A botfly is any fly

Fly

True flies are insects of the order Diptera . They possess a pair of wings on the mesothorax and a pair of halteres, derived from the hind wings, on the metathorax...

 in the family

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 Oestridae, which includes all the members of the former families Cuterebridae, Gasterophilidae, and Hypodermatidae. It is the only family of flies whose larva

Larva

A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...

e live as obligate parasites within the bodies of mammal

Mammal

Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s, with the exception of a few screwworm flies in the family Calliphoridae. There are approximately 150 known species worldwide.

Dermatobia hominis, the human botfly, is the only species of botfly known to use humans as the host to its larvae.
Botflies deposit eggs on a host, or sometimes use an intermediate vector such as the common housefly

Housefly

The housefly , Musca domestica, is a fly of the suborder Cyclorrhapha...

, mosquitoes and even a species of tick (see Dermatobia hominis).