What type of external parasites are commonly found on animals?

The identification of fleas, ticks, mites, and mange as external parasites commonly found on animals highlights their role as ectoparasites that live on the outside of their hosts. Fleas are well-known for infesting pets like dogs and cats, causing discomfort and potential transmission of other diseases. Ticks not only feed on blood but can also transmit various infectious diseases, such as Lyme disease. Mites, which include species causing mange, can lead to significant skin issues in animals like intense itching, hair loss, and secondary infections.

In contrast, the other options identify different types of parasites. Worms, flukes, and protozoa are internal parasites that reside within the host's body, and viruses and bacteria represent pathogens that can cause diseases but are not classified as parasites in the same context. Insects, spiders, and arachnids encompass a broader category that could include both parasitic and non-parasitic species. Focused on external parasites, the correct answer specifically relates to those that impact an animal's surface and skin health, confirming its appropriateness in this context.