Why does a spider sometimes make a close cobweb, and sit in the very
middle of its nest, and at other times leave its nest and start a new
spider-web?
The spider makes its cobweb according to the weather, both the present
and the future weather. Looking at a spider, you can tell what kind of
weather it is going to be: if it sits tightly in the middle of the
cobweb and does not come out, it means that it is going to rain. If it
leaves the nest and makes new cobwebs, it is going to clear off.
How can the spider know in advance what weather it is going to be?
The spider's senses are so fine that as soon as the moisture begins to
gather in the air,--though we do not yet feel it, and for us the weather
is clear,--for the spider it is already raining.
Just as a naked man will feel the moisture, when a man in his clothes
does not, so it is already raining for a spider, while for us it is only
getting ready to rain.