THE LEUCOPSES





(This chapter should be read in conjunction with the essays entitled

"The Anthrax" and "Larval Dimorphism", forming chapters 2 and 4 of

"The Life of the Fly."--Translator's Note.)



Let us visit the nests of Chalicodoma muraria in July, detaching them

from their pebbles with a sideward blow, as I explained when telling

the story of the Anthrax. The Mason-bee's cocoons with two

inhabitants, one devouring, the other in process of being devoured,

are numerous enough to allow me to gather some dozens in the course of

a morning, before the sun becomes unbearably hot. We will give a smart

tap to the flints so as to loosen the clay domes, wrap these up in

newspapers, fill our box and go home as fast as we can, for the air

will soon be as fiery as the devil's kitchen.



Inspection, which is easier in the shade indoors, soon tells us that,

though the devoured is always the wretched Mason-bee, the devourer

belongs to two different species. In the one case, the cylindrical

form, the creamy-white colouring and the little nipple constituting

the head reveal to us the larva of the Anthrax, which does not concern

us at present; in the other, the general structure and appearance

betray the grub of some Hymenopteron. The Mason's second exterminator

is, in fact, a Leucopsis (Leucopsis gigas, FAB.), a magnificent

insect, stripped black and yellow, with an abdomen rounded at the end

and hollowed out, as is also the back, into a groove to contain a long

rapier, as slender as a horsehair, which the creature unsheathes and

drives through the mortar right into the cell where it proposes to

establish its egg. Before occupying ourselves with its capacities as

an inoculator, let us learn how its larva lives in the invaded cell.



It is a hairless, legless, sightless grub, easily confused, by

inexperienced eyes, with those of various honey-gathering Hymenoptera.

Its more apparent characteristics consist of a colouring like that of

rancid butter, a shiny and as it were oily skin and a segmentation

accentuated by a series of marked swellings, so that, when looked at

from the side, the back is very plainly indented. When at rest, the

larva is like a bow bending round at one point. It is made up of

thirteen segments, including the head. This head, which is very small

compared with the rest of the body, displays no mouth-part under the

lens; at most you see a faint red streak, which calls for the

microscope. You then distinguish two delicate mandibles, very short

and fashioned into a sharp point. A small round mouth, with a fine

piercer on the right and left, is all that the powerful instrument

reveals. As for my best single magnifying-glasses, they show me

nothing at all. On the other hand, we can quite easily, without arming

the eye with a lens, perceive the mouth-apparatus--and particularly

the mandibles--of either a honey-eater, such as an Osmia, Chalicodoma

or Megachile, or a game-eater, such as a Scolia, Ammophila or Bembex.

All these possess stout pincers, capable of gripping, grinding and

tearing. Then what is the purpose of the Leucopsis' invisible

implements? His method of consuming will tell us.



Like his prototype, the Anthrax, the Leucopsis does not eat the

Chalicodoma-grub, that is to say, he does not break it up into

mouthfuls; he drains it without opening it and digging into its

vitals. In him again we see exemplified that marvellous art which

consists in feeding on the victim without killing it until the meal is

over, so as always to have a portion of fresh meat. With its mouth

assiduously applied to the unhappy creature's skin, the lethal grub

fills itself and waxes fat, while the fostering larva collapses and

shrivels, retaining just enough life, however, to resist

decomposition. All that remains of the decanted corpse is the skin,

which, when softened in water and blown out, swells into a balloon

without the least escape of gas, thus proving the continuity of the

integument. All the same, the apparently unpunctured bladder has lost

its contents. It is a repetition of what the Anthrax has shown us,

with this difference, that the Leucopsis seems not so well skilled in

the delicate work of absorbing the victim. Instead of the clean white

granule which is the sole residue when the Fly has finished her joint,

the insect with the long probe has a plateful of leavings, not seldom

soiled with the brownish tinge of food that has gone bad. It would

seem that, towards the end, the act of consumption becomes more savage

and does not disdain dead meat. I also notice that the Leucopsis is

not able to get up from dinner or to sit down to it again as readily

as the Anthrax. I have sometimes to tease him with the point of a

hair-pencil in order to make him let go; and, once he has left the

joint, he hesitates a little before putting his mouth to it again. His

adhesion is not the mere result of a kiss like that of a cupping-

glass; it can only be explained by hooks that need releasing.



I now see the use of the microscopic mandibles. Those two delicate

spikes are incapable of chewing anything, but they may very well serve

to pierce the epidermis with an aperture smaller than that made by the

finest needle; and it is through this puncture that the Leucopsis

sucks the juices of his prey. They are instruments made to perforate

the bag of fat which slowly, without suffering any internal injury, is

emptied through an opening repeated here and there. The Anthrax'

cupping-glass is here replaced by piercers of exceeding sharpness and

so short that they cannot hurt anything beyond the skin. Thus do we

see in operation, with a different sort of implements, that wise

system which keeps the provisions fresh for the consumer.



It is hardly necessary to say, to those who have read the story of the

Anthrax, that this kind of feeding would be impossible with a victim

whose tissues possessed their final hardness. The Mason-bee's grub is

therefore emptied by the Leucopsis' larva while it is in a semifluid

state and deep in the torpor of the nymphosis. The last fortnight in

July and the first fortnight in August are the best times to witness

the repast, which I have seen going on for twelve and fourteen days.

Later, we find nothing in the Mason-bee's cocoon except the Leucopsis'

larva, gloriously fat, and, by its side, a sort of thin, rancid

rasher, the remains of the deceased wet-nurse. Things then remain as

they are until the hot part of the following summer or at least until

the end of June.



Then appears the nymph, which teaches us nothing striking; and at last

the perfect insect, whose hatching may be delayed until August. Its

exit from the Mason's fortress has no likeness to the strange method

employed by the Anthrax. Endowed with stout mandibles, the perfect

insect splits the ceiling of its abode by itself without much

difficulty. At the time of its deliverance, the Mason-bees, who work

in May, have long disappeared. The nests on the pebbles are all

closed, the provisioning is finished, the larvae are sleeping in their

yellow cocoons. As the old nests are utilized by the Mason so long as

they are not too much dilapidated, the dome which has just been

vacated by the Leucopsis, now more than a year old, has its other

cells occupied by the Bee's children. There is here, without seeking

farther, a fat living for the Leucopsis' offspring which she well

knows how to turn to profit. It depends but on herself to make the

house in which she was born into the residence of her family. Besides,

if she has a fancy for distant exploration, clay domes abound in the

harmas. The inoculation of the eggs through the walls will begin

shortly. Before witnessing this curious performance, let us examine

the needle that is to effect it.



The insect's abdomen is hollowed, at the top, into a furrow that runs

up to the base of the thorax; the end, which is broader and rounded,

has a narrow slit, which seems to divide this region into two. The

whole thing suggests a pulley with a fine groove. When at rest, the

inoculating-needle or ovipositor remains packed in the slit and the

furrow. The delicate instrument thus almost completely encircles the

abdomen. Underneath, on the median line, we see a long, dark-brown

scale, pointed, keel-shaped, fixed by its base to the first abdominal

segment, with its sides prolonged into membranous wings which are

fastened tightly to the insect's flanks. Its function is to protect

the underlying region, a soft-walled region in which the probe has its

source. It is a cuirass, a lid which protects the delicate motor-

machinery during periods of inactivity but swings from back to front

and lifts when the implement has to be unsheathed and used.



We will now remove this lid with the scissors, so as to have the whole

apparatus before our eyes, and then raise the ovipositor with the

point of a needle. The part that runs along the back comes loose

without the slightest difficulty, but the part embedded in the groove

at the end of the abdomen offers a resistance that warns us of a

complication which we did not notice at first. The tool, in fact,

consists of three pieces, a central piece, or inoculating-filament,

and two side-pieces, which together constitute a scabbard. The two

latter are more substantial, are hollowed out like the sides of a

groove and, when uniting, form a complete groove in which the filament

is sheathed. This bivalvular scabbard adheres loosely to the dorsal

part; but, farther on, at the tip of the abdomen and under the belly,

it can no longer be detached, as its valves are welded to the

abdominal wall. Here, therefore, we find, between the two joined

protecting parts, a simple trench in which the filament lies covered

up. As for this filament, it is easily extracted from its sheath and

released down to its base, under the shield formed by the scale.



Seen under the magnifying-glass, it is a round, stiff, horny thread,

midway in thickness between a human hair and a horse-hair. Its tip is

a little rough, pointed and bevelled to some length down. The

microscope becomes necessary if we would see its real structure, which

is much less simple than it at first appears. We perceive that the

bevelled end-part consists of a series of truncated cones, fitting one

into the other, with their wide base slightly projecting. This

arrangement produces a sort of file, a sort of rasp with very much

blunted teeth. When pressed on the slide, the thread divides into four

pieces of unequal length. The two longer end in the toothed bevel.

They come together in a very narrow groove, which receives the two

other, rather shorter pieces. These both end in a point, which,

however, is not toothed and does not project as far as the final rasp.

They also unite to form a groove, which fits into the groove of the

other two, the whole constituting a complete channel or duct.

Moreover, the two shorter pieces, considered together, can move,

lengthwise, in the groove that receives them; they can also move one

over the other, always lengthwise, so much so that, on the slide of

the microscope, their terminal points are seldom situated on the same

level.



If with our scissors we cut a piece of the inoculating-thread from the

living insect and examine the section under the magnifying-glass, we

shall see the inner groove lengthen out and project beyond the outer

groove and then go in again in turn, while from the wound there oozes

a tiny albimunous drop, doubtless proceeding from the liquid that

gives the egg the singular appendage to which we shall come presently.

By means of these longitudinal movements of the inner trench inside

the outer trench and of the sliding, one over the other, of the two

portions of the former, the egg can be despatched to the end of the

ovipositor notwithstanding the absence of any muscular contraction,

which is impossible in a horny conduit.



We have only to press the upper surface of the abdomen to see it

disjoint itself from the first segment, as though the insect had been

cut almost in two at that point. A wide gap or hiatus appears between

the first and second rings; and, under a thin membrane, the base of

the ovipositor bulges out, bent back into a stout hook. Here the

filament passes through the insect from end to end and emerges

underneath. Its issue is therefore near the base of the abdomen,

instead of at the tip, as usual. This curious arrangement has the

effect of shortening the lever-arm of the ovipositor and bringing the

starting-point of the filament nearer to the fulcrum, namely, the legs

of the insect, and of thus assisting the difficult task of inoculation

by making the most of the effort expended.



To sum up, the ovipositor when at rest goes round the abdomen.

Starting at the base, on the lower surface, it runs round the belly

from front to back and then returns from back to front on the upper

surface, where it ends at almost the same level as its starting-point.

Its length is 14 millimetres. (.546 inch--Translator's Note.) This

fixes the limit of the depth which the probe is able to reach in the

Mason-bee's nests.



One last word on the Leucopsis' weapon. In the dying insect, beheaded,

stripped of legs and wings, with a pin stuck through its body, the

sides of the fissure containing the inoculating-thread quiver

violently, as if the belly were going to open, divide in two along the

median line and then reunite its two halves. The thread itself gives

convulsive tremblings; it comes out of its scabbard, goes back and

slips out again. It is as though the laying-implement could not

persuade itself to die before accomplishing its mission. The insect's

supreme aim is the egg; and, so long as the least spark of life

remains, it makes dying efforts to lay.



Leucopsis gigas exploits the nests of the Mason-bee of the Pebbles and

the Mason-bee of the Sheds with equal zest. To observe the insertion

of the egg at my ease and to watch the operator at work over and over

again, I gave the preference to the last-named Mason, whose nests,

removed from the neighbouring roofs by my orders, have hung for some

years in the arch of my basement. These clay hives fastened to tiles

supply me with fresh records each summer. I am much indebted to them



in the matter of the Leucopsis' life-history.



By way of comparison with what took place under my roof, I used to

observe the same scenes on the pebbles of the surrounding wastelands.

My excursions, alas, did not all reward my zeal, which zeal was not

without merit in the merciless sunshine; but still, at rare intervals,

I succeeded in seeing some Leucopsis digging her probe into the mortar

dome. Lying flat on the ground, from the beginning to the end of the

operation, which sometimes lasted for hours, I closely watched the

insect in its every movement, while my Dog, weary of being out of

doors in that scorching heat, would discreetly retire from the fray

and, with his tail between his legs and his tongue hanging out, go

home and stretch himself at full length on the cool tiles of the hall.

How wise he was to scorn this pebble-gazing! I would come in half-

roasted, as brown as a berry, to find my friend Bull wedged into a

corner, his back to the wall, sprawling on all fours, while, with

heaving sides, he panted forth the last sprays of steam from his

overheated interior. Yes, he was much better-advised to return as fast

as he could to the shade of the house. Why does man want to know

things? Why is he not indifferent to them, with the lofty philosophy

of the animals? What interest can anything have for us that does not

fill our stomachs? What is the use of learning? What is the use of

truth, when profit is all that matters? Why am I--the descendant, so

they tell me, of some tertiary Baboon--afflicted with the passion for

knowledge from which Bull, my friend and companion, is exempt?

Why...oh, where have I got to? I was going in, wasn't I, with a

splitting headache? Quick, let us get back to our subject!



It was in the first week of July that I saw the inoculation begin on

my Chalicodoma sicula nests. The parasite is at her task in the

hottest part of the day, close on three o'clock in the afternoon; and

work goes on almost to the end of the month, decreasing gradually in

activity. I count as many as twelve Leucopses at a time on the most

thickly-populated pair of tiles. The insect slowly and awkwardly

explores the nests. It feels the surface with its antennae, which are

bent at a right angle after the first joint. Then, motionless, with

lowered head, it seems to meditate and to debate within itself on the

fitness of the spot. Is it here or somewhere else that the coveted

larva lies? There is nothing outside, absolutely nothing, to tell us.

It is a stony expanse, bumpy but yet very uniform in appearance, for

the cells have disappeared under a layer of plaster, a work of public

interest to which the whole swarm devotes its last days. If I myself,

with my long experience, had to decide upon the suitable point, even

if I were at liberty to make use of a lens for examining the mortar

grain by grain and to auscultate the surface in order to gather

information from the sound emitted, I should decline the job,

persuaded in advance that I should fail nine times out of ten and only

succeed by chance.



Where my discernment, aided by reason and my optical contrivances,

fails, the insect, guided by the wands of its antennae, never

blunders. Its choice is made. See it unsheathing its long instrument.

The probe points normally towards the surface and occupies nearly the

central spot between the two middle-legs. A wide dislocation appears

on the back, between the first and second segments of the abdomen; and

the base of the instrument swells like a bladder through this opening;

while the point strives to penetrate the hard clay. The amount of

energy expended is shown by the way in which the bladder quivers. At



every moment we expect to see the frail membrane burst with the

violence of the effort. But it does not give way; and the wire goes

deeper and deeper.



Raising itself high on its legs, to give free play to its apparatus,

the insect remains motionless, the only sign of its arduous labours

being a slight vibration. I see some perforators who have finished

operating in a quarter of an hour. These are the quickest at the

business. They have been lucky enough to come across a wall which is

less thick and less hard than usual. I see others who spend as many as

three hours on a single operation, three long hours of patient

watching for me, in my anxiety to follow the whole performance to the

end, three long hours of immobility for the insect, which is even more

anxious to make sure of board and lodging for its egg. But then is it

not a task of the utmost difficulty to introduce a hair into the

thickness of a stone? To us, with all the dexterity of our fingers, it

would be impossible; to the insect, which simply pushes with its

belly, it is just hard work.



Notwithstanding the resistance of the substance traversed, the

Leucopsis perseveres, certain of succeeding; and she does succeed,

although I am still unable to understand her success. The material

through which the probe has to penetrate is not a porous substance; it

is homogeneous and compact, like our hardened cement. In vain do I

direct my attention to the exact point where the instrument is at

work; I see no fissure, no opening that can facilitate access. A

miner's drill penetrates the rock only by pulverizing it. This method

is not admissible here; the extreme delicacy of the implement is

opposed to it. The frail stem requires, so it seems to me, a ready-

made way, a crevice through which it can slip; but this crevice I have

never been able to discover. What about a dissolving fluid which would

soften the mortar under the point of the ovipositor? No, for I see not

a trace of humidity around the point where the thread is at work. I

fall back upon a fissure, a lack of continuity somewhere, although my

examination fails to discover any on the Mason-bee's nest. I was

better served in another case. Leucopsis dorsigera, FAB., settles her

eggs on the larva of the Diadem Anthidium, who sometimes makes her

nest in reed-stumps. I have repeatedly seen her insert her auger

through a slight rupture in the side of the reed. As the wall was

different, wood in the latter case and mortar in the former, perhaps

it will be best to look upon the matter as a mystery.



My sedulous attendance, during the best part of July, in front of the

tiles hanging from the walls of the arch, allowed me to reckon the

inoculations. Each time that the insect, on finishing the operation,

removed its probe, I marked in pencil the exact point at which the

instrument was withdrawn; and I wrote down the date beside it. This

information was to be utilized when the Leucopsis finished her

labours.



When the perforators are gone, I proceed with my examination of the

nests, covered with my hieroglyphics, the pencilled notes. One result,

one which I fully expected, compensates me straightway for all my

weary waitings. Under each spot marked in black, under each spot

whence I saw the ovipositor withdrawn, I always find a cell, with not

a single exception. And yet there are intervals of solid stone between

the cells: the partition-walls alone would account for some. Moreover,

the compartments, which are very irregularly disposed by a swarm of

toilers who all work in their own sweet way, have great irregular

cavities between them, which end by being filled up with the general

plastering of the nest. The result of this arrangement is that the

massive portions cover almost the same space as the hollow portions.

There is nothing outside to show whether the underlying regions are

full or empty. It is quite impossible for me to decide if, by digging

straight down, I shall come to a hollow cell or to a solid wall.



But the insect makes no mistake: the excavations under my pencil-marks

bear witness to that; it always directs its apparatus towards the

hollow of a cell. How is it apprised whether the part below is empty

or full? Its organs of information are undoubtedly the antennae, which

feel the ground. They are two fingers of unparalleled delicacy, which

pry into the basement by tapping on the part above it. Then what do

those puzzling organs perceive? A smell? Not at all; I always had my

doubts of that and now I am certain of the contrary, after what I

shall describe in a moment. Do they perceive a sound? Are we to treat

them as a superior kind of microphone, capable of collecting the

infinitesimal echoes of what is full and the reverberations of what is

empty? It is an attractive idea, but unfortunately the antennae play

their part equally well on a host of occasions when there are no

vaults to reverberate. We know nothing and are perhaps destined never

to know anything of the real value of the antennal sense, to which we

have nothing analogous; but, though it is impossible for us to say

what it does perceive, we are at least able to recognize to some

extent what it does not perceive and, in particular, to deny it the

faculty of smell.



As a matter of fact, I notice, with extreme surprise, that the great

majority of the cells visited by the Leucopsis' probe do not contain

the one thing which the insect is seeking, namely, the young larva of

the Mason-bee enclosed in its cocoon. Their contents consist of the

refuse so often met with in old Chalicodoma-nests: liquid honey left

unemployed, because the egg has perished; spoilt provisions, sometimes

mildewed, or sometimes a tarry mass; a dead larva, stiffened into a

brown cylinder; the shrivelled corpse of a perfect insect, which

lacked the strength to effect its deliverance; dust and rubbish which

has come from the exit-window afterwards closed up by the outer

coating of plaster. The odoriferous effluvia that can emanate from

these relics certainly possess very diverse characters. A sense of

smell with any subtlety at all would not be deceived by this stuff,

sour, 'high,' musty or tarry as the case may be; each compartment,

according to its contents, has a special aroma, which we might or

might not be able to perceive; and this aroma most certainly bears no

resemblance to that which we may assume the much-desired fresh larva

to possess. If nevertheless the Leucopsis does not distinguish between

these various cells and drives the probe into all of them

indifferently, is this not an evident proof that smell is no guide

whatever to her in her search? Other considerations, when I was

treating of the Hairy Ammophila, enabled me to assert that the

antennae have no olfactory powers. To-day, the frequent mistakes of

the Leucopsis, whose antennae are nevertheless constantly exploring

the surface, make this conclusion absolutely certain.



The perforator of clay nests has, so it seems to me, delivered us from

an old physiological fallacy. She would deserve studying, if for no

other result than this; but her interest is far from being exhausted.

Let us look at her from another point of view, whose full importance

will not be apparent until the end; let us speak of something which I

was very far from suspecting when I was so assiduously watching the

nests of my Mason-bees.



The same cell can receive the Leucopsis' probe a number of times, at

intervals of several days. I have said how I used to mark in black the

exact place at which the laying-implement had entered and how I wrote

the date of the operation beside it. Well, at many of these already

visited spots, concerning which I possessed the most authentic

documents, I saw the insect return a second, a third and even a fourth

time, either on the same day or some while after, and drive its

inoculating-thread in again, at precisely the same place, as though

nothing had happened. Was it the same individual repeating her

operation in a cell which she had visited before but forgotten, or

different individuals coming one after the other to lay an egg in a

compartment thought to be unoccupied? I cannot say, having neglected

to mark the operators, for fear of disturbing them.



As there is nothing, except the mark of my pencil, a mark devoid of

meaning to the insect, to indicate that the auger has already been at

work there, it may easily happen that the same operator, finding under

her feet a spot already exploited by herself but effaced from her

memory, repeats the thrust of her tool in a compartment which she

believes herself to be discovering for the first time. However

retentive its memory for places may be, we cannot admit that the

insect remembers for weeks on end, as well as point by point, the

topography of a nest covering a surface of some square yards. Its

recollections, if it have any, serve it badly; the outward appearance

gives it no information; and its drill enters wherever it may happen

to discover a cell, at points that have already perhaps been pierced

several times over.



It may also happen--and this appears to me the most frequent case--

that one exploiter of a cell is succeeded by a second, a third, a

fourth and others still, all fired with the newcomer's zeal because

their predecessors have left no trace of their passage. In one way or

another, the same cell is exposed to manifold layings, though its

contents, the Chalicodoma-grub, be only the bare ration of a single

Leucopsis-grub.



These reiterated borings are not at all rare: I noted a score of them

on my tiles; and, in the case of some cells, the operation was

repeated before my eyes as often as four times. Nothing tells us that

this number was not exceeded in my absence. The little that I observed

prevents me from fixing any limit. And now a momentous question

arises: is the egg really laid each time that the probe enters a cell?

I can see not the slightest excuse for supposing the contrary. The

ovipositor, because of its horny nature, can have but a very dull

sense of touch. The insect is apprised of the contents of the cell

only by the end of that long horse-hair, a not very trustworthy

witness, I should imagine. The absence of resistance tells it that it

has reached an empty space; and this is probably the only information

that the insensible implement can supply. The drill boring through the

rock cannot tell the miner anything about the contents of the cavern

which it has entered; and the case must be the same with the rigid

filament of the Leucopses.



Now that the thread has reached its goal, what does the cell contain?

Mildewed honey, dust and rubbish, a shrivelled larva, or a larva in

good condition? Above all, does it already contain an egg? This last

question calls for a definite answer, but as a matter of fact it is

impossible for the insect to learn anything from a horse-hair on that

most delicate matter, the presence or absence of an egg, a mere atom

of a thing, in that vast apartment. Even admitting some sense of touch

at the end of the drill, one insuperable difficulty would always

remain: that of finding the exact spot where the tiny speck lies in

those spacious and mysterious regions. I go so far as to believe that

the ovipositor tells the insect nothing, or at any rate very little,

of the inside of the cell, whether propitious or not to the

development of the germ. Perhaps each thrust of the instrument,

provided that it meets with no resistance from solid matter, lays the

egg, to whose lot there falls at one time good, wholesome food, at

another mere refuse.



These anomalies call for more conclusive proofs than the rough

deductions drawn from the nature of the horny ovipositor. We must

ascertain in a direct fashion whether the cell into which the auger

has been driven several times over actually contains several occupants

in addition to the larva of the Mason-bee. When the Leucopses had

finished their borings, I waited a few days longer so as to give the

young grubs time to develop a little, which would make my examination

easier. I then moved the tiles to the table in my study, in order to



investigate their secrets with the most scrupulous care. And here such

a disappointment as I have rarely known awaited me. The cells which I

had seen, actually seen, with my own eyes, pierced by the probe two or

three or even four times, contained but one Leucopsis-grub, one alone,

eating away at its Chalicodoma. Others, which had also been repeatedly

probed, contained spoilt remnants, but never a Leucopsis. O holy

patience, give me the courage to begin again! Dispel the darkness and

deliver me from doubt!



I begin again. The Leucopsis-grub is familiar to me; I can recognize

it, without the possibility of a mistake, in the nests of both the

Chalicodoma of the Pebbles and the Chalicodoma of the Sheds. All

through the winter, I rush about, getting my nests from the roofs of

old sheds and the pebbles of the waste-lands; I stuff my pockets with

them, fill my box, load Favier's knapsack; I collect enough to litter

all the tables in my study; and, when it is too cold out of doors,

when the biting mistral blows, I tear open the fine silk of the

cocoons to discover the inhabitant. Most of them contain the Mason in

the perfect state; others give me the larva of the Anthrax; others--

very numerous, these--give me the larva of the Leucopsis. And this

last is alone, always alone, invariably alone. The whole thing is

utterly incomprehensible when one knows, as I know, how many times the

probe entered those cells.



My perplexity only increases when, on the return of summer, I witness

for the second time the Leucopsis' repeated operations on the same

cells and for the second time find a single larva in the compartments

which have been bored several times over. Shall I then be forced to

accept that the auger is able to recognize the cells already

containing an egg and that it thenceforth refrains from laying there?

Must I admit an extraordinary sense of touch in that bit of horse-

hair, or even better, a sort of divination which declares where the

egg lies without having to touch it? But I am raving! There is

certainly something that escapes me; and the obscurity of the problem

is simply due to my incomplete information. O patience, supreme virtue

of the observer, come to my aid once more! I must begin all over again

for the third time.



Until now, my investigations have been made some time after the

laying, at a period when the larva is at least fairly developed. Who

knows? Something perhaps happens, at the very commencement of infancy,

that may mislead me afterwards. I must apply to the egg itself if I

would learn the secret which the grub will not reveal. I therefore

resume my observations in the first fortnight of July, when the

Leucopses are beginning to visit busily both Mason-bee's nests. The

pebbles in the waste-lands supply me with plenty of buildings of the

Chalicodoma of the Walls; the byres scattered here and there in the

fields give me, under their dilapidated roofs, in fragments broken off

with the chisel, the edifices of the Chalicodoma of the Sheds. I am

anxious not to complete the destruction of my home hives, already so

sorely tried by my experiments; they have taught me much and can teach

me more. Alien colonies, picked up more or less everywhere, provide me

with my booty. With my lens in one hand and my forceps in the other, I

go through my collection on the same day, with the prudence and care

which only the laboratory-table permits. The results at first fall far

short of my expectations. I see nothing that I have not seen before. I

make fresh expeditions, after a few days' interval; I bring back fresh

loads of lumps of mortar, until at last fortune smiles upon me.



Reason was not at fault. Each thrust means the laying of an egg when

the probe reaches the cell. Here is a cocoon of the Mason-bee of the

Pebbles with an egg side by side with the Chalicodoma-grub. But what a

curious egg! Never have my eyes beheld the like; and then is it really

the egg of the Leucopsis? Great was my apprehension. But I breathed

again when I found, a couple of weeks later, that the egg had become

the larva with which I was familiar. Those cocoons with a single egg

are as numerous as I can wish; they exceed my wishes: my little glass

receptacles are too few to hold them.



And here are others, more precious ones still, with manifold layings.

I find plenty with two eggs; I find some with three or four; the best-

colonised offer me as many as five. And, to crown my delight, the joy

of the seeker to whom success comes at the last moment, when he is on

the verge of despair, here again, duly furnished with an egg, is a

sterile cocoon, that is to say, one containing only a shrivelled and

decaying larva. All my suspicions are confirmed, down to the most

inconsequent: the egg housed with a mass of putrefaction.



The nests of the Mason-bee of the Walls are the more regular in

structure and are easier to examine, because their base is wide open

once it is separated from the supporting pebble; and it was these

which supplied me with by far the greater part of my information.

Those of the Mason-bee of the Sheds have to be chipped away with a

hammer before one can inspect their cells, which are heaped up anyhow;

and they do not lend themselves anything like so well to delicate

investigations, as they suffer both from the shock and the ill-

treatment.



And now the thing is done: it remains certain that the Leucopsis'

laying is exposed to very exceptional dangers. She can entrust the egg

to sterile cells, without provisions fit to use; she can establish

several in the same cell, though this cell contains nourishment for

one only. Whether they proceed from a single individual returning

several times, by inadvertence, to the same place, or are the work of

different individuals unaware of the previous borings, those multiple

layings are very frequent, almost as much so as the normal layings.

The largest which I have noticed consisted of five eggs, but we have

no authority for looking upon this number as an outside limit. Who

could say, when the perforators are numerous, to what lengths this

accumulation can go? I will set forth on some future occasion how the

ration of one egg remains in reality the ration of one egg, despite

the multiplicity of banqueters.



I will end by describing the egg, which is a white, opaque object,

shaped like a much-elongated oval. One of the ends is lengthened out

into a neck or pedicle, which is as long as the egg proper. This neck

is somewhat wrinkled, sinuous and as a rule considerably curved. The

whole thing is not at all unlike certain gourds with an elongated

paunch and a snake-like neck. The total length, pedicle and all, is

about 3 millimetres. (About one-eighth of an inch.--Translator's

Note.) It is needless to say, after recognizing the grub's manner of

feeding, that this egg is not laid inside the fostering larva. Yet,

before I knew the habits of the Leucopsis, I would readily have

believed that every Hymenopteron armed with a long probe inserts her

eggs into the victim's sides, as the Ichneumon-flies do to the

Caterpillars. I mention this for the benefit of any who may be under

the same erroneous impression.



The Leucopsis' egg is not even laid upon the Mason-bee's larva; it is

hung by its bent pedicle to the fibrous wall of the cocoon. When I go

to work very delicately, so as not to disturb the arrangement in

knocking the nest off its support, and then extract and open the

cocoon, I see the egg swinging from the silken vault. But it takes

very little to make it fall. And so, most often, even though it be

merely the effect of the shock sustained when the nest is removed from

its pebble, I find the egg detached from its suspension-point and

lying beside the larva, to which it never adheres in any

circumstances. The Leucopsis' probe does not penetrate beyond the

cocoon traversed; and the egg remains fastened to the ceiling, in the

crook of some silky thread, by means of its hooked pedicle.





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