HOW INSECTS PROTECT THEMSELVES. 
523 
Finally, under our first category, we may include the very 
simple device of the insect which covers itself with its excrement or which 
carries with it a pile of its cast skins or the cast skins of its prey, or which 
encases itself in inedible and unpleasant material. The larvse of some 
Chrysomelidce are notorious for carrying their excrement; many Cassi- 
dides do this, having a special process to carry it on, and having the open¬ 
ing of the alimentary canal placed so far dorsally that the excrement can 
be retained ; the larva of Podontia does this, as do some Criocerides. The 
larva of the predaceous Chrysopa goes about carrying a pile of the sucked 
out skins of its victims (see fig. 76, page 154), while some Lepidopterous 
larvae wear their old cast skins (e.g., Roeselia fola which carries the cast 
head-cases) (fig. 301, page 436). It is probable that the case of the 
Psychid larva made of dry twigs or leaves is mainly protective in the sense 
that the bird does not care for the caterpillar with its outer case of dry 
material and so leaves it alone. The same is probably true of Caddis 
larvae (Trichoptera) which live in cases of small stones, shells and other 
indigestible materials. 
A number of species try to look distasteful; they may do this in 
two ways, by looking like some unpleasant object, by looking like some 
insect that is of itself unpleasant. Of the first, the most conspicuous 
are perhaps those insects which look like the droppings of birds; a good 
example is the young larva of Papilio demolius ; this starts life as an 
ordinary butterfly caterpillar of a dull brown colour; it soon becomes 
white over a large part of its body (fig. 292, page 422), and when not 
feeding, rests motionless on a leaf in the full view of all birds that pass; 
instead of hiding among the leaves, it conspicuously shows itself ; to us 
it is a very good imitation ; perhaps it is to a flying bird also. Another 
conspicuous example is the genus Tarache; the moth of T. notabilis is 
white with dull black markings ; instead of seeking shelter by day as 
most Noctuids do, it sits motionless on the top leaf of its foodplant, the 
wings closely applied to its body ; it has the shape and appearance of 
a bird’s excreta, and we believe it is sufficiently successful to escape its 
foe in that way. All the species of Tarache behave like this. 
We have referred above to the warning colouration of insects that 
are distasteful; but a very large class of insects that really are not 
distasteful adopt this colouring and pretend to be ; an example is figured 
in the family Zygcenidce. This mimicry of distasteful species may take 
two forms ; an insect will be found to very closely imitate another found 
in the same locality; or a whole number of insects in one place will be 
found to have a general scheme of warning colouring (e.g., black and 
yellow) part of them being really distasteful, part being mimics ; the 
birds may, if the former are sufficiently numerous, associate this colour¬ 
ing with unpleasant insects and so leave all alone ; one would imagine 
that the 6 frauds’ must add to the slaughter also of the genuinely distaste¬ 
ful ones, as if for instance, there were equal numbers of both, birds might 
go on trying for a long time and never be quite certain what they were 
