522 
LEPIDOPTERA. 
Cimicidce in a strong degree; Myrmeleo, Ascalaphus , Chrysopa and 
some other Hemerobiidce exhibit the same phenomenon ; and a number 
of beetles, notably perhaps the Carabidce, some Cerambycidce and some 
Cicindelidce can be added. 
We cannot clearly separate the production of scent from the produc¬ 
tion of oil or fluid, having not only a scent but either a bad taste or some 
caustic property. Many Coccinellidce excrete such oils as notably do 
the Cantharidce; Elays and other large Tenebrionidoe, Autarches and 
Pcecilocera among Acridiidce, are also conspicuous examples, and it is 
reasonable to conclude that the effect of this secretion of fluid is quick 
in effect, the bird or beetle seizing such an insect promptly getting the 
taste or caustic result of the oil and dropping its prey at once. In the 
case of Autarches and of several of the Chalcosiine division of Zygaenids, 
e.g. (Campylotes ), the fluid is not only secreted but bubbles out at the 
orifice, forming a mass of bubbles similar to that produced by Cercopidce ; 
the curiously sudden way in which this happens is very striking, not to 
say alarming. A number of insects which do not produce scent or oil 
are apparently distasteful on account of the presence in their tissues 
of distasteful substances, either due to the secretion of some constituent 
for this purpose or due to the food they take in ; the Danaides are ex¬ 
amples of such insects as are also the Coccinellides and Cantharides. In 
the majority of these cases we find that with distastefulness is combined 
a system of warning colouration which advertises the fact, or which is 
sufficiently vivid to be associated with the distastefulness in the mind of 
the predator. That is, most distasteful insects are “ warningly colour¬ 
ed,” so as to secure the maximum protection from their distastefulness 
by plainly indicating that they are distasteful. We are not here dis¬ 
cussing colouration, but we shall have need to refer to this fact again. 
The number of groups in which warning colouring occurs is very large. 
A rather doubtful device is the extremely hard and thick integument 
of some insects, beetles especially, often combined with horns, spines or 
other projections calculated to be troublesome to the consumer. It is 
difficult to find any other value in the intensely thick hard portions of 
the integument of some beetles, as also in the hard knobs and spines of 
many Pentatomidce, for instance, and we may conjecture that the posses¬ 
sion of such an integument does turn the scale in favour of the possessor 
and against some unarmed insect equally available at the moment. 
Another device is to be found in the hairiness of so many caterpillars; 
there is good ground to believe that a hairy caterpillar is not as palatable 
to a bird, for instance, as is a smooth hairless one, and when we consider 
how indigestible chitin is and how much room the hairs take up, we can 
imagine why. This device is carried to an extreme when the hairs them¬ 
selves are poisonous as is often the case ; hairy caterpillars occur prin¬ 
cipally in the Lymantriidce, Lasiocampidce, Eupterotidce, Limacodidce and 
Arctiidce ; those with poisoned hairs chiefly in the two former rarely in 
the last. 
