Notes on Defensive Scent Glands of Certain Coleoptera
International Journal of
Sce,t glands of Coleoptera
BY J. S. WADE 0
0 Scientific Assistant, Bureau of Entomology. Washington, ]). C , USA
The attention of the writer was first directed to the functions of defensive or repugnatorial scent glands in certain Coleoptera during the study some time ago of the biology of some of the more common species of Coleoptera bel,onging to the Tenebrionid tribe Eleodini, inhabiting portions of the central Great Plains region. Later, a growing interest led to closer field observation and to the examination, as opportunity offered, of' available literature on the subject. The notes which follow are intended merely to supplernent data already published, to which reference is made. It is ,obvious to anyone at all familiar with insect life, that the degree o sensitiveness and response in insects to. certain external phenomena is enormously greater than in vertebrates, and that their organs o sense are developed accordingly. It always has been a cause or wonder to. human beings as to the means by which the various lower animals recognize, distinguish and communicate with each other. Although we know very little about the senses oi the lower animals, it long has been know. that such senses as sight or touch are not nearly so important to insects as to We know that insects actually do distinguish and communicate with each other, or are attracted or repelled by each other, and as the neans of communication are not kn,own to use, may we not safely assume that such is brogh about through actors, the existence of which is not yet recognized or understood? Packard (1898) has called attention to the ease and rapidity with which exceedingly delicate, attenuated, and highly volatile odors unknown to us are perceptible to insects. McIndoo (1917) has suggested the presence of a chemical sense or senses, somewhat comparable to our olfact.ory sense, which receives and t,ransmits stimuli in a somewhat like that of odors, and has ably discussed the results of observations and experiments upon certain insects, and has give a short, historical review of the literature on the subject. In fact,
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[Oct.-Dec.
the subject as a whole in its relation to animal ecol,ogy makes a
powerful a.p.peal to the human imagination.
It has been well understood that the presence of defensive or
epugnatorial scent glands in certain insects exists in direct
adapration to the needs and habits of their owners and in close response
to their environment; also that such glands are of very frequent
occurrence and with much variation as to position, form, and
tunction; and that their presence is of value to the insect foc
repellent, defensive, and warning purposes. These eversible glands
most frequently occur in the form .of simple hypodermic pouches
from which can be emitted, when desired, varying amounts of an
odorous spray capable of permeating through.out considerable
surrounding atmosphere. Biologically speaking, the principle involved
in such cases, though often modified, is practically identical with
that of the mephitic, sulphuretted, oil-like fluid ejected by the
skunks. Thus far anal glands are known to be present in the
following families of Coleoptera Cicindelid, Carabide, Dytiscide,
Gyrinidle, Staphylinida?, Silphide, and Tenebrionid. The bl.ood itself
serves as a repellent fluid in the Meloide, and in the Coccinellid
and Lampyride, and it issues from a pore at the end o femur as
a yellowis?h fluid. The cantharidine in the blood of some species
of Meloid, commonly kn.own as "Spanish Fly," forms an
especially caustic protection against birds, predaceous insects and
reptiles. A number of the Carabide eject from. a pair of anal glands
a pungent, acid, and often corrosive fluid, staining the hands s
rust-red color, and in Galerita janus Fab., the "Bombardier
beetles" (Brach.inus), and others, it "explodes" or volatilizes, as
soon as it comes in contact with the air, and the discharge and
puff of vapor is accompanied ,by an audible report. This occurrence
may be repeated over and over again in succession at frequent
intervals. Westwood (1839) has recorded that specimens of a
Brachinus of large size from South America, when captured
"immediately began to play off their artillery, burning and staining
the flesh to such a degree that only a few specimens could be
captured with the naked hand, leaving a mark which remained for
a considerable time." The odor of rose or hyacinth given out by
certain Cicindelidm, or the fragrance exhaled by the European1
Aromia mosch.ata, are secretions probably formed by similar glands.
The larvae of certain Coleoptera, notably in the Chrysomelide, also
are supplied with eversible hypodermal glands of various kinds.
]olsom (1906) states that "the larvae of Melasoma lapponcum
evert numerous paired vesicles which emit a peculiar odor."
Packard has divided all scent-producing organs into repugnatorial
and alluring organs, and a third class including those for
recognition only, has been su (...truncated)