Re: Which came first, the insect or the spider?

Early arachnids (scorpions) may have come first (in the Silurian-440 
million years ago), but true spiders and insects appeared later- around 
the same time in the Devonian (>400 million years ago).  Primitive insects 
could not fly and insect wings seem to have evolved in the Carboniferous, 
before 350 million years ago.

References:

Borror, D. J., C. A. Triplehorn, and N. F. Johnson. 1989. An Introduction 
to the Study of Insects, 6th ed. Saunders College Publishing, Fort Worth.

Foelix, R. F. 1996.  Biology of Spiders, 2nd ed. Oxford University Press, 
New York.