One of the first surveys of the bats in the Caverns discovered that the number seems to grow in the fall, indicating that the cave was used primarily as a home principally for hibernation during the winter. More recent observations indicate that, at the present time at least, the bats winter somewhere else and live in the cave only during the summer months, going elsewhere to spend the winter. Recently several thousand bats were banded by naturalists and of those which have been returned, one came from Jalisco, Mexico, some 800 miles south of the Caverns. If both observations were correct, and it may be assumed that they were, for both were made by naturalists, then the habits of the bats do change, but what prompts these changes is still a matter of speculation. Other matters of speculation are just how the bat flies so accurately in the dark, darting swiftly past innumerable objects yet never hitting one of them. Scientists call this phenomenon "echolocation," a sort of sonar principle by which the little mammals let out a high frequency squeak and judge the distance of objects by the time required for the echo to bounce back to their sensitive ears. Another mystery is how they find their way unerringly back to the cave, in the early morning as well as after a sojourn to some other area of the world, and how they know when the supply of food has increased to the point that it is sufficient for them to return. Visitors to the cave often wonder how the numbers can be estimated. 7,000,000 is a lot of bats. This has been reduced to a relatively simple calculation. Cavern authorities counted the number sleeping in one square foot of space, found between 250 and 300 could squeeze into the area. The number of square feet of ceiling space occupied by the sleeping creatures was then multiplied by the bats per square foot, and the estimate was reached. Life in the cave, it seems, has been governed by the bat, and even this little fellow can hardly be said to live there. Actually, he only sleeps there winters and during the day. He can't live in the cave all the time since there is no food there for him. Are there any living creatures that dwell in the cave all the time? Only those that can find food in the cave, and since the eternal darkness prohibits photosynthesis which is vital to all growing plants, other animals or insects would find a food supply almost practically nonexistent, at least any form of plant food. Yet there are cave crickets. One species was found which was entirely new to science, and they named it after the Caverns, calling the species _Ceutophilus carlsbadensis_. Their eyes do not seem to function, apparently depending upon their long antennæ to guide them. But what do they eat? The contents of their stomachs have revealed bits of insect remains which they have scavenged from the piles of guano. Thus the cave crickets depend upon the bat for their existence.