Giant stag

The giant beetle (オオクワガタ, Ōkuwagata) is a rare insect found in every installment of the. It can be sold for 10,000 bells. It appears during the summer evenings, between the months of June and August, and between the times 11pm and 8am. It is extremely similar to the Stag Beetle, the only differences being that it is a bit darker and bigger.

In Wild World
Upon donating the Giant Beetle to the Museum, Blathers will comment:

"If you took this to a shop, they'd be willing to pay you quite well for it, I'm sure. That said, all it looks like to me is a glorified, expensive cockroach! Perhaps that's just me..."

In City Folk
Upon donation to the Museum, Blathers will say:

"The giant beetle boasts a massive horn, and yet it's said this bug is actually something of a milquetoast. Apparently this bug would prefer to stay inside where other creatures won't bother it. How precious. Even I could handle being near such a shy insect! I shan't be touching it, though... "

After donation, the giant beetle can be found on the top-most level of the insect section, three trees to the right of the lamp on the left-hand side, on the tree between the walkingstick and Bagworm tree and the Saw Stag Beetle tree.

In New Leaf
Upon donation to the museum, the giant stag can be found on a tree in the back of the upper right room of the insect section. The exhibit has this to say about the giant stag:
 * "Giant stags are huge stag beetles with one tooth in each side of their large jaws. They're very territorial but careful at the same time, so they usually hide in holes in trees. They have a long life span. Records show that some have lived up to five years. They're very popular among collectors as pets, so they commonly fetch a high price."

Encyclopedia Information
When the player has caught the giant beetle, they can find information about the insect in the bug menu. Below is the information regarding the giant beetle: