Wolf teeth are vestigial teeth, which means that over the period of evolution they have lost their function, so, they are not actually necessary for the horse. They are usually quite small and are commonly found in the upper jaw, just in front of the first molar.
Not all horses or ponies develop wolf teeth, if they're going to they will start to erupt at around 6 months of age becoming fully visible by around 12 to 18 months. Some equines will lose their wolf teeth when they shed their temporary secondary molar at about 3 years of age.
Occasionally wolf teeth are present but do not erupt through the gum. they remain under the gingiva and are referred to as blind wolf teeth.
Wolf teeth do not cause a horse pain, however they can sometimes interfere with the bit so are often removed in a simple surgical procedure by an equine vet or dentist.
More on equine teeth: 10 signs that your horse needs a dentist ~ recognising equine dental problems