The subject of the relations and adaptations which exist between
flowers and insects does not appear to excite as much popular
attention as many other branches of natural science which are no more
interesting. Sprengel, Darwin, and Hermann Muller have been the chief
authors in giving us our present knowledge and interest in the study;
Sir John Lubbock has helped to popularize it, and Prof. W. Trelease
and others have carried on the work in this country.
The perforation as well as the fertilization of flowers has received
attention, but there is a wide field for further study for those who
have leisure to pursue it, as it requires much time and patience, as
well as closeness and accuracy of observation.
The accompanying figures, from drawings by Mr. C.E. Faxon, show a few
characteristic perforations and mutilations, and also represent two of
the principal kinds of insects which make them.
Any one interested in the subject will find an excellent brief review
of the work already done, a fair bibliography, and a list of
perforated flowers in Professor L.H. Pammel's paper on the
"Perforation of Flowers," in the _Transactions of the St. Louis
Academy of Science_, vol. v., pp. 246-277.
The general beauty of flowers is usually not greatly marred by the
perforations except in a few cases, as when the spurs of columbines
and corollas of trumpet creepers are much torn, which frequently
happens.
The great object of the perforations by insects is the obtaining of
the concealed nectar in an easy way. Very naturally, flowers which
depend on insect agency for fertilization rarely produce seed when
punctured if they are not also entered in the normal way. Perforating
is only practiced by a small number of species of insects, and many
but not all of the perforators do so because their tongues are too
short to reach the nectar by entering the flower. Some obtain nectar
from the same kind of flower both in the normal way and by
perforating.
The chief perforators of flowers, in this part of the continent at
least, appear to be some kinds of humble bees (Bombus) and carpenter
bees (Xylocopa). These insects have developed an unerring instinct as
to the proper point to perforate the corollas from the outside, in
order to readily get at the nectar. The holes made by the humble bees
and by the carpenter bees are usually quite different and easily
distinguished.
The humble bees have short, stout, blunt jaws, ill adapted for
cutting, and the perforations made by them are apparently always
irregular in shape, and have jagged edges. It has been stated that the
humble bees often bore through the tubes of their corollas with their
maxillæ, but in all cases observed by me the mandibles were first
brought into use in effecting an opening. The noise caused by the
tearing is often audible for a distance of several feet.
The true jaws of the carpenter bees are not any more prominent or
better adapted for making clean-cut perforations than those of the
humble bees; but behind the jaws there is a pair of long,
sharp-pointed, knife-like, jointed organs (maxillæ) which seem to be
exclusively used on all ordinary occasions in making perforations. The
inner edges of these maxillæ are nearly straight, and when brought
together they form a sharp-pointed, wedge-shaped, plow-like instrument
which makes a clean, narrow, longitudinal slit when it is inserted in
the flower and shoved forward. The slits made by it are often not
readily seen, because the elasticity of the tissues of some flowers
causes them to partially close again. When not in use the instrument
can be folded back, so that it is not conspicuous. The ordinary
observer usually sees no difference between the humble bees and the
carpenter bees, but they may be readily distinguished by a little
close observation.
[Illustration: THE PERFORATION OF FLOWERS.
1. Xylocopa and heads of male and female. 2. Bombus and head. 3.
Dicentra spectabilis, showing punctures. 4. Ribes aureum. 5. Ligustrum
Ibota. 6. Æsculus glabra. 7. Lonicera involucrata. 8. Caragana
arborescens. 9. Andromeda Japonica. 10. Buddleia Japonica. 11.
Mertensia Virginica. 12. Rhododendron arborescens. 13. Corydalis
bulbosa.]
No doubt, in some of the recorded cases of perforations, carpenter
bees have been mistaken for humble bees. The heads of all our Northern
humble bees are rather narrow, retreating from the antennæ toward the
sides, and with a more or less dense tuft of hair between the antennæ.
The abdomen, as well as the thorax, is always quite densely covered
with hair, which may be black or yellowish or in bands of either
color. With possibly one or two exceptions, the only species I have
seen doing the puncturing is Bombus affinis, Cresson.
The carpenter bees (Xylocopa Virginica) of this region have the head
very broad and square in front, and with no noticeable hair between
the antennæ. The heads of the male and female differ strikingly. In
the male the eyes are lighter colored and are hardly half as far apart
as in the female, and the lower part of the face is yellowish white.
The female has eyes smaller, darker, and very far apart, and the whole
face is perfectly black. The abdomen is broad, of a shining blue-black
color, very sparsely covered with black hairs, except on the first
large segment nearest the thorax. On this segment they are more dense
and of the same tawny color as those on the thorax. But it is
particularly from the character of the head that the amateur observer
of the perforators may soon learn to distinguish between a Xylocopa
and a Bombus as they work among the flowers. It is also interesting to
know that the Xylocopas are not so inclined to sting as the humble
bees, and the males, of course, being without stinging organs, may be
handled with impunity.
Among other insects, honey bees have been said to perforate flowers,
but authentic instances are rare of their doing much damage, or even
making holes. I have only recorded a single instance, and in this a
honey bee was seen to perforate the fragile spurs of Impatiens. When
searching for nectar they quite commonly use the perforations of other
insects. Wasps and other allied insects also perforate for nectar. My
only observations being a Vespa puncturing Cassandra calyculata, an
Andrena (?) perforating the spurs of Aguilegia, and Adynerus
foraminatus biting holes close to the base on the upper side of
rhododendron flowers. The holes made by some of the wasp-like insects
are often more or less circular and with clean-cut edges. The ravages
committed by larvæ, beetles and other insects in devouring flowers, or
parts of them, do not properly come under the head of perforations.
The question as to the cause of the handsome corollas of the trumpet
creeper (Tecoma radicans) being so often split and torn has been
accounted for in various ways in published notes on the subject.
Humming birds and ants have been blamed, the humming birds being such
constant visitors of these flowers that it really seemed as though
they must be the authors of the mischief. I have often watched them
when they appeared as though they were pecking at the blossoms, but
careful examinations, both before and after their visits, always
failed to show any trace of injury. Finally, on July 26, 1890, I was
rewarded by seeing a number of Baltimore orioles vigorously pecking at
and tearing open a lot of fresh blossoms, and this observation was
afterward repeated. That the oriole should do this was not surprising,
considering its known habits in relation to some other flowers. J.G.
JACK.
[Mr. Jack adds a list of sixteen plants whose flowers he has seen
punctured by the carpenter bee and seventeen others whose flowers were
punctured by the humble bee. He names more than thirty other flowers
which he has found perforated without having seen or identified the
authors of the mischief.--ED.]--_Garden and Forest_.
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