The Bug Medal is a must-have for bug fans. So long as this medal is in your pouch, you can view possible locations of bugs on your map. Keep in mind that you won’t always find bugs there though.
Bugs are useful for infusing potions. Plus they’re fun to collect. Besides that though, the Bug Medal isn’t a necessity, but more of a luxury (and a rather expensive luxury too!).
Where to Find
However it’s not cheap–it’ll set you back a whopping 1,000 Rupees. If you’re not in a hurry, you can get it for half price by completing Beedle’s sidequest (available after the 6th dungeon).