From Nookipedia, the Animal Crossing wiki
Fleas (ノミ, Nomi) are a rare insect, although worth only 70 Bells, in the Animal Crossing series that can be found from spring to early winter. In Animal Crossing: New Leaf, Fleas are more common than they are in the previous Animal Crossing games. They appear as black, hopping specks making bouncy noises on a random villager. When villagers have Fleas, their catchphrase includes their saying "itch". Fleas can be caught when players hit the villager with a net. Once the Flea has been caught, the villager that played host to it will give a response, usually one of denial, shock, or gratitude, which corresponds to their personality.
Donating to the museum
Blathers, the curator of the Museum, will unwillingly accept Fleas for exhibition. Here, he speaks of the Flea;
"Heed my words, (Player)! Bathe often! Wash yourself thoroughly! And shampoo regularly! Allow yourself to become filthy, and fleas move in! Blech! The very IDEA... Now I feel itchy."
The Flea can be found near the pond in the first room of the insect exhibit after donation.
Again, Blathers will express his disgust at the Flea in City Folk:
"Hoo now, have you ever had a chance to look at a flea up close and personal? They're utterly noisome! Especially vulgar are their flattened bodies, which allow them to wriggle into all sorts of places. Oh, mercy, I may need to sit on the floor for a moment. All this talk of fleas makes me feel rather woozy."
Once donated, Fleas appear as a barely-visible speck, bouncing around on the path on the central terrace in the insect exhibit.
The Flea can be found bouncing around on the upper-left room of the bug exhibit. The following description is given to them:
"Fleas are tiny insects that feed on blood from humans and animals, which then results in an itchy rash. They use their piercing mouths to suck blood and saliva at the same time. Unlike mosquitoes, both males and females suck blood. The females are larger than the males."
The human flea, Pulex irritans, is a widespread species of flea that is thought to have originated from South America. Despite the name, they are found on all manner of birds and mammals, including dogs, pigs, chickens, monkeys and even some species of bat. They have powerful legs that can be used to jump incredible heights: roughly 200 times their body length.
Fleas feed on blood. After feeding, females lay eggs on the skin or hair of the host animal. A single flea can have over 500 offspring in its lifetime, which live in the host's bedding feeding on dust and dried blood excreted by their parents after feeding.
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