If the weather is likely to become rainy, windy or in other respects disagreeable, spiders fix the terminating filaments, on which the whole web is sustained, unusually short. If the terminating filaments are made uncommonly long, the weather will be serene, and continue so, at least for ten or twelve days. If spiders be totally indolent, rain generally succeeds; their activity during rain is certain proof that it will be of short duration, and followed by fair and constant weather. Spiders usually make some alteration in their webs every twenty-four hours; if these changes take place between the hours of six and seven in the evening, they indicate a clear and pleasant night.
The clouds grow heavier over head –
The spider strengtheneth his web.
~ Frank H. Stauffer, The Queer, the Quaint and the Quizzical, 1882