The Bug Net, also known as the Bug-Catching Net, in an obtainable item in A Link to the Past, A Link Between Worlds and in Skyward Sword. It can be used to catch all sorts of things, like fairies and Bugs.
A Link to the Past
There is a sick boy resting in the house just to the north of the Inn. This boy has a Bug-Catching Net which he will give to Link to use. In order to receive the Net from the boy, Link must have at least one Bottle in his possession."
"Link can use the Bug-Catching Net to capture a variety of flying creatures. Catch and release them or put them I an empty Bottle for future use."
Making a return from A Link to the Past, the Bug Net can be obtained yet again in Skyward Sword This nifty item allows Link to catch Blessed Butterflies and other insects, as long as Link approaches the Bug slowly. Otherwise, if Link flails it around, he will scare the creepy crawlers, and they will high-tail it out of that area. Any insect Link catches can be used to upgrade any potions he has.
Big Bug Net
Big Bug Net: Larger net for easier bug catching.
A Link Between Worlds
The Net is used once again to catch bees around Hyrule and Lorule. It is given to Link when he talks to the Bee Guy with a bottle somewhere in his inventory. It can be used to catch not just bees but other things such as Fairy's and Heart's. Completing the advanced course of Treacherous Tower twice upgrades the net into the Super Net. It can now deal eight times the damage turning the unassuming net into a well damaging weapon.