devoid of industry she may be, the least-gifted mother none the
less submits an insoluble problem for our consideration. What is it
that leads her to lay her eggs at spots where the larvæ will find food
to their liking?
The Pieris [34] goes to the cabbage, in which she has no personal
interest. The plant, compressed into a head, has not yet flowered.
Besides, its modest yellow blossoms have no greater attraction for the
Butterfly than an infinity of other flowers distributed broadcast. The
Vanessa [35] goes to the nettle, on which her caterpillars will feast,
but on which the adult insect finds nothing to suck.
When, in the summer gloaming, the Pine Cockchafer has long been
whirling in the nuptial ballet around her favourite tree, she refreshes
herself after her fatigue by nibbling a few pine-needles; then, with
impetuous flight, she goes in search of some bare, sandy tract where
the grass-roots lie decaying. Here, as often as not, there is no
resinous aroma, there are no more pine-trees, the delight of the plumed
beauty; and it is in this place, where nothing appeals to her own
needs, that the mother, half-buried in the ground, will lay her egg.
That ardent lover of roses and hawthorn-blossom, the Golden Cetonia,
leaves the luxury of the flowers, to burrow in the shame of
putrescence. She repairs to the compost-heap, but is certainly not
tempted by any dish to her taste. She cannot sip honey there nor
intoxicate herself with perfumed essences. Another reason draws her to
this corruption.
At first sight it would seem as if these strange instincts might be
explained by the larva’s diet, of which the adult would retain a lively
recollection. The caterpillar of the Pieris fed on cabbage-leaves; the
caterpillar of the Vanessa fed on nettle-leaves; and each of the two
Butterflies, endowed with a faithful memory, exploits the plant which
has no attraction for her now, but which was a treat for her in her
infancy.
In the same way, the Cetonia dives into the heap of leaf-mould because
she remembers the feasts of former days, when she was a grub in the
midst of the fermenting vegetable matter; and the Pine Cockchafer seeks
the sandy tracts covered with lean tufts of grass, because she
remembers her youthful revels underground amid the decaying rootlets.
Such a memory would be almost admissible if the adult’s diet were the
same as the larva’s. We can more or less understand the Dung-beetle,
who, herself feeding upon animal droppings, makes them into canned
provisions for her family. The diet of maturity and that of infancy are
linked as though each were a reminiscence of the other. Uniformity
offers a very simple solution of the food-problem.
But what shall we say of the Cetonia passing from the flowers to the
sordid refuse of the decayed leaves? Above all, what shall we say of
the Hunting Wasps? These fill their own crops with honey and feed their
youngsters on prey!
By what inconceivable inspiration does the Cerceris [36] leave the
refreshment-bar of the blossoms, dripping with nectar, to go a-hunting
and to slay the Weevil, the game destined for her offspring? How are we
to explain the Sphex, who, having refreshed herself at the sugar-works
of the field eringo, suddenly flies off, eager to stab the Cricket, the
food of her grub?
It is a matter of memory, some will make haste to reply.
Ah no! Please do not speak of memory here; do not appeal to the belly’s
powers of reminiscence! Man is fairly well endowed with mnemonic
aptitudes. Yet which of us has retained the least recollection of his
mother’s milk? If we had never seen a babe at the breast, we could
never suspect that we began life in the same fashion.
This food of earliest infancy is not remembered; it is certified only
by example, as by that of the Lamb, which, with bended knees and
frisking tail, sucks at the udder and butts it with its head. No, the
mouthfuls of mother’s milk have left not a trace in the mind.
And you would have it that the insect, after a transformation that has
changed it entirely, both inside and out, remembers its first diet,
when we ourselves, who are not remoulded in the crucible of a
metamorphosis, remain in the most absolute darkness where ours is
concerned! My credulity will not go to that length.
How then does the mother, whose diet is different, distinguish what
suits her offspring? I do not know, I never shall know. It is an
inviolable secret. The mother herself does not know. What does the
stomach know of its masterly chemistry? Nothing. What does the heart
know of its wonderful hydraulics? Nothing. The pregnant mother, when
establishing her brood, knows no more.
And this unconsciousness provides us with an admirable solution of the
difficult problem of victuals. A good example is afforded by the
Weevils whom we have just been considering. They will show us with what
botanical tact the choice of the food-plant is made.
To entrust the batch of eggs to this or that cluster of florets is not
a matter of indifference. It is indispensable that the florets should
fulfil certain conditions of flavour, stability, hairiness, and other
qualities appreciated by the grub. Its selection, therefore, demands a
nice botanical discrimination which will recognize off-hand the good
and the bad, accept the discovery or reject it. Let us devote a few
lines to these Weevils from the point of view of their botanical
attainments.
Scorning variety, the Spotted Larinus is a specialist of immovable
convictions. Her domain is the blue ball of the echinops, an exclusive
domain, valueless to the others. She alone appreciates it, she alone
exploits it; and nothing else suits her.
This particularity, an unchangeable family inheritance, must greatly
facilitate her search. When, on the return of the warm weather, the
insect leaves her hiding-place, which is doubtless not far from the
spot where she was born, she easily finds, on the banks by the
road-side, her favourite plant, which is already tipping its branches
with pale-blue globes. The dear heritage is recognized without
hesitation. She climbs into it, rejoices in her nuptial diversions and
waits for the azure balls to mature to the requisite stage. The blue
thistle is familiar to her though she sees it for the first time. It
was the only one known in the past; it is the only one known in the
present. There is no confusion possible.
The second Larinus, the Bear, begins to vary her flora to some extent.
I know that she has two establishments: the corymbed carlina in the
plain and the acanthus-leaved carlina on the slopes of Mont Ventoux.
[37]
To those who stop at the general aspect and do not have recourse to
delicate floral analyses, the two plants have nothing in common. The
countryman, clever though he be at distinguishing one plant from
another, would never think of calling the two by the same generic name.
As for the civilized townsman, unless he be a botanist, don’t speak of
him: his testimony here would be worse than useless.
The corymbed carlina has a tall, slender stem; thin, sparse leaves; a
bunch of average flowers, with a receptacle less than half the size of
an acorn. The acanthus-leaved carlina spreads, level with the soil, a
large, fierce rosette of broad leaves which in shape is not unlike the
ornament of a Corinthian capital. There is no stem. In the centre of
the leaf-cluster is a flower, one only, but a giant, big as a man’s
fist.
The people of Mont Ventoux call this magnificent thistle the ‘mountain
artichoke.’ They gather it and use the base of the flower in making
omelettes not devoid of merit; this base is very fleshy, is saturated
in milk with a nutty flavour and is delicious even when raw.
Sometimes they use the plant as an hygrometer. Nailed to the lintel of
the byre, the carlina closes its flower when the air is moist and opens
it in a superb sun of golden scales when the air is dry. With beauty
added, it is the inverse equivalent of the celebrated rose of Jericho,
an unsightly bundle which expands in wet and shrivels in dry weather.
If the rustic hygrometer were a foreigner, it would be famous; being an
ordinary product of Mont Ventoux, it is slighted.
The Larinus, for her part, knows it very well, not as a meteorological
apparatus, a very useless thing to her for foretelling the weather, but
as provender for her family. Many a time, on my excursions in July and
August, I have seen the Bear Weevil very busy on the mountain artichoke
wide open in the sun. There is no doubt what she was doing there: she
was attending to her eggs.
I regret that my then preoccupations, which were concerned with botany,
did not permit me to observe the mother’s methods more closely. Does
she lay several eggs in this rich morsel? There is enough to satisfy a
numerous brood. Or does she lay only one, repeating here what she does
on the corymbed carlina, a middling ration? There is nothing to tell us
that the insect is not to some extent versed in domestic economy and
does not proportion the number of the guests to the abundance of the
provisions.
If this point is obscure, another and one of greater interest is quite
evident: the Bear Larinus is a clear-sighted botanist. She recognizes
as carlina, the family food, two very dissimilar plants, which none of
us, unless he were an expert, would have thought of grouping together;
she accepts as botanical equivalents the gorgeous rosette, eighteen
inches across, whose spokes lie on the ground, and the shabby-looking
thistle that stands erect and spare.
The Spangled Larinus extends her domain still farther. Though she has
not the fierce thistle with the white heads, she recognizes the good
qualities of another vegetable horror, one with pink heads this time.
This is the common horse-thistle (Cirsium lanceolatum, Scop.). The
difference in the colour of the flowers causes her no hesitation.
Can she be apprised by the majestic stature, by the sturdy prickles?
No, for we next see her established on a humble and much less savage
plant, Carduus nigrescens, Vill., which rises hardly more than nine
inches from the ground.
Can it be the size of the heads that regulates her choice? Not so,
either, for the paltry heads of Carduus tenuiflorus, Cart., are
accepted as readily as the sizable blooms of the above three thistles.
But the subtle expert is even cleverer than this. Regardless of mien,
foliage, flavour or colour, she actively exploits Kentrophyllum
lanatum, D. C., a plant with wretched yellow flowers soiled by the dust
of the roads. To recognize a Carduacea in this dry and unsightly plant
you have to be a botanist or a Weevil.
A fourth Larinus (L. scolymi, Oliv.) surpasses the Spangled Larinus. We
find her at work on the garden artichoke and the garden cardoon, both
of them giants that lift their great blue heads to a height of six feet
and more. We meet her afterwards on a niggardly centaury (Centaurea
aspera, Lin.), with ragged heads, smaller than the tip of one’s little
finger, trailing on the ground; we see her founding colonies on the
various thistles beloved of the Spangled Larinus, even on Kentrophyllum
lanatum. Her botanical knowledge of plants so dissimilar gives us food
for reflection.
As a Weevil, she recognizes very clearly, without resorting to tests,
what is artichoke-heart and what is not, what suits her offspring and
what would harm it; and I, as a naturalist, versed by assiduous
practice in the flora of my district, would not dare, without prudent
inquiries, to bite into this or that fruit or berry were I suddenly
transported to another country.
She is born with her knowledge; and I have to learn. Every summer, with
superb audacity, she goes from her thistle to various others which,
having no similarity of appearance, ought, one would think, to be
rejected as suspicious hostelries. On the contrary, she accepts them,
recognizes them as her own; and her confidence is never betrayed.
Her guide is instinct, which instructs her unerringly, within a very
restricted circle; mine is intelligence, which gropes, seeks, goes
astray, finds its way again and ends by soaring with an incomparable
flight. The Larinus knows the flora of the thistles without having
learnt it; man knows the flora of the world after long study. The
domain of instinct is a speck; that of intelligence is the universe.