Lipoptena depressa, or the Western American deer ked, is a 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...

 from 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...

 Hippoboscidae

Hippoboscidae

Hippoboscidae, the louse flies or keds are obligate parasites of mammals and birds. In this family there are winged species which can fly at least reasonably well, as well as others with vestigial or no wings which are flightless and highly apomorphic...

. They are blood-feeding parasites of the mule deer

Mule Deer

The mule deer is a deer indigenous to western North America. The Mule Deer gets its name from its large mule-like ears. There are believed to be several subspecies, including the black-tailed deer...

 - Odocoileus hemionus in the western United States and Canada in the Rocky Mountains

Rocky Mountains

The Rocky Mountains are a major mountain range in western North America. The Rocky Mountains stretch more than from the northernmost part of British Columbia, in western Canada, to New Mexico, in the southwestern United States...

.

They are often misidentified as tick

Tick

Ticks are small arachnids in the order Ixodida, along with mites, constitute the subclass Acarina. Ticks are ectoparasites , living by hematophagy on the blood of mammals, birds, and sometimes reptiles and amphibians...

s.

The female fly will produce a single 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 at a time, retaining the larva internally until it is ready to pupa

Pupa

A pupa is the life stage of some insects undergoing transformation. The pupal stage is found only in holometabolous insects, those that undergo a complete metamorphosis, going through four life stages; embryo, larva, pupa and imago...

te. The larva feeds on the secretions of a milk gland in the uterus

Uterus

The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...

 of the female. After three larval instar

Instar

An instar is a developmental stage of arthropods, such as insects, between each molt , until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or assume a new form. Differences between instars can often be seen in altered body proportions, colors, patterns, or...

s, a white pre-pupa which immediately forms a hard dark puparium. The pupa is usually deposited where the deer slept overnight. When the pupa has completed its pupation. a winged adult emerges and flies in search of a suitable host, upon which fly sheds its wings and is permanently associated with the same host. This is typical of most members of the family Hippoboscidae.