After you free Levias from Bilocyte’s harmful influence, Strich will find Bug Rock inside of the Thunderhead. Speak to him there to unlock Beedle’s Beetle Quest.
Talk to Beedle in his Airshop to learn that something is wrong; however, he does not want to talk about it now, so you should sleep in his bed and discuss it at night. Do as he says, and you will find out that both his Horned Colossus Beetle and the cage that it was kept in are gone. Agree to help him, then return to Skyloft in the Airshop.
Fly back to Bug Rock and speak with Strich who will tell you that he found a rare Horned Colossus Beetle. It must be Beedle’s! Once you tell him this, he agrees to give it back…if you can prove that you are a true bug lover by catching 10 bugs of his choice in 3 minutes.
Before taking on this challenge, you should make sure to have the Big Bug Net. With it, it is much easier to catch the bugs without them flying off. Also, it is likely that you will not be able to complete the challenge on your first try. Instead of focusing on winning, use a few attempts to develop a route and to learn the locations of the bugs.
Once you do finish the challenge, Strich will give you back the Horned Colossus Beetle. Return to Beedle’s Airshop. If you talk to him, he will once again tell you to wait until night to speak with him. Do as he asks, and he will be overjoyed about the return of his beetle. You will receive 5 Gratitude Crystals, as well as 50% off on your next purchase from his shop.