272 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1949 
harmonizes and blends with the surroundings or if the outline of the 
animal is obliterated by some type of camouflage. Most animals are 
so colored that they blend perfectly with their surroundings, some, 
such as the ptarmigan (Zagopus), certain hares (Lepus), and weasels 
or ermine (Mustela), even changing to white in winter to blend with 
the snow. 
Among insects, camouflage and mimicry have been developed to a 
high degree of perfection in many species. Some resemble their 
natural surroundings so closely that they are difficult to distingusih 
even though one is looking directly at them. Resemblance to dead 
or green leaves or stems is the most common camouflage, the pattern 
and form of the insect being modified to a strikingly perfect imitation 
of the color and form of those parts of the plant on which the insect 
usually lives. In the type of specialization known as mimicry, one 
species of insect very closely resembles and usually behaves like 
another which is distasteful or dangerous to animals. By this 
resemblance the imitator is often let alone by an anima) that mistakes 
it for the undesirable insect which it resembles. 
When it is not possible to avoid an enemy, some animals use @ more 
or less passive method which is well illustrated by the armadillos 
(Dasypus, Tolypeutes, and related genera) which roll themselves into 
a ball, completely protecting the feet, tail, and head within the armor 
plate of the body (pl. 6, figs. 1 and 2). This method effectively 
baffles many animals that would ordinarily devour them, and when 
the would-be attacker becomes discouraged and leaves, the armadillo 
unrolls itself and goes about its business. Another method is the 
feigning of death, which is well illustrated by the American opossum 
which, when alarmed, falls on its side with the mouth partially opened 
and appears so limp and inert that it is often left for dead by animals 
that would vigorously attack if they surmised the animal to be alive. 
Apparently opossums are unpalatable to many animals, so that this 
means of protection is very effective. When danger ceases to threaten, 
the opossum gradually resumes activity, but if the attacker is merely 
waiting nearby and makes a movement, the opossum will usually 
again go into its death-feigning act. It is supposed that this behavior 
is a type of fainting induced by fright and is perhaps not actually 
under the control of the animal. When the hog-nosed snake of the 
eastern United States, frequently called spreading adder (Heterodon), 
feels itself in danger, it feigns death, throws itself on its back, and 
assumes various grotesque poses if it is seriously aggravated. It does 
not, however, do this unless the annoyance is great and continued. 
Many insects feign death when a disturbance occurs in their vicinity. 
This is illustrated by the many beetles that inhabit low shrubbery, 
which drop from their elevated locations to the ground and remain 
quiet or quickly take refuge in a more protected location. 
