Hello this is my bug guide, it may not be perfect but can still e a good source of information...
How to get the bug net:
In the south east corner of Mod Town, you will find A treehouse called Adam's treehouse, go inside and talk to adam, and he will give you the bug net.
How to sell bugs:
Go to Beryl's treehouse in swamptown, while inside equip the bug(s) you wish to sell, then tap the bug, she will ask you to sell... Also, if you talk to her, everyday, she ill have a different bug she needs, so Beryl will pay extra for it.
Bugs:
Monarch butterfly:
40 Gralats
Habitat: Anywhere
Size:85mm
Rarity: Fairly common
Dragonfly:
10 Gralats
Habitat: Swampy areas (Swamptown)
Size: 76mm
Rarity: Very common
Pillbug:
80 Gralats
Not much known about these... these are very rare and I caught two of them in Kris kill ems' bathrooms....
Emperor Butterfly:
40 Gralats
Habitat: Flying Anywhere
Size: 92mm
Rarity: Uncommon
Ladybug:
50 Gralats
Habitat: Around flowers
Size: 6mm
Rarity: Fairly common
Grasshopper:
20 Gralats
Habitat: Grassy areas
Size: 40mm
Rarity: Fairly common
Praying Mantis:
30 Gralats
Habitat: Around bushes
Size: 70mm
Rarity: Uncommon
Swallowtail Butterfly:
40 Gralats
Habitat: Flying anywhere
Size: 50 mm
Rarity: Fairly Common
Karner Butterfly:
40 Gralats
Habitat: Flying anywhere
Size: 70mm
Rarity: Fairly common
Firefly:
40 Gralats
Habitat: Dark areas/Woodlands (Lots in Onnet Forest)
Size: 16mm
Rarity: Fairly common
That is all, sorry I can't put in images of them all, I am limited to 5 images in a post