Réaumur has dedicated one of his studies to the Chalicodoma of walls,
which he calls the Mason Bee. I propose to resume this study, to
complete it, and especially to consider it from a point of view
entirely neglected by that illustrious observer. And first of all I am
tempted to state how I made acquaintance with this Hymenopteron. It was
when I first began to teach—towards A.D. 1843. On leaving the Normal
School of Vaucluse a few months previously, with my certificate, and
the naïve enthusiasm of eighteen, I was sent to Carpentras to manage
the primary school belonging to the college. A singular school it was,
upon my word, notwithstanding its fine title of “Upper”!—a kind of vast
cellar breathing out the damp engendered by a fountain backing on it in
the street. Light came in through a door opening outward when the
weather allowed of it, and a narrow prison-window, with iron-bars, and
little diamond panes set in lead. For seats there was a plank fastened
to the walls all round the room; in the middle was a chair guiltless of
straw, a blackboard, and a bit of chalk.
Morning and evening, at the sound of a bell, there tumbled in some
fifty young rascals, who, having failed to master De viris and the
Epitome, were devoting themselves, as one said then, to “some good
years of French.” The failures at “Rosa, a Rose,” came to me to learn a
little spelling. Children were mingled with tall lads at various stages
of education, and all distressingly agreed in playing tricks on the
master—no older, even younger, than some of themselves.
I taught the little ones to read syllables, the middle ones to hold a
pen in the right way while writing a few words of dictation on their
knees; for the eldest I unveiled the secrets of fractions, and even the
mysteries of the hypotenuse. And the only means I had to keep this
restless crowd in order, give each mind appropriate food, arouse
attention, expel dulness from the gloomy room whose very walls dripped
melancholy, were my tongue and a bit of chalk.
For that matter there was equal disdain in the other classes for all
which was not Latin or Greek. One instance will suffice to show the
style in which physical science was treated, now so large a part of
education. The principal of this college was an excellent man—the
worthy Abbé X, who, not anxious himself to grow green peas and bacon,
turned over such matters to some relation of his, and undertook to
teach physical science.
Let us attend one of his lessons, which happens to be on the barometer.
By good luck the college owned one. It was an old article, very dusty,
hung high out of reach of profane hands, and bearing on its face in
large letters the words, Storm, Rain, Fine. “The barometer,” began the
good abbé, addressing himself to his disciples—he used a fatherly
second person singular to each,—“the barometer gives notice of good or
bad weather. Thou seest the words written here—Storm, Rain—thou seest,
Bastien?” “I see,” replies Bastien, the most mischievous of the troop.
He has run through his book, and knows more about the barometer than
does his professor. “It is composed,” the abbé goes on, “of a curved
glass tube full of mercury which rises and falls according to the
weather. The small branch of this tube is open; the other—the other—we
shall see as to the other. Bastien—Get on this chair, and just feel
with the tip of thy finger if the long branch is open or closed. I do
not quite remember.” Bastien goes to the chair, stands as high as he
can on tip-toe, and feels the top of the long column with a finger tip.
Then, with a slight smile under the down of his dawning moustache, he
replies, “Yes, exactly; yes, the long branch is open at the top. I can
feel the hollow.” And to corroborate his mendacious statement he went
on moving his forefinger on the top of the tube, while his
co-disciples, accomplices in mischief, stifled their laughter as best
they could. The abbé said calmly, “That will do. Come down, Bastien.
Gentlemen, write in your notes that the long branch of the barometer is
open. You might forget it. I had forgotten it myself.”
Thus were physics taught. Things mended, however; a master came, and
came to stay,—one who knew that the long branch of a barometer is
closed. I obtained tables on which my pupils could write instead of
scrawling on their knees, and as my class grew daily larger, it ended
by being divided. As soon as I had an assistant to look after the
younger ones, things changed for the better.
Among the subjects taught, one pleased master and pupils equally. This
was out-of-door geometry, practical surveying. The college had none of
the necessary outfit, but with my large emoluments—700 francs, if you
please!—I could not hesitate as to making the outlay. A measuring chain
and stakes, a level, square, and compass were bought at my expense. A
tiny graphometer, hardly bigger than one’s palm, and worth about 4s.
2d., was furnished by the college. We had no tripod, and I had one
made. In short, my outfit was complete. When May came, once a week the
gloomy class-room was exchanged for the fields, and we all felt it as a
holiday. There were disputes as to the honour of carrying the stakes,
divided into packets of three, and more than one shoulder as we went
through the town felt glorified in the sight of all by the learned
burden. I myself—why conceal it?—was not without a certain satisfaction
at carrying tenderly the most precious part of the apparatus, the
famous four-and-twopenny graphometer. The scene of operations was an
uncultivated pebbly plain—a harmas, as we call it in these parts. No
curtain of live hedge, no bushes, hindered me from keeping an eye upon
my followers; here—an all important condition—I need not fear
temptation from green apricots for my scholars. There was free scope
for all imaginable polygons; trapezes and triangles might be joined at
will. Wide distances suggested plenty of elbow room, and there was even
an ancient building, once a dovecote, which lent its vertical lines to
the service of the graphometer.
Now from the very first a suspicious something caught my attention. If
a scholar were sent to plant a distant stake I saw him frequently
pause, stoop, rise, seek about, and stoop again, forgetful of straight
line and of signals. Another, whose work it was to pick up pegs, forgot
the iron spike and took a pebble instead; and a third, deaf to the
measurements of the angle, crumbled up a clod. The greater number were
caught licking a bit of straw, and polygons stood still, and diagonals
came to grief. What could be the mystery? I inquired, and all was
explained. Searcher and observer born, the scholar was well aware of
what the master was ignorant of—namely, that a great black bee makes
earthen nests on the pebbles of the harmas, and that in these nests
there is honey. My surveyors were opening and emptying the cells with a
straw. I was instructed in the proper method. The honey, though
somewhat strong-flavoured, is very acceptable; I in turn acquired a
taste for it, and joined the nest-hunters. Later, the polygon was
resumed. Thus it was that for the first time I saw Réaumur’s Mason Bee,
knowing neither its history nor its historian.
This splendid Hymenopteron, with its dark violet wings and costume of
black velvet, its rustic constructions on the sun-warmed pebbles among
the thyme, its honey, which brought diversion from the severities of
compass and square, made a strong impression on my mind, and I wished
to know more about it than my pupils had taught me—namely, how to rob
the cells of their honey with a straw. Just then my bookseller had for
sale a magnificent work on insects, The Natural History of Articulated
Animals, by de Castelnau, E. Blanchard, and Lucas. It was enriched with
many engravings which caught the eye. But alas, it had a price—such a
price! What did that matter? My 700 francs ought surely to suffice for
everything—food for the mind as well as for the body. That which I
bestowed on the one I retrenched from the other—a balance of accounts
to which whoever takes science for a livelihood must needs resign
himself. The purchase was made. That day I bled my university stipend
abundantly; I paid away a whole month of it. It took a miracle of
parsimony to fill up the enormous deficit.
The book was devoured—I can use no other word. There I learned the name
of my black bee, and there I read for the first time details of the
habits of insects, and found, with what seemed to my eyes an aureole
round them, the venerated names of Réaumur, Huber, Léon Dufour; and
while I turned the pages for the hundredth time, a voice whispered
vaguely, “Thou too shalt be a historian of animals!” Naïve illusions!
where are you? But let us banish these recollections, both sweet and
sad, and come to the doings of our black bee.
Chalicodoma, house of pebbles, rough-cast mortar, a name which would be
perfect did it not look odd to any one not well up in Greek. It is a
name applied to those Hymenoptera that build cells with materials such
as we use for our dwellings. It is masonry, but made by a rustic
workman, better used to dried clay than to hewn stone. A stranger to
scientific classification (and this causes great obscurity in some of
his memoirs), Réaumur called the worker after the work, and named our
builders in dried clay Mason Bees, which paints them exactly. We have
two kinds, C. muraria, whose history is admirably given by Réaumur, and
C. sicula, which is not special to the land of Etna, as the name
suggests, but is found in Greece, Algeria, and the Mediterranean region
of France, especially in the department of Vaucluse, where in May it is
one of the most common Hymenoptera. The two sexes of C. muraria are so
unlike in colouring that a novice observing both coming out of the same
nest would take them for strangers to one another. The female is of a
splendid velvet black, with dark violet wings; in the male the black
velvet is replaced by a bright iron-red fleece. The second species—a
much smaller one—has not this difference of colour, both sexes wearing
the same costume—a general mixture of brown, red, and ashy tints. Both
begin to build in the beginning of May. The wing-tips, washed with
violet on a bronze ground, faintly recall the rich purple of the first
species.
As Réaumur tells us, C. muraria in the northern provinces chooses as
the place to fix her nest a wall well exposed to the sun and not
plastered, as the plaster might come off and endanger her cells. She
only entrusts her constructions to a solid foundation, such as a bare
stone. I see that she is equally prudent in the south, but, for some
reason unknown to me, she generally chooses some other base than the
stone of a wall. A rolled pebble, often hardly larger than one’s
fist,—one of those with which the waters of the glacial period covered
the terraces of the Rhône valley,—is her favourite support. The great
ease with which such a one is found may influence her; all our slightly
raised plateaux, all our arid thyme-clad ground, are but heaped pebbles
cemented with red earth. In the valleys the bee can also use the stones
gathered in torrent beds; near Orange, for instance, her favourite
spots are the alluviums of the Aygues, with their stretches of rolled
boulders no longer visited by water. Or if a pebble be wanting, she
will establish her nest on a boundary stone or an enclosing wall.
Chalicodoma sicula has a yet greater variety of choice. Her favourite
position is under a tile projecting from the edge of a roof. There is
scarcely a little dwelling in the fields that does not thus shelter her
nests. There, every spring, she establishes populous colonies, whose
masonry, transmitted from one generation to another, and yearly
enlarged, finally covers a very considerable surface. I have seen such
a one under the tiles of a shed, which spread over five or six square
yards. When the colony were hard at work, their number and humming
fairly made one dizzy. The underpart of a balcony pleases them equally,
or the frame of an unused window,—above all, if closed by a
sun-shutter, which offers a free passage. But these are great
meeting-places, where labour, each for herself, hundreds and thousands
of workers. If alone, which not seldom occurs, Chalicodoma sicula
establishes herself in the first little spot she can find, so long as
it has a solid basis and heat. As for the nature of this basis it
matters little. I have seen nests built on bare stones and brick, on a
shutter, and even on the glass panes in a shed. One thing only does not
suit the bee—namely, the stucco of our houses. Prudent, like her
retainer C. muraria, she would fear ruin to her cells did she entrust
them to a support which might fall.
Finally, for reasons which I cannot yet satisfactorily explain, C.
sicula often entirely changes her manner of building, turning her heavy
mortar dwelling, which seems to require a rock to support it, into an
aerial one, hung to a bough. A bush in a hedge,—no matter
what—hawthorn, pomegranate, or Paliurus,—offers a support, usually
about the height of a man, Ilex and elm give a greater height. The bee
chooses in some thicket a bough about as thick as a straw, and
constructs her edifice on this narrow base with the same mortar which
would be used under a balcony or the projecting edge of a roof. When
finished, the nest is a ball of earth, traversed literally by the
bough. If made by a single insect it is the size of an apricot, and of
a fist if several have worked at it; but this seldom occurs.
Both species use the same materials, a calcareous clay, mixed with a
little sand and kneaded with the mason’s own saliva. Damp spots which
would facilitate labour and spare saliva to mix mortar are disdained by
the Chalicodoma, which refuses fresh earth for building, just as our
builders refuse old plaster and lime. Such materials when soaked with
humidity would not hold properly. What is needed is a dry powder, which
readily absorbs the disgorged saliva, and forms with the albuminous
principles of this liquid a kind of Roman cement, hardening
quickly,—something like what we obtain with quicklime and white of egg.
A beaten road, formed of calcareous boulders crushed by passing wheels
into a smooth surface like paving stones, is the quarry whence
Chalicodoma sicula prefers to get mortar; whether she builds on a
branch, in a hedge, or under the jutting roof of some rural habitation,
it is always from a neighbouring path, or a road, or the highway, that
she seeks materials—indifferent to the constant passing of beasts and
travellers. You should see the active bee at work when the road is
dazzling white in the hot sunshine. Between the neighbouring farm where
she is building and the road where the mortar is prepared, there is the
deep hum of the bees perpetually crossing each other as they come and
go. The air seems traversed by constant trails of smoke, so rapid and
direct is their flight. Those who go carry away a pellet of mortar as
big as small shot; those who come settle on the hardest and driest
spots. Their whole body vibrates as they scratch with the tips of their
mandibles, and rake with their forefeet to extract atoms of earth and
grains of sand, which, being rolled between their teeth, become moist
with saliva and unite. They work with such ardour that they will let
themselves be crushed under the foot of a passer-by rather than move.
Chalicodoma muraria, however, which seeks solitude, far from human
habitation, is rarely seen on beaten paths; perhaps they are too
distant from the places where she builds. If she can find dry earth,
rich in small gravel, near the boulder chosen as the basis of her nest,
she is contented. She may either make quite a new nest in a spot
hitherto unoccupied, or over the cells of an old one, after repairing
them. Let us consider the first case.
After choosing a boulder, she comes with a pellet of mortar in her
mandibles, and arranges it in a ring on the surface of the pebble. The
forefeet, and above all the mandibles, which are her most important
tools, work the material, which is kept plastic by the gradually
disgorged saliva. To consolidate the unbaked clay, angular pieces of
gravel, as large as a small bean, are worked in singly on the outside
of the still soft mass. This is the foundation of the edifice. Other
layers are added until the cell has the required height of three or
four centimetres. The masonry is formed by stones laid on one another
and cemented with lime, and can stand comparison with our own. True, to
economise labour and mortar, the bee uses coarse materials,—large bits
of gravel, which in her case answer to hewn blocks. They are chosen
singly—very hard ones, almost always with angles which, fitted
together, give mutual support, and add solidity to the whole. Layers of
mortar, sparingly used, hold them together. The outside of the cell
thus assumes the look of a piece of rustic architecture, in which
stones project with their natural inequalities; but over the inside,
which requires a smoother surface in order not to wound the tender skin
of the larva, is spread a wash of pure mortar—artlessly, however, as if
by broad sweeps of a trowel; and when it has eaten up its honey paste,
the grub takes care to make a cocoon and hang the rude wall of its
abode with silk. The Anthophora and Halictus, whose larvæ spin no
cocoon, varnish the inside of their earthen cells delicately, giving
them the polish of worked ivory.
The construction, the axis of which is always nearly vertical, with an
orifice opening upward, so that the fluid honey may not run out,
differs a little in form, according to its basis. On a horizontal
surface it rises like a little oval tower; on a vertical or slanting
one it resembles half a thimble cut down its length. In this case the
support—the pebble itself—completes the surrounding wall. The cell
completed, the bee sets to work at once to store it. The neighbouring
flowers, especially those of Genista scorpius, which in May turn the
alluviums of the torrents golden, furnish sugared liquid and pollen.
She comes with her crop swelled with honey, and all yellow underneath
with pollen dust, and plunges head first into the cell, where for some
moments one may see her work her body in a way which tells that she is
disgorging honey. Her crop emptied, she comes out, but only to go in
again at once—this time backwards. With her two hind feet she now frees
herself from her load, of pollen by brushing herself underneath. Again
she goes out, and returns head first. She must stir the materials with
her mandibles for a spoon, and mix all thoroughly together. This labour
of mixing is not repeated after every journey, but only from time to
time, when a considerable quantity has been collected. When the cell is
half full, it is stored; an egg must be laid on the honey paste, and
the door has to be closed. This is all done without delay. The orifice
is closed by a cover of undiluted mortar, worked from the circumference
to the centre. Two days at most seem required for the whole work,
unless bad weather or a cloudy day should interrupt it. Then, backing
on the first cell, a second is built and stored in the same way, and a
third and fourth, etc., follow, each one with honey and an egg, and
closed before another is begun. Work once begun is continued until it
is completed, the bee never building a new cell until the four acts
required to perfect the preceding one are performed—namely,
construction, provisioning, an egg, and sealing the cell.
As Chalicodoma muraria always works alone on her chosen boulder, and
shows great jealousy if her neighbours alight there, the number of
cells clustered on one pebble is not great—usually six to ten. Are some
eight larvæ her whole progeny, or will she establish a more numerous
family on other boulders? The surface of the stone would allow of more
cells if she had eggs for them, and the bee might build there very
comfortably without hunting for another, or leaving the one to which
she is attached by habit and long acquaintance. I think, therefore,
that most probably all her scanty family are settled on the same
stone—at all events when she builds a new abode.
The six or ten cells composing the group are certainly a solid
dwelling, with their rustic covering of gravel, but the thickness of
their walls and lids—two millimetres at most—hardly seems sufficient
against rough weather. Set on its stone in the open air, quite
unsheltered, the nest will undergo the heat of summer suns which will
turn every cell into an oven; then will come the autumn rains which
will slowly eat away the masonry, and then winter frosts which will
crumble what the rain may have respected. However hard the cement may
be, can it resist all these attacks, and if it can, will not the larvæ,
sheltered by so thin a wall, suffer from over-heat in summer and too
keen cold in winter?
Without having gone through all these arguments, the bee acts wisely.
When all the cells are completed she builds a thick cover over the
whole group, which, being of a material impermeable to water and almost
a non-conductor, is at once a defence against heat and cold and damp.
This material is the usual mortar, made of earth and saliva, only with
no small stones in it. The bee lays it on,—one pellet after another,
one trowelful and then a second,—till there is a layer a centimetre
thick over all the cells, which disappear entirely under it. The nest
is now a rude dome, about as big as half an orange; one would take it
for a clod of mud, half crushed by being flung against a stone where it
had dried. Nothing outside betrays its contents—no suggestion of
cells—none of labour. To the ordinary eye it is only a chance splash of
mud.
This general cover dries as rapidly as do our hydraulic cements, and
the nest is almost as hard as a stone. A knife with a strong blade is
needed to cut it. In its final shape the nest recalls in no degree the
original work; one would suppose the elegant turrets adorned with
pebble work, and the final dome, looking like a bit of mud, to be the
work of two different species. But scratch away the cover of cement and
we recognise the cells and their layers of tiny pebbles. Instead of
building on a boulder yet unoccupied, Chalicodoma muraria likes to
utilise old nests which have lasted through the year without notable
injury. The mortared dome has remained much as it was at the beginning,
so solid was the masonry; only it is pierced by a number of round holes
corresponding to the chambers inhabited by the larvæ of the past
generation. Such dwellings, only needing a little repair to put them in
good condition, economise much time and toil; so Mason Bees seek them,
and only undertake new constructions when old nests fail them.
From the same dome come forth brothers and sisters—reddish males and
black females—all descendants of the same bee. The males lead a
careless life, avoiding all labour, and only returning to their clay
dwellings for a brief courtship of their ladies; and they care nothing
for the deserted dwelling. What they want is nectar from flower-cups,
not mortar between their mandibles. But there are the young mothers,
who have sole charge of the future of the family—to which of them will
fall the inheritance of the old nest? As sisters they have an equal
right to it—so would human justice decide, now that it has made the
enormous progress of freeing itself from the old savage right of
primogeniture; but Mason Bees have not got beyond the primitive basis
of property—the right of the first comer.
So when the time to lay has come, a bee takes the first free nest which
suits her and establishes herself there, and woe to any sister or
neighbour who thenceforward disputes possession of it. A hot reception
and fierce pursuit would soon put the new-comer to flight; only one
cell is wanted at the moment out of all which gape like little wells
around the dome, but the bee calculates that by and by the rest will be
useful, and she keeps a jealous watch on them all and drives away every
visitor. I cannot remember having seen two Mason Bees working on the
same pebble.
The work is now very simple. The bee examines the inside of the old
cell to see where repairs are needed, tears down the rags of cocoon
hanging on the walls, carries out the bits of earth fallen from the
vault pierced by the inhabitant in order to get out, mortars any places
out of repair, mends the orifice a little, and that is all. Then comes
storage, laying an egg, and stopping up the cell. When these are
successively completed, the general cover, the mortar dome, is repaired
if necessary, and all is finished.
Chalicodoma sicula prefers a sociable life to a solitary one, and
hundreds—nay, several thousands—will establish themselves on the under
surface of the tiles on a hovel, or the edge of a roof. It is not a
real society with common interests, dear to all, but merely a gathering
where each works for herself and is not concerned for the rest—a throng
recalling the swarm of a hive only by their number and industry. They
use the same mortar as Chalicodoma muraria, equally resistant and
waterproof, but finer and without pebbles. First the old nests are
utilised. Every free cell is repaired, stored, and shut up. But the old
ones are far from sufficing to the population, which increases rapidly
year by year, and on the surface of the nest, where the cells are
hidden below the old general mortar covering, new ones are built as
required. They are placed more or less horizontally, one beside
another, with no kind of order. Every constructor builds as the fancy
takes her, where and as she wills; only she must not interfere with her
neighbour’s work, or rough treatment will soon call her to order. The
cells accumulate in chance fashion in this workyard, where there is no
general plan whatever. Their form is that of a thimble divided down the
axis, and their enclosure is completed either by adjacent cells, or the
surface of the old nest. Outside they are rough, and look like layers
of knotted cords corresponding to the layers of mortar. Inside the
walls are level but not smooth; a cocoon will replace the absent
polish.
As soon as a cell is built it is stored and walled up, as we have seen
with Chalicodoma muraria. This work goes on through the whole of May.
At length all the eggs are laid, and the bees, without any distinction
as to what does or does not belong to them, all set to work on a common
shelter of the colony—a thick bed of mortar, filling up spaces and
covering all the cells. In the end the nests look like a large mass of
dry mud—very irregular, arched, thickest in the middle, the primitive
kernel of the establishment, thinnest at the edges, where there are
fewest cells, and very variable in extent, according to the number of
workers, and consequently to the time when the nest was begun. Some are
not much larger than one’s hand, while others will occupy the greater
part of the edge of a roof, and be measured by square yards.
If Chalicodoma sicula works alone, as she often does, on the shutter of
an unused window or on a stone or a branch, she behaves in just the
same way. For instance, if the nest is on a bough, she begins by
solidly fixing the basis of her cell on the slender twig. Then the
building rises into a little vertical tower. This cell being stored and
ceiled, another follows, supported both by the bough and the first
cell, until six to ten cells are grouped one beside the other, and
finally a general cover of mortar encloses them all together with the
bough, which gives them a firm foundation.