Some species of crickets, too, and indeed many, many insects give forth odors from glands that exist just for that purpose.
No, indeed, these odors are not all alike. Some have a strangling quality like ammonia, and sometimes the odors are not disagreeable. Some insects have sweet odors, like perfumes.
The pleasant odors are not used to repel, but to attract.
If an insect wishes to see its mate, it may be able to give forth a pleasant odor that will reach a long way through the air, and the mate, smelling it, will follow it to its source. You see, this pleasant odor is one way of talking; at least it is one way of sending a message.
Insects can detect odors much better than we can.
No doubt many insects produce odors that affect other insects, but that are so faint we cannot smell them at all.
The sense of smell, even in the human being, is very wonderful. It is the keenest of all the senses.
You have studied weights and measures, and you know how small a quantity a grain of anything is. Well, you will be astonished to know that your nose can detect the presence of 1/2,760,000,000 of a grain of mercaptan, a substance having a very bad smell.
