SEVERAL LITTLE WASPS
In a search for the nest of one of our garden wasps we found, in the
woods beyond the fence, an old, weather–beaten stump which was riddled
with holes both large and small. The large ones were evidently the
passage–ways of ants, and were in constant use. The small ones seemed
to be uninhabited; but thinking they might contain the nests we were
in search of, and hoping that if we watched long enough we might see
our wasps flitting in and out, we settled ourselves close by. We
were resolved to stay as long as was necessary, and we blessed the
fate that made it our duty to sit on the grass under the shade of a
wide–spreading oak rather than in the distressing glare and heat of the
garden; for this was on the tenth of July, and the weather was what the
farmers call “seasonable.”
Twenty, thirty, forty minutes passed. Our eyes ached with persistent
gazing, and we had nearly made up our minds that the likely–looking
little holes were untenanted, when lo! a tiny wasp, carrying something
which we could not see distinctly, darted into one of them. It was
gone so quickly that we could not be sure that it was the species we
were looking for, and when it reappeared, after two or three minutes,
we saw that it was not. This point being determined, we watched the
hole with redoubled interest.
It was wearisome work, for the wasp stayed away a long time, and we
dared not let our gaze wander lest she should slip in without our
knowledge. At the end of thirty–five minutes she returned, but again
we failed to see what she carried. She flew with great rapidity, and
we scarcely caught sight of her before she vanished into her nest.
We could not but wonder at the ease and certainty with which she
recognized her own doorway among the hundreds of holes on the side of
the stump. This power of localization, while it is one of the most
common among wasps, is surely also one of the most remarkable.
Our little Rhopalum pedicellatum, for that proved to be her name, made
six more journeys within the next two hours. At the end of this time
we opened the tunnel, and, after a great deal of sawing and cutting,
succeeded in finding the nest five inches from the surface. It was
nothing but a slight enlargement of the gallery, in the soft decaying
wood. In it we found thirty–three gray gnats, all of them, except two,
being dead. On one of the dead ones was the egg, which had probably
been laid within a few hours.
The egg hatched two days later, on July twelfth, but on the fifteenth
the larva died. By this time many of the gnats looked very dry,
although we had tried to arrange for both moisture and ventilation by
packing the bottom of the tube with pith and covering the top with
muslin.
Further watching gave us one more wasp of this species, in the same
stump. This time the nest was only two inches from the surface. It
contained four dead gnats and two live ones, but no egg, showing that
the egg is not always laid on the first ones stored.
Much later in the season, toward the end of August, we found another
species of Rhopalum which proved to be new, and for which Mr. Ashmead
has proposed the name rubrocinctum, since it wears a red girdle around
the front end of the abdomen, being otherwise dressed in black like
pedicillatum. It makes its home in the stalks of raspberry bushes.
We opened a stem which contained thirteen compartments, separated by
partitions of pith. These were filled with black, gray, and green
gnats, which were packed in so closely that they were doubled over and
pressed out of shape. Each cell contained from twenty–five to thirty
gnats. In some of them were cocoons, in others larvæ, and in one was
an egg. The gnats were very carefully examined, and all of them, from
the cells that had been filled last as well as from those provisioned
earlier, were dead.
Other species of Rhopalum are said to prey upon spiders and aphides.
In studying the species that come in our way we are continually
developing distinct likings for some kinds above others. The appearance
of one of these favorites is always hailed with delight, and when the
season’s work is over we remember them with lively pleasure.
[Illustration: OXYBELUS QUADRINOTATUS]
It is thus, dear little Oxybelus, that we dwell upon the thought of you
and your pretty ways. No other wasp rose so early in the morning, no
other was so quick and tidy about her work, so apt and business–like
without any fuss or flurry. No other was more rapid and vigorous in
pursuit of her prey, and we think with admiration and gratitude of
the number of flies that you must have destroyed in the course of the
summer.
O. quadrinotatus is only one–quarter of an inch long, and is dark gray
with four whitish spots on the abdomen. It was before nine o’clock
in the morning that, while out on an early inspection tour in the
garden, we saw one of these wasps descend upon a sandy spot, and after
a moment’s rapid scratching with her first legs enter the hole that
she had opened. Under her body she was carrying a fly which looked
like the common domestic species. It was upside down, its head being
tightly clasped with the third pair of legs, and all of its abdomen
projected beyond the abdomen of the wasp. Ashmead quotes from Fabre the
remarkable statement that Oxybelus carries her flies home impaled on
her sting, an idea that probably arose from the fact that nearly the
whole body of the fly is visible.
Our new–found wasp stayed only a moment in her nest, although, as we
afterward found, it was long enough for her to lay her egg on the fly.
When she came out she quickly smoothed the sand over the spot with her
head and legs so that there was nothing to mark the nest, and flew
away. In three minutes she returned with another fly. She alighted two
or three inches away, and scratched for an instant, but quickly saw her
mistake, and found the right spot.
Again and again the pretty little worker went and came, while we sat
watching close by, admiring her deft handiwork in opening and closing
the nest and wondering at the ease with which she found it at each
return. There was nothing tiresome or dilatory about this species, and
within twenty minutes we had seen six flies stored up. The nest was
closed and the place smoothed over every time before she went away, but
when she entered she left the door open behind her. We once tried to
make her drop the fly, but when disturbed she flew up and alighted on a
plant near by, keeping her hold on it. The whole performance was brisk
and business–like, but without the feverish hurry of Ammophila and
Pompilus.
After the sixth fly was taken in we were afraid to let her go again,
thinking that the nest must now be completely provisioned, and that she
would not return. She was such a charming little wasp, scarcely bigger
than a fly herself and yet so useful in her industry, that we hated to
disturb her; but as we were obliged to have her for identification we
first caught her, and then opened the nest. It contained only the flies
that we had seen taken in, the egg being attached to the one lowest
down, on the left side, between the head and the thorax. It was long
and cylindrical. The flies were dead, but showed no marks of violence.
We learned later that it takes Oxybelus two hours to make her nest so
that this one must have been prepared the day before.
The egg, which was laid just before nine o’clock on the morning of
August seventh, hatched at a little after nine on the morning of August
eighth. The larva began to eat at once, and devoured all the inside
of the thorax and abdomen of the fly to which it was attached, in the
first twenty–four hours. On August twelfth it had reached the sixth
fly, and we supplied it with three more. On August fourteenth these
were gone, and we again replenished its larder, this time with two
flies. The larva had partly eaten these when something went wrong. Its
appetite failed, and on August sixteenth it died.
On further acquaintance this wasp lost none of her charm,—indeed, she
gained in interest from the almost human curiosity that she showed
about the affairs of other people. Where several were living close
together one of them would sometimes stop digging her own nest to perch
on a weed and watch the labor of another, and we once saw an especially
inquisitive character burrow through the closed door and enter the home
of her next–door neighbor.
[Illustration: NEST OF OXYBELUS]
We find but meagre notes on the genus Oxybelus. Ashmead says that
no observations have been made on the American species, but that in
Europe they are found to burrow in sand and to provision their nests
with dipterous insects. He says also that according to Verhoeff the
species in this genus do not paralyze their prey by stinging, as they
are unable to do so on account of the rigidity of the abdomen, but
that instead they crush the thorax with the mandibles just beneath
the wings, the centre of the nervous ganglia. He found in one nest
a dozen flies, and all had the thorax crushed and were dead. In the
case of our wasp we do not know how the flies were killed, but there
was no crushing of the thorax. The larva devoured, in all, ten flies.
At the time of its death it had probably finished the larval stage
of its existence, since nine days had elapsed since the hatching
of the egg. It may be that this period just before pupation is a
critical point in the life history of a wasp, for we lost several of
our nurslings at this time, and Fabre has noted that when, on account
of the presence of parasites, the larva of Bembex rostrata had lacked
something of its usual amount of nourishment, it perished miserably at
the end of its larval stage, not having strength enough to spin its
cocoon. No waspling in our charge ever died from lack of nourishment—on
that score our consciences are clear; but it was difficult to make
their conditions quite normal, and for this reason we may have been,
indirectly, the cause of their death.
The way in which our Oxybelus carries its prey is peculiar to itself.
Bembex and Philanthus also hold their prey under the body, but use the
second pair of legs, so that it does not project behind except at the
moment of entrance into the nest. Quadrinotatus, as we could distinctly
see, since she passed close to us several times in quick succession,
clasps the head of her victim in the third pair of legs, and flying
thus, with its whole body sticking out behind her, she certainly
presents a very remarkable appearance.
[Illustration: APORUS FASCIATUS]
Aporus fasciatus is a dark gray species, and is less than half an inch
in length. We were working one hot day in the melon field, when we
saw one of these little wasps going backward and dragging a female of
Mævia vittata which was much larger than she was herself. She twice
left it on the ground while she circled about for a moment, but soon
carried it up on to one of the large melon leaves, and left it there
while she made a long and careful study of the locality, skimming close
to the ground in and out among the vines; at length she went under a
leaf that lay close to the ground and began to dig. After her head
was well down in the ground we broke off the leaf that we might see
her method of work. She went on for ten minutes without noticing the
change, and then, without any circling, flew off to visit her spider.
When she tried to return to her hole it was evident that some landmark
was missing. Again and again she zigzagged from the spider to the
nesting–place, going by a regular path among the vines from leaf to
leaf and from blossom to blossom, but when she reached the spot she did
not recognize it. At last we laid the leaf back in its place over the
opening, when she at once went in and resumed her work, keeping at it
steadily for ten minutes longer. At this point she suddenly reversed
her operations and began to fill the hole that she had made, kicking
in the earth until the entrance was hidden. She then glanced at the
spider, selected a new place, and began to dig again. Surprisingly
large pellets of earth were carried out, backward, and loose dirt was
kicked under the body by the first legs. At the end of two or three
minutes she paused and remained perfectly still for a time, considering
the situation. Her conclusion was adverse to the locality, for she
soon filled in the hole, looked once more at the spider, and started a
third nest in a new place. This in turn was soon abandoned, as was also
a fourth. The fifth beginning was made under a leaf that lay close to
the ground, so that we could not see her at all. Fasciatus! had we had
the naming of her she should have gone down the ages as exasperans! We
had now watched her for an hour in the intense heat; the bell for the
noonday meal had sounded, hunger and thirst had descended upon us, and
most devoutly did we hope that she was suited at last, but no—after
twenty minutes’ work this place also was abandoned, and a sixth nest
started. This, however, was the final choice, and after forty–five
minutes spent in digging, it was completed. As the spider was brought
toward the nest it was left again and again while the nervous little
wasp flew to the hole, went in, examined, and came out again. At last
she backed in, caught the spider by the abdomen, and dragged it down.
It was too big—the head stuck in the hole; but she pulled from below
while we pushed gently from above, and it slowly disappeared. When she
came out we opened the nest and took the spider. The egg was fastened
to the middle of the left side of the abdomen. This one, as was also
the case with a second and third afterward taken from fasciatus, was
much less affected by the poison than is usual among the victims
of solitary wasps, moving from the time it was taken, without any
stimulation, and improving rapidly from day to day. Our second spider
appeared to be blind, and died upon the sixteenth day, while the third
had entirely recovered by the seventeenth day after it was stung, and
was released. Fasciatus, then, probably depends upon packing her victim
in tightly to keep it quiet.
It was three days and a half before the egg that we had taken hatched.
The larva developed rapidly, retaining its hold at the spot to which
the mother had fastened it. The spider remained alive for six days,
and the larva continued to grow for two days longer, when it died
also, being at the time about two thirds grown. We had great trouble in
protecting our growing larvæ from the inroads of fungi, and this was
one of the many that perished from that cause.
The next example of fasciatus that came under our notice was a
remarkable contrast to the one that we have just described, being as
slow and dignified as the other was nervous and hurried. She chose
a place and kept to it, her steady labor being interrupted only by
occasional visits to the spider; but it took her fifty minutes to
complete the nest. When finished it was a small gallery running down
obliquely for an inch and a half into the ground.
The only habit that this species can claim as peculiar to itself is the
strange and useless one of filling up the partly made nests that it is
about to abandon. We have never seen the sense of order carried to so
high a point in any other wasp.
[Illustration: WASP HOMES IN THE LOG CABIN]
On a hillside near our cottage stands a log cabin, deserted and
untenanted save for small creatures of the wild, which, though a
favorite spot with wood–boring wasps, is an unprofitable place for
study because of the difficulty of cutting out their nests without
destroying property. One day in early July, however, when we were
in the full fervor of hunting and longed to utilize every moment,
the wasps in our garden seemed to have resolved that enjoyment
and enjoyment only was their destined end and way, and became so
exasperatingly idle that in disgust we turned to the cabin. For half
an hour we saw nothing more exciting than a Trypoxylon immuring her
victims and a Pompilus hunting spiders under the eaves, but at the end
of that time Passolocus annulatus, a tiny wasp new to us, came flying
quietly along and entered one of the holes with which the ends of the
logs were riddled. She was carrying an aphis in her mandibles, and when
this was duly stored she reappeared and flew away. She had probably
just renewed her work after a spell of rest, since from this time on
for nearly an hour she came back regularly every four or five minutes.
She nearly always alighted on a blade of grass before going into the
nest, but did not appear to be malaxing her prey. Presently another
stage in the game was reached. She no longer brought aphides, but
little pellets of mud with which she plastered up the opening. After
she had finished this task and departed, we carefully chiseled into the
log and laid bare the nest. The tunnel ran in for about three inches,
and ended in three pockets which were well stocked with dead aphides,
there being fifty–seven in all. The innermost cell contained a larva,
and in the others were eggs, one of which hatched on the next day and
one on the day following. This second one was probably laid just before
the nest was sealed, giving forty hours for the egg stage; and it
proved to be the healthiest of the three. The others perished in early
infancy; but this one passed twelve days in eating, not only its own
share of provisions, but those destined for the other members of the
family as well, and then spun its cocoon.
We afterwards saw many of these wasps working in the logs of the cabin,
and noticed that they seemed to have seasons of leisure alternating
with spells of active work, as though when one cell had been filled up
and the egg laid they felt at liberty to amuse themselves for a time
before beginning on another. When an entirely new residence was to be
chosen they went house–hunting among the old holes in the logs; and
whether they had a high standard of sanitary conditions, or whether
they objected to making extensive repairs, a great many places were
examined and rejected before they settled down. The choice once made,
many loads of pith were carried out before the little householder was
satisfied. After the new abode was put to rights, the wasp would pass
a whole day in rest, spending much of the time in looking out of her
doorway and perhaps in observing the doings of her neighbors, but when
she began to work she was very industrious, and allowed nothing to
interfere with her labors, paying no more attention to us, no matter
how closely our curiosity led us to interrogate her, than if we had
been trees blown about by the wind.
[Illustration: NEST OF PERENNIS]
Some of the wasps dig deep into the stems of bushes to form galleries
for their nests, but we found one wise genus that went in only far
enough to make one or two cells, thus saving the trouble of carrying
her cuttings thirty or forty centimeters in direct opposition to the
force of gravity. This was Odynerus, whose nests we found in July, in
blackberry and raspberry stems. Our first species was perennis, whose
nests bear her mark in the shape of a pellet of earth placed above
each mud partition. One of her cells contained a wasp larva and about
sixteen caterpillars, nearly one third of which were dead, while the
rest were more or less lively. They seemed to have been stung near
the anterior part, as the last three or four segments were jerked up
violently when touched. The larva went on eating, and the caterpillars
went on dying from hour to hour. At the end of the eighth day, the baby
wasp finished its meal, having eaten all that had been provided for
it, as well as two dead caterpillars from another nest.
Much interest attaches to the way in which Odynerus lays her egg, since
instead of following the common fashion of fastening it to the prey she
suspends it by a tiny filament of web from the wall or ceiling of her
cell. Thus in O. reniformis, nesting in the ground, it is hung from
the ceiling, a mass of very imperfectly paralyzed caterpillars being
collected below, and when the larva comes out the thread lengthens
until the tiny jaws reach the food supply. Startle it ever so slightly
and the waspling retreats by way of its web, descending again only when
everything is quiet. For twenty–four hours it retains this path to
safety, and then, growing bold, it drops down and feeds at its ease.
We had opened hundreds of plant stems in quest of these suspended eggs
without being so fortunate as to find one, and were therefore much
pleased when our kind friend, Dr. Sigmund Graenicher, whose interest
in bees keeps him in touch with out–of–door happenings, and who has
given us much valuable help, brought us two stalks, one of which had
in it a nest of O. conformis, while the other contained two freshly
provisioned cells of O. anormis. In all three the egg had been hung
from the side of the cell about one third of the way down, and in
the nest of conformis, from which all but one of the caterpillars had
fallen, it hung loose against the wall. In the other nests the lower
part was packed tightly with sixteen small larvæ, upon which lay the
egg, supported in a horizontal position, although attached to the side
wall exactly as in conformis, and above were eight more caterpillars,
the whole forming a compact mass shut in by the usual partition of mud.
So closely were they crammed in that after counting them we were unable
to get them all back again, and although motionless in their narrow
quarters they became quite active when relieved from pressure. This
is an entirely different arrangement from that of O. reniformis, and
since the larva is in contact with the caterpillars from the moment of
hatching the manner of the egg–laying has no significance in relation
to the safety of the young.
[Illustration: NEST OF ANORMIS]
Conformis hatched on the morning after we received it, sloughing off
the skin of the egg, but remaining attached to it, and thus doubling
the length of the thread by which it hung. The caterpillar was slightly
separated from it, and it seemed to have no notion of feeling about
for its food, eating nothing for twenty–four hours, but growing and
developing nevertheless. We now piled up some caterpillars in contact
with it, and it began to eat, but after its own caterpillar and as many
as we dared take from anormis were gone it stubbornly refused to take
soft, tender little spiders, or caterpillars out of our garden; and it
perished, a victim to prejudice.
The two eggs of anormis were probably laid within a few hours of each
other, since they had both hatched on the morning of the third day,
and had broken from their attachment, beginning to eat at once. They
cocooned on the fifth day after hatching.
We had long wished to find a nest of O. capra, and early in September
fortune favored us. A neighbor of ours keeps a large tin horn hanging
under the porch. One day when she wished to use it, no amount of
blowing would bring forth a sound; and when she unscrewed the
mouthpiece to investigate the matter, out tumbled several small green
caterpillars and a quantity of dry mud. When we heard of this incident
we begged that if it should be repeated the nest and its contents
might be saved for us; and on the second of September we received the
mouthpiece of the horn with a message to the effect that a wasp had
been working at it for some days. Examination showed that there were
three cells, each containing a larva and a supply of caterpillars,
of which there were ten in the cell most lately formed, and only one
left uneaten in the oldest. The caterpillars, all of them being alive,
together with the wasp larvæ, were transferred to a place in which they
could be conveniently watched. None of the caterpillars died until
they were attacked. The larvæ ate all the food that was provided, the
oldest one cocooning on the fourth, and the second one on the seventh
of September. Of the third, we have no record, excepting that the
caterpillars had all been eaten on September eighth.
We happened to be passing through our neighbor’s grounds at nine
o’clock on the morning of September fifth, and calling to ask whether
there had been any more visits from the wasp, we learned that capra had
been seen making a mud partition in the horn on the day before. While
we were speaking she arrived and entered the mouthpiece, where she
remained for about ten minutes. When she departed we found that she had
laid her egg, which we carried away with us, wishing to determine the
length of the egg stage. This proved to be longer than that of any wasp
that we had heretofore known, for not until the morning of September
ninth did the larva make its appearance, the egg skin bursting and
leaving its tenant free to crawl away. In other genera the egg changes
into a larva imperceptibly, there being no sloughing off of the skin.
Capra, then, first finds a suitable crevice, and builds a partition
across the inner end, the earth being scratched up from some dry, bare
spot, and moistened in her mouth. Before gathering the ten or twelve
small caterpillars that are to provision the cell, she lays her egg;
and although we could not be sure, we thought that in this case as in
the others it was suspended.
Unless the cell is tightly packed at the beginning, capra certainly
needs the filament, for her caterpillars were so far from being
reduced to a state of decent immobility that we had to press wads of
cotton into the tubes in which they were kept to prevent them from
wriggling out of the way of the larva. None of our larvæ, not even the
one–day–old ones, were injured by their activity; but had the egg been
left to its fate among them it might have perished.
Later in September we found O. vagus bringing pellets from a
sharp–edged hole in the ground. Her method was to carry each load on
the wing to a distance of ten or twelve inches, where it was dropped
without the lively fling with which Ammophila discards her lump of
dirt. The red end of a match stuck into the ground two inches away
proved very disquieting to the dainty little wasp. These colored
matches were a great convenience in marking nests, and as we were
using them constantly, we did not guess, for a time, what the trouble
was. For half an hour she went and came, circling about, alighting
upon plants, and seeming entirely absorbed in examining them with
the minutest care, even alighting upon our hands with most engaging
friendliness, but pretending all the time that the nest was naught to
her. When the offending object was removed she hurried in at once and
resumed her work. The storing was not begun until the next morning,
when she took in six caterpillars of very different sizes, at intervals
of from ten to twenty minutes, and then filled the hole. We hoped to
find the little chamber arranged as in reniformis, but had not skill
enough to excavate in such a way as to show the internal plan. It is
remarkable that this genus, with only one set of tools for all its
species, has worked out such different styles of architecture, the
ground nests bearing no resemblance to those cut out of woody stalks;
and its flexibility is shown in the use of empty snail shells by a
foreign species, as well as by capra’s habit of partitioning off
convenient crevices found ready made.
The prettiest nests that we have seen in stems are those of Plenoculus
peckhamii, which separates its cells, not by solid partitions, but by
numerous granules of earth, which are used by the larvæ for forming
the case of the cocoon. One raspberry stalk that we opened had at the
bottom six of these mud cocoons, and above these three larvæ eating,
each in its own compartment, the provision in this case consisting
of immature bugs of the genus Pamera. Sometimes the stalk which is
being filled by Plenoculus attracts the fancy of a bee or of another
wasp, as is shown by the upper cells being filled by Osmia or Crabro,
or sometimes Plenoculus builds above the bee cells. When a number of
wasp eggs are placed in a plant stem, the last one laid is the first
to hatch. The different habits of the Hymenoptera in this respect are
very interesting. In the case of Ceratina dupla, the small carpenter
bee, the egg first laid hatches first, those above following in regular
order. The lower ones wait patiently in their cells until the one in
the top cell has matured, and then they all come out at once. When two
species occupy the same stalk, the lack of adjustment probably results
in the destruction of those lower down, excepting in the case of the
cuckoo flies, which have acquired the habit of gnawing their way out at
the side of the stem.