Where to Find and Catch Fomantis
From Pokemon Go Wiki
Fomantis are found and captured in Nest and Habitat locations.
Nests
Fomantis Nests are locations that consistently spawn Fomantis.
Habitats
Fomantis Habitats are spawn locations where Fomantis 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: