Ann Byers, age 11, of Milwaukee, Wisconsin, for her question:
Do butterflies have a sense of smell?
That papery white butterfly fluttering around the garden smells the nasturtiums while searching for something with a cabbage scent. The colorful butterfly perched on a daisy may be smelling the sweet fragrance of nectar. No butterfly has what we would call a nose. But she can smell and so can her first cousins, the moths. Some of these velvet winged insects can smell much, much better than we can.
We do not know everything about how it works, but the average butterfly certainly has a very keen sense of smell. The problem is bewildering because their sense organs do not resemble ours. What's more, they differ among themselves. And there are 14,000 different species of the Order Lepidoptera the scaly winged group that includes the butterflies and their kinfolk, the moths. Lastly, thousands of differently scented chemicals can be tested on each of these insects. So at present, we can report just a few of the details.
Our heads are big enough to house eyes and ears, noses and tongues with built in taste buds. But insects have small heads and their sense organs are strewn around on various parts of their bodies. Their sense organs may be fine hairs on the antennae or special cells in the legs or feet. They may be in the mouth parts or in various scales, pegs or pits on the body. In any case, an insect's sense of smell is closely related to taste, as ours is. Most of them can detect our four basic flavors sweet and sour, salty and bitter.
A cabbage butterfly can smell a cabbage from across several fields. She follows the scent at a leisurely pace of about 12 miles per hour, fluttering her papery wings about five times per second. She intends to lay her eggs on some plant of the cabbage family and its pungent odor guides her to the right spot. Her hungry grubs will dine on plants with this particular smell and taste and on nothing else. Nasturtiums have somewhat the same odor and sometimes both the mother and her grubs will settle for this food. The adult butterfly does not seek this tangy food for herself. If she eats at all, she sips the sweet nectar of various flowers. Many butterflies sample nectar with special smelling organs in their feet. The red admiral can sense sugar in a solution that is 200 times too weak for human taste buds.
At courting time, certain male moths are amazingly sensitive to the perfume of their lady loves. The glimmering green luna moth smells the scent of the female a mile away and flutters straight to her side. The male gypsy moth comes courting from maybe more than a mile, flying upwind with only the female's perfume to guide him. So far as we know, the champion is the male of the Chinese silkworm moth. The female secretes a yellowish greasy substance. To the human nose it smells faintly of leather. But neither the lady luna moth nor any other species can smell it at all. The male silkworm however, has been known to smell it and fly to her from a distance of seven miles.
The scent organs of insects are chemoreceptors that respond to odors of chemical molecules in the air. They may be hairs, pegs or scales poking through the insect's tough outer covering. When stimulated by this or that odor, they move this or that way and the information is relayed to nerves inside the body. The receptors may be almost anywhere, but moths and butterflies usually have plenty in their antennae.