From Nookipedia, the Animal Crossing wiki
Dung beetles (フンコロガシ, Funkorokashi) in the Animal Crossing series are an unspecified species of dung beetle that can only be caught when snow settles in the winter, from early December to late February. They roll snowballs around town, a substitution for the balls of dung that their real-life counterparts roll. They can be sold for 800 Bells. Dung beetles fly away when approached. In Doubutsu no Mori e+, they will roll balls of any kind around town.
Upon donation to the museum
In Wild World
"I say, I've actually heard it said that their dung-rolling is considered endearing! Absolute rubbish. It is a dirty habit. Dung is dirty. There is no refuting it! Hoo... What a world..."
In City Folk
"These beetles are also known as scarabs and were once revered in some parts of the world. Looking at it now, I must admit there IS something a bit refined about its antennae and legs..." —Blathers
After donation, the dung beetle can be found rolling a piece of dung in the lower terrace in the smaller dirt circle, sharing the exhibit with the migratory locust.
In New Leaf
Since Blathers does not talk about the bug, the exhibit provides the information as follows:
"Dung beetles are famous for the exact thing you'd assume they're famous for. In fact, they use their namesake both as a source of food and a place to lay their eggs. Dung beetles are very strong and can roll things 10 times the weight of their bodies. One species can even pull objects 1,141 times its weight, which is like a human pulling 6 packed buses!"
Members of the insect family Scarabaeidae feed almost exclusively on feces and decaying matter. Many species have a good sense of smell. Dung beetles lay their eggs in dung. There are around 30,000 species of scarabaeidae worldwide.