432 ELEMENTARY ZOOLOGY 



familiar examples, each larva having a sharp horn on the 

 back of the next to last body-segment (fig. 164). When 

 disturbed the caterpillar assumes a threatening attitude, 

 and the horn seems to be an effective weapon of defence. 

 As a matter of fact it is not at all a weapon of defence, 

 being weak, not provided with poison, and altogether 

 harmless. 



But it would plainly be to the advantage of a defence- 

 less animal, one without poison-fangs or sting and without 

 an ill-tasting substance in its body, to be so marked and 

 shaped as to mimic some other specially defended or 

 inedible animal sufficiently to be mistaken for it and thus 

 to escape attack. Such cases have been noted, especially 

 among insects. This kind of protective resemblance may 

 be called mimicry. A most striking case is that presented 

 by the familiar monarch and viceroy butterflies (fig. 165). 

 The monarch (Anosia plexippus) is perhaps the most 

 abundant and widespread butterfly of our country. It is 

 a fact well known to entomologists that it is distasteful to 

 birds and is let alone by them. It is conspicuous, being 

 large and chiefly red-brown in color. The viceroy 

 (Basilarchia archippus), also red-brown and patterned 

 almost exactly like the monarch, is not, as its appearance 

 would seem to indicate, a very near relation of the latter, 

 but on the contrary it belongs to a genus of butterflies 

 all of which, except the viceroy and one other, are black 

 and white in color and of different pattern from the 

 monarch. The viceroy is not distasteful to birds, but by 

 its extraordinary simulation or mimicking of the monarch 

 it is not distinguished from it and so is not molested. In 

 the tropics there have been discovered numerous examples 

 of mimicry among insects. The members of two large 

 families of butterflies ^Danaidae and Heliconida?) are dis- 

 tasteful to birds and are mimicked by members of other 

 butterfly families .(especially the Pieridae). 



