Two brightly colored butterflies have just flown by. They seems to be exactly alike, but actually one is a little larger than the other. The larger insect has a wingspread   of up to four inches. The smaller one has a wingspread of less than three inches and also a black line on its back wings. At first sight, it is hard to tell them apart. Would you guess from this that they are different-sized butterflies of the same species? Or that they are different species of butterflies but close relatives belonging to the same family? If you said yes to either question, you would be wrong, for these look-alikes belong to quite different families. The larger insect is the monarch butterfly  . As a baby insect, the monarch feeds on milkweed, which seems to give the monarch a disagreeable taste and smell. The bright coloring of the monarch acts as a warning sign to its enemy. Birds that eat butterflies soon recognize the monarch and quickly learn to leave it alone. The smaller insect is the viceroy  , which feeds on the leaves of trees. Birds would find this insect tasty, but because it looks like the monarch, birds keep away from it. The viceroy's similarity to the monarch gives it some protection from its enemies and helps it survive. There are other pairs of look-alike butterflies, bees and moths. In each case, one either has a disagreeable taste or smell, or can give a painful sting  . The larger is called the model. The insect that imitates   this model for protection is called the mimic. The bright coloring of the monarch butterflies is used to   _  .
catch other butterflies warn small insects express their ideas scare away the enemy