It has been noticed that many dangerous and distasteful insects are rendered conspicuous by their brilliant colors, and examples of this so-called _warning coloration_ are not lacking among the butterflies. The Swallowtail caterpillars, which produce a very disagreeable odor, are usually marked by two great staring eye-spots on the back of the thorax. Some of the protected butterflies, such as the ill-smelling Zebra and Red Silverwing, are extraordinarily conspicuous by reason of striking color-combinations. Many entomologists believe that these peculiar color-schemes have been developed by protected butterflies as an advertisement of their inedible character. This view is not as popular as it used to be, but there may be something in it; it certainly seems to explain the structure and habits of some of the higher animals--the rattlesnake for example--better than any other hypothesis yet advanced. PROTECTIVE MIMICRY There seems to be a tendency among certain insects which are edible and unprotected, to bear a superficial resemblance to inedible or distasteful species. Thus certain harmless flies have developed a remarkable likeness to wasps and bumblebees, although in structure and habits they are really very different. Several diurnal moths, too, have transparent wings, and yellow bands about the body which give them the appearance of gigantic and singularly ferocious hornets. It is certainly a great advantage for a harmless insect to resemble some dangerous and inedible species, and the whole phenomenon of resemblance has been called _protective mimicry_. The best example of mimicry in American butterflies is the case of the Monarch (_Anosia plexippus_) and the Viceroy (_Basilarchia disippus_). The Monarch belongs to the subfamily _Euploeinae_, all the members of which are provided with secretions which render them distasteful to birds and predaceous insects. The Monarch advertises its inedibility by its bright brown and black wings, and its leisurely manner of flight. The Viceroy belongs to an altogether different group, the members of which are readily eaten by birds, and which do not resemble the Monarch either in form, coloration, or manner of flight. The Viceroy, however, has gradually developed so remarkable a resemblance to the Monarch that it is difficult to distinguish them at a little distance, although the Viceroy is much the smaller of the two, and has a traverse black band on the hind wing that is lacking in the Monarch. There is no doubt that the Viceroy benefits by this resemblance, as birds (doubtless mistaking it for the inedible Monarch) appear to give it a wide berth.