External parasites are more common in rabbits than internal ones and usually consist of fleas, ticks and ear mites. Regular grooming of your rabbit is important for a number of reasons, including the chance it gives you to check him for signs of external parasites.

Common external rabbit parasites:
Parasite Signs Effects Treatment
Fleas Scratching, brown specks on the skin Discomfort, excessive scratching leading to open wounds, excessive blood loss Regular grooming with fine-tooth comb to remove fleas and eggs, use of flea collar, flea sprays. More severe cases require bathing with flea shampoo or treatment by a veterinarian
Ticks Scratching; presence of tick is usually apparent on visual examination Excessive scratching, possible infection of open sores or transmission of diseases Regular grooming with fine-tooth comb to check for presence. Kill tick with tick spray or alcohol and carefully remove with tweezers. Extreme cases require tick dip or veterinary care
Ear mites Constant shaking of head or scratching of ears, presence of oily brown substance inside ears Discomfort, high risk of transmission to other animals, injuries to ears from scratching Refer to veterinarian for diagnosis; treat using bottled drops according to directions