BIOLOGY OF SATURNIID MOTHS—BLEST 453 
decrescens at rest shows a generalized resemblance to dead, brownish 
foliage. Tactile stimuli cause the moth to fly suddenly away, using 
the first depression stroke of its flight response to project it from the 
vertical substrate upon which it is resting. 
(2) The use of eyespot patterns. These, in the New World Hemi- 
leucinae, are exclusively borne on the hind wings. The moths when at 
rest show a generalized resemblance to dead and folded leaves. When 
the moths are touched lightly, the forewings are moved forward to 
expose the eyespots. The moth may also make a series of little “hops” 
by performing depression flicks of the wings. The stages in such a 
display performance are illustrated in plate 2, figures 1 and 2. 
These eyespot patterns appear to “parasitize” the inborn responses 
of small avian predators to their own enemies. It has been shown 
experimentally that the simultaneous presentation of an eyespot 
pattern with a prey object will inhibit or delay the feeding re- 
sponses of various small European passerines, and may even frighten 
them away (Blest, 1957a). This is not a very efficient form of pro- 
tective coloration, for the individual predators soon become habituated 
to the eyespots and learn to ignore them. 
(3) The acquisition of a nauseous taste or odor, coupled with an 
aposematic or “warning” display. Examples of these displays are 
shown in plate 5. Even within the Hemileucinae the nature of the 
nauseous material varies. Déirphia spp. possess an unpleasant, or, in 
the case of D. (Periphoba) spp., a foul odor, and nauseous body fluids 
and meconium. The advanced species of Hylesia are equipped with 
venomous hairs on the abdomen; so venomous, in fact, that in areas 
of Peru and Venezuela where certain species may, periodically, 
emerge in large numbers, there have been sporadic outbreaks of an 
eczematous skin condition caused by contact with the loose hairs. 
It has been shown that birds can learn to avoid prey objects after 
no more than one or a few encounters, if the prey is sufficiently 
nauseous (see reviews in Cott, 1940, and Blest, 1957b), and experi- 
ments on Barro Colorado have shown that marmosets learn with 
similar rapidity. This is an efficient mode of coloration, for, by the 
sacrifice of a relatively small proportion of the population, the ma- 
jority of the individuals are heavily protected. Generally, such 
species are equipped with conspicuous or gaudy coloration—striped 
or spotted patterns with a predominance of yellow, red, white, and 
black pigmentation; adaptively, this is certainly a device to improve 
the rapidity of the predators’ learning processes. 
Now, it is apparent that the efficiencies of these various protective 
devices are not equal. Habituation to eyespot patterns occurs rapidly ; 
one might be tempted to suppose that the interpolated hopping move- 
ments must necessarily increase the intimidating effect of the display 
but this is not so. While some individual birds may become so 
