so that we can shave them
They're not whiskers, they're reinforced hairs similar to whiskers. Not only are the hairs located on their front legs, but also over their eyes.
cause you dont have a head
yes.
Yes.
diving beetle
yes they have tiny millimeter hairs on their legs.
yes. they hear by using the hairs on their legs.
Yep amount varies
They are like feelers on snails
hairs to grab uneven edges
The hairs on a spider's legs are used primarily to smell. Spiders don't have ears, noses or taste buds, so they rely on these hairs to sense their surroundings, if something is moving nearby, and if something is edible. These hairs are called thrichobotria.
The hairs on a housefly's legs and abdomen serve the same purpose as they do in humans. These hairs collect dirt and prevent them from getting inside the fly's body.