The Mimetic Power of Insects.
By Helen Montgomery
"WHY, Cousin Helen! What do you mean by saying that locust is a mimic?" asked my little cousins, John and Lincoln. "Yes, he is a very good mimic, and so are all the insects in this case. Look at them, and I will tell you in what way I have seen them mimic. "Insects have a power called 'mimetic,' which enables them to mimic, or imitate, the substances which afford them food and shelter. They are mimics all the way from the larva state to the imago, whether they are moths, butterflies, beetles, bugs, or locusts. In the larva state, some insects are easily distinguished from their food and shelter, but oftentimes they are not. Don't you remember how, when we went bug-hunting up in grandpa's orchard, we chased some white cabbage butterflies over the tomato bed, and you, John, found a brownish caterpillar on one of the plants? Then we hunted for more, and found one so much like the leaf in color that I almost took it in my hand before I saw what it really was. "When the insect is in its pupa state, it is as great a mimic as before; for then the cocoons and chrysalides, or aurelidæ, are of the same color as their hiding-places. The cocoons and chrysalides we find hidden under posts, fences, stones, hanging from trees, etc., are of the same color as the stones, bushes, etc. This light brownish cecropia cocoon is the color of the bush or tree on which it hung. Perhaps it was a barberry bush." "This one isn't brown; it's white," said Lincoln. "So it is. It came off the top of a white birch tree, and so it imitated the bark of that wood in color. I think that only in the imago state is the insect a mimic in shape. Examples of this kind are walking sticks and walking leaves. "One day I was out on a specimen hunt with a naturalist on the banks of Duck Pond, in Farmingham, Massachusetts. I was a short distance behind when I heard her call me; on my hastening to her she showed me what I thought was a little branch in a tin cup. Just as I was going to ask what there was curious or interesting about it, some little twigs on the side of the branch began to move, and I immediately thought it must be a walking stick, which I had read about, but never until then seen. I believe my friend said there were but three varieties of this insect in North America. "Any warm day in summer, when you boys are playing in the yard or orchard, you can see some very striking examples of this mimetic power; I mean locusts. These locusts on the upper row have wing-cases of a dusty color. I caught them one noon in the middle of North Street. When they were resting I could not tell the difference between them and the road; but as soon as they spread their wings, I could see and catch them." "Yes; that one I found in a marsh down at Ocean Park, where all the weeds and the soil were of a yellowish hue. Just look at the difference between this and the first one. This one has white wings, with a black line across them; the body is white, and the wing-cases look as if sand had been sprinkled over them. These came from the beach between Old Orchard and Ocean Park. If their wings were folded, it would be very difficult to distinguish them from the dry, white sand. I watched a long time one day to see if I could find any on the sand, and frequently I was astonished to have one fly up in my face when I had just looked carefully over the place where it had been lying. "Here is a Turner's butterfly. If sometime in spring you should see one of these on the ground, and not know what it was, you would be likely to say, as I did the first time I saw one, 'Oh, what a pretty leaf with black lines on it!' and you would be very much astonished, as I was, to see it fly away. "This Philodice butterfly is so yellow that if you were to see it on a dandelion you would be puzzled to know where the dandelion left off and the butterfly began, or vice versa. If a Vanessa Antiopa butterfly was on an apple tree (I have noticed they prefer russet apple trees), with its wings closed, I could not tell which was the bark or which the under side of the butterfly, were it not for a slow, waving motion of the wings, as if it were fanning itself. "One day, when I was hurrying up North Street, I saw, as I thought, a brown leaf drop down at my side from one of the trees. 'What a pretty leaf; oh!' and, running after a very pretty butterfly, I waited till it settled, put my hat over, and so caught it. Look at its under side, boys, and you will see that it might easily be mistaken for a leaf. "These purplish, clear-winged, day-flying humming-bird moths feed on the big thistle heads, and it requires 'seeing eyes' to discover them. "Beetles have this mimetic power to a great extent, but I have only a few to show you. This one looks like a little ball of dirt. Sometimes this kind of beetle is mistaken for a ball of dirt, and sometimes the dirt for the beetle. "I wonder if, when you have been eating blackberries, you have suddenly noticed a sharp, disagreeable taste in your mouth?" "I have," said John, "and a very disagreeable taste it was, too." "So have I," said Lincoln. "Well, perhaps you know, then, that you have eaten a blueberry bug. This is about the size, shape, and color of a green blueberry; and if you were eating your berries in the pasture, nothing would be more likely than that you should eat some bugs too. "I have only one more example of mimetic beetles here, and this is the painted clytus, which lives on the golden-rod. It is marked with green and yellow, thus mimicking the color of the flower. "Perhaps you are wondering why insects have this power? I think that the Creator gave it to them so they might escape from enemies that were not bright enough to see through it." —Helen Montgomery, in Christian Union.