Where to Find and Catch Dewpider
From Pokemon Go Wiki
Dewpider are found and captured in Nest and Habitat locations.
Nests
Dewpider Nests are locations that consistently spawn Dewpider.
Habitats
Dewpider Habitats are spawn locations where Dewpider is likely to be encountered, but not guaranteed the way a Nest is.
Additional Tips and Information
Best Nests
If you know a really good nest or any of the nests above is really good, list them here: