CRABRO
THE highest point of the island is crowned by a great group of linden
trees; and one day their perfume, carried by the wind far over field
and wood, was calling everything that had wings to gather the richest
of all the gifts that July can offer. We, too, were drawn to the spot,
and found the great blossoming domes thrilling and vibrating with life.
For miles around, the bees, wasps, and butterflies had gathered to the
feast; and we seemed to touch the high–tide of the year in the scent of
the flowers, the humming throng of happy creatures, and the vision of
it all against the summer sky.
Below, in a great root that had pushed above ground, five little
wasps, by name sexmaculatus, of the worthy but unimaginative genus
Crabro, resisting the intoxication of the linden flowers, were sawing
and cutting in the most humdrum and practical manner. One of them,
presumably the earliest riser, was well down in the root, and came
backing up once in a while, pushing a lot of wood dust out of the
hole. This was spread out by means of legs and mandibles, and was then
blown away by the fanning wings of the little worker, who circled about
just above the ground until the last grain had disappeared. Here was
another way of protecting the home. The fresh dust might attract the
attention of some cuckoo–like insect who would lay her egg within; and
therefore it was dispersed, just as Ammophila carried out her pellet
and flung it to a distance, and Sphex spread evenly over the ground the
mass of earth that she carried from her hole.
After this series of actions had been repeated several times the wasp
flew away to hunt. We afterward found that she had finished the third
in a set of cells leading from a main gallery. On her return we delayed
her to see what she was carrying. She showed no fear, but alighted
close by, and while she was trying to transfer to the third pair of
legs the fly that she was clasping with the second pair, it escaped and
flew gayly away. Flies are plenty, however, and she soon had another
which she was permitted to store; and from that time she worked busily
until we left her at noon. It took her from two to ten minutes to
catch her fly, and at each return two or three minutes were spent in
the nest. On opening her tunnel some days later, we found within not
only flies, but long–bodied gnats, and all of them seemed to have been
brought home uninjured. When the freshest cell was opened some flew
away, others were walking about, and all were lively. The wasp egg
was laid on the under side of the neck; and although we could not be
certain of the exact time of laying we thought it hatched at the end
of thirty–six hours. From ten to sixteen flies were provided for each
larva.
[Illustration: SEXMACULATUS IN THE LINDEN ROOTS]
A month later we found Crabro lentus nesting in the ground. Her
tunnel ran down obliquely for six and one half centimeters, and had
an enlargement at the end. Two bugs and a fly were in the nest, when
we opened it before the provision was completed. To find sexmaculatus
taking both flies and gnats was surprising, so rigid are the family
traditions of the wasps; still, she might feel that so long as she drew
the line at Diptera she was all right. But to believe that one wasp, a
Crabro, too, with all the marks of conservatism about her, would take
such diverse things as bugs and flies, is almost too much to believe.
It is true that Crabro wesmæli is said to use both flies and bugs;[4]
but some accident may have led to this supposition, and stronger
evidence is needed to prove that there is variability in so deeply
seated an instinct.
[Illustration: CRABRO AND HER WHITE MOTHS]
The Crabro wasps all have pleasant ideas as to where they want to
live, but interruptus excels in the choice of a dwelling place. We
lately found ten or twelve of them in Milwaukee, nesting in an old log
on the shore of Lake Michigan, and when they opened their doors in
the morning they had before them the splendor of the great bay; but
calm in the midst of the glory they never paused on the threshold, as
Cerceris would have done, to take a look at the world before going to
work. One morning the earliest riser in our little colony was beginning
the day at half past nine. Of good size for a Crabro, with a square
determined–looking head and very direct and business–like manners, she
proceeded to cut out a new chamber for provisioning. These chambers are
nothing more than enlargements of the long gallery, such as are made
in stems by related species. At ten o’clock she departed on a hunting
excursion among the bushes on the bank above us, and came back in eight
minutes, carrying, much to our surprise, a white–winged moth, which
was clasped under the body by the second and third pairs of legs, and
was passed back to the third pair as she alighted before entering. A
moth is an innovation, a delicacy new to the accepted idea of what a
Crabro larder, accustomed to Diptera, should contain. A moment later
she was off again, but this time did not succeed so quickly, coming
back twice empty–handed for brief visits, and bringing in a load at
the end of half an hour. It took six moths to provision the cell, and
as the number neared completion her interest and energy seemed to wax
greater, the hunting intervals shortening to five, and even to two
minutes. We found afterwards that some of the moths were alive and some
dead, and that she packed them lengthwise, one after another, into the
closely fitting chamber. At a little before eleven o’clock the cell
was filled, and the wasp retired from sight, closing the door behind
her. We thought that she was resting, but presently the protrusion of
wood dust showed that she was enlarging her house, and an hour later
she came out and began to hunt again. By this time half a dozen were
working. Before leaving for the first time in the morning each one made
a thorough study of the place, and on returning they entered their own
doors, which were standing open, without hesitation, the long white
wings of the moths trailing behind them. Four species were represented
in the nests that we opened.
[Illustration: CRABRO STIRPICOLA]
Many species of Crabro make their nests in the stems of plants, and
among these is stirpicola, which is seen in numbers, through the middle
of July, flying about in a leisurely way, though it is only toward the
end of the month, or in the early days of August, that they settle
down to the work of making their homes. On the afternoon of July
twenty–seventh, after some very lively work in the heat of the day, we
walked down to the berry garden at half past five o’clock, rather to
rest ourselves than with the thought of undertaking anything new; but
a wasp–hunter cannot afford to choose his own hours, and we thankfully
accepted the sending of fortune when we came upon a stirpicola busy at
work in digging out her nest. She had only begun to excavate, and had
reached a length just equal to that of her own body. Her manners were
an agreeable contrast to those of the wasps that we had been watching
through the day. The feverish excitement of their ways seemed quite in
keeping with the burning heat of noon, while Crabro’s slow and gentle
movements harmonized perfectly with the long shadows of evening. To
fully appreciate the difference between Pompilus or Ammophila and
Crabro it is necessary to see them at work. The one is the embodiment
of all that is restless, vying with the humming–birds in swiftness and
energy, while the other is calm, quiet, and stately in all that she
does.
[Illustration: BOTTLE ON STEM TO MEASURE WORK OF CRABRO]
Some ten feet away was a second stirpicola, and this one, to judge
from the depth to which she had penetrated, must have been at work
for about two hours. We watched them both, and saw them bring up load
after load of pith. They bit out the pellets with their mandibles, and
passed them back between the legs and under the body until a quantity
had accumulated above the tip of the abdomen. They then walked backward
up the stem, and thus pushed out the mass as they came to the top.
Often they used the hind legs to assist in getting it out of the way,
sometimes kicking it to a little distance. Once in every two or three
trips they would come out far enough to expose part of the thorax.
They appeared and disappeared with the regularity of a machine, never
stopping to rest.
We remained with them until seven o’clock, when we placed a long bottle
over each stem in such a way that while it did not interfere with the
work of the wasp, it caught the chips of pith as they fell out. At the
end of an hour we noted the amount of accumulation in the tube, and
thus had a measure of their rate of work. The drawing gives an idea of
the arrangement of the tube on the stem. When we left them they were
still digging and delving.
At half past nine we took a lantern and went down to visit our charges.
We expected to find them at rest, and asleep; but on the contrary
they were working as busily as ever, and upon examining the measuring
glasses we found that they had not paused since we left them. We
measured the depth of the débris in the bottles, and then emptied them.
At four o’clock on the next morning we went to the garden, and
were much surprised to find that the two wasps had worked without
intermission throughout the night. Indeed they seemed to have shortened
a little the time that it took to make a round trip down the gallery
and up to the opening again, since there was more pith in the bottles
than we could have expected if they had worked at only their former
rate. Neither the coolness of the air nor the darkness of the night
had made the slightest difference to them. After watching them a few
minutes, and marveling at their powers of endurance, we cleared out the
tubes and returned to bed. At half past eight we found them still at
work. Unlike us, they had taken no morning nap, but had gone on with
their tunneling in their usual steady way.
From this time their ways diverged, and they must be described
separately. At nine o’clock the one that we had first seen came up to
the opening, walking head first, and flew off, remaining away seven
minutes. When she returned she at once resumed her work, and kept at
it without a pause until two in the afternoon. At this hour she went
away, and we never saw her again. We suppose that she was killed, for
it seems improbable that so faithful a creature could have deserted her
half–finished home. Pompilus quinquenotatus often deserted a partly
finished nest for some more enticing spot, and Sphex started several
excavations before making a final choice; but we cannot believe that
there was anything fickle about Crabro.
The second wasp came up head first to the entrance of her hole at
two minutes after nine, as though she had been influenced, in some
subtle way, by her neighbor’s example; but after looking about for a
moment she went back. She repeated this observation several times, and
finally, at twenty–five minutes after nine, came out and flew to a leaf
near by. Then she circled around, alighting a number of times, and at
last departed. Her stay was brief, for at just thirty–five minutes
after nine she returned, and at once settled down to her work.
We now began to make notes as to the length of time that it took her
to go down and bring back her load. We timed her again and again, and
found that she was remarkably regular, each of her trips occupying from
forty–five to fifty seconds.
All that day we kept her under strict surveillance, and never once did
she suspend her operations either for rest or refreshment. Late in the
afternoon, while we sat watching her as she appeared and disappeared
with almost the regularity of clockwork, we found it difficult to
realize that the patient little creature had been at work for more than
twenty–four hours, with only one brief intermission. Without hurry or
flurry she kept at her task, reminding us, in her business–like ways,
of the social wasps of the genus Vespa. When we left her, at dusk, we
attached the recording tube to the stem, and at ten o’clock in the
evening we found that she had not stopped working. We emptied the
glass, and left her.
At seven o’clock in the morning of July twenty–ninth we paid her a
visit, and could scarcely believe the testimony of our senses when we
saw that the record was one of unceasing toil through the long hours
of the second night. We began to wonder if she would ever finish her
task. Wonderful though she was, we had grown a little weary of our
long session of watching. We had been glad that she worked through the
first night; it was creditable to her and interesting to us, and we
admired her even more for sticking to it through the second, but when
it looked as though we might have to remain by her side through another
long day, watching an endless series of loads as they were carried out,
we confess that we thought she was rather overdoing it. Gradually,
however, she slowed up her work, taking two or three minutes to make a
journey down and up. At last, at just nine o’clock, her head appeared
at the top of the stalk, and after a slight hesitation she flew away.
The nest was completed.
We have studied wasps for a number of years, and we feel that we are
on terms of more or less intimacy with many of the species, but never
before have we known one to work after day was done. We have often
gone out with a lantern at bedtime for a tour of inspection among our
nests, and have always found the inhabitants quiet and presumably
asleep. The social wasps are very industrious, but during the hot
nights of July they are to be seen clustered together on the outside
of their paper nests in deep repose; and although the Vespa wasps
that nest in the ground sometimes come home late in the twilight, we
have never seen them work after it was really dark. Polistes fusca
may be said to share our cottage, so thickly does she hang her combs
under the shelter of our porches, and from observations taken at all
hours we know that she is quiet through the night. Sir John Lubbock, in
“Ants, Bees, and Wasps,” speaks of the great industry of wasps. He has
known them to work from early morning until dusk without any interval
for rest or refreshment; but here was our little Crabro toiling from
three in the afternoon of July twenty–seventh, through that night
and the day and night following until nine o’clock on the morning of
the twenty–ninth,—a period of forty–two consecutive hours with one
intermission of ten minutes on the morning of the twenty–eighth. Surely
she takes the palm for industry, not only from other wasps, but from
the ant and the bee as well.
[Illustration: NEST OF C. STIRPICOLA]
The nest was completed, but the work of storing it remained to be done.
The wasp flew away at nine o’clock, and ten minutes later came back
with something, we knew not what, for she dropped into her hole so
quickly that she was out of sight almost before we knew she was there.
Two minutes later she came up, and was off again. This time she was
gone twelve minutes, and when she returned we were again baffled in our
effort to see what she was carrying. When she came out she alighted
upon a leaf and attended to her toilet, cleaning both body and wings by
rubbing them off with her hind legs, and from this time on she never
started on a hunting expedition without paying this attention to her
personal appearance. On her third trip she was gone twenty minutes,
coming back with a small fly; and before we left her at ten o’clock,
she had stored six more. When we came back at half past two in the
afternoon she was working, and she kept up her goings and comings until
four o’clock, when she suspended operations for the day. On the next
morning we were called away, and know nothing of what she did, but on
the following day, Thursday, we resumed our observations. She worked
hard all the morning, but in the afternoon her trips were few, and were
made at long intervals. On Friday she worked from eight to nine, when
she departed, and never returned. We watched for her, at intervals,
all through that day and the next, when we were forced to conclude that
our faithful little worker had fallen a victim to some bird or beast.
We did not disturb the nest until four days later, when we cut the
stalk, and examined it.
We found that the tunnel was thirty–nine centimeters in length. This
was a long distance for her to excavate, and, all things considered,
her progress had been rapid. We have opened a number of stems that had
been stored by this species, and all the excavations were from thirty
to forty centimeters in length, the width of the gallery being about
three and one half millimeters, while on each side there was from one
to one and one half millimeters of pith that had not been cut away. Of
course these points varied with the diameter of the stem and also with
the size of the worker.
Our little stirpicola had stored one cell, had laid an egg, and had
built a partition of pith across the stem as a floor to the second
cell, before her untimely taking off. Had she lived, ten or twelve
cells would have been stored, one above the other. The completed cell
contained a larva and parts of eighteen flies of different sizes, four
species being represented. The flies had all been attacked by the
larva, the abdomens of some and the thoraces of others having been
eaten. The larva continued to eat for two days, and then spun its
cocoon. The flies found in this and in other nests of stirpicola were
all dead. All the pupæ that we kept wintered in the cocoon and came out
in the spring.
[Illustration: AMMOPHILA SLEEPING IN THE GRASS (AFTER BANKS)]
The females of Crabro, like those of other genera, seem to use their
galleries as sleeping places, but the males stop at any convenient
inn. We once entertained one of them for several nights in a hole in
one of the posts of our cottage porch. Other males, as in Philanthus,
spend time and care in digging a hole in the ground, to which they
return night after night. In Agenia the female keeps one cell ahead
of her needs, and tucks herself away in it very comfortably; but the
Pelopæi, instead of making this use of their tubes, congregate in the
evening where there are convenient crevices, and make as much fuss
about getting settled as a lot of English sparrows. Mr. Banks has
made a delightfully pretty as well as interesting observation on the
sleeping habits of Ammophila. In a corner of his garden where the grass
grew long, dozens of these wasps arrived every evening, and after a
good many changes in position, fell sound asleep, clinging to the stems
about one third of the way down. They registered at this hotel between
seven and eight o’clock, and departed before five in the morning. We
have seen a Pompilus take the greatest care in selecting a sheltered
spot under some leaves, where she afterward hung herself up, and
slept soundly until after eight the next day; and Mr. Brues has found
companies of Priononyx atrata passing the night on the stems of sweet
clover.