Hoo my! Many thanks for donating such a valuable insect, wot wot! This scarab beetle is as valuable as its weight in purest platinum! Disgusted I may be, but I shan't turn down such a pricey donation! Cheers!"
Once donated, the scarab beetle can be found on the top of of a cedar tree. It is directly below the cedar tree furthest to the left when using the northern entrance to the second room.
In City Folk
"From the gorgeous to the grotesque, the fruit-beetle family has a wide variety of members, indeed... Among them, the shiniest by far is the scarab beetle. Not that it makes any bit of difference to me. If it has antennae, it's most unconscionably vile..."
It can be found on the top terrace of the bug exhibit, on the second cedar tree from the right - sharing it with the Fruit Beetle.
In New Leaf
Blathers will no longer give a description upon receiving the bug, but the museum description is as follows:
"Scarab beetles have elegant, metallic-looking bodies and are shinier even than fruit beetles. They're so shiny that they're said to gleam like gold. They're very rare and can be sold for high prices. Like all beetles in the scarab family, the outer shell provides a very thick layer of protection from predators. The high value and golden shell do make them more vulnerable when it comes to Bell hunters, though."
The scarab beetle is found in the northeast room of the bug exhibit, sharing a tree with the Jewel Beetle in the far right corner.