My opinion: long mammals like cows, horses, camels, etc can't reach their behinds with their limbs. They can use their head (especially when the tail doesn't reach the fronter part of the behind), but it's not efficient because their head is heavy (and they're heavy animals in general) and has more inertia. Therefore, a tail is their swift efficient defense for the behind.
By contrast, smaller mammals like cats, dogs, rats, etc, don't use their tails to deter insect, because they can easily jump, move quickly, or smash their head into their body, because they are much lighter.
Now, this makes me wonder, why do cats and dogs have tails. Maybe im the case of cats it is for equilibrium, but dogs? I think dogs use tails to show people when they're excited :)
By contrast, smaller mammals like cats, dogs, rats, etc, don't use their tails to deter insect, because they can easily jump, move quickly, or smash their head into their body, because they are much lighter.
Now, this makes me wonder, why do cats and dogs have tails. Maybe im the case of cats it is for equilibrium, but dogs? I think dogs use tails to show people when they're excited :)