Numerous group of Lower Diptera are commonly referred to as crane flies, including the primitive crane flies (Tanyderidae), winter crane flies (Trichoceridae), phantom crane flies (Ptychopteridae), and the true crane flies (Tipuloidea). The application of the name crane fly refers to the common condition of elongate and often delicate legs. The true crane flies are grouped based on the possession of the following defining characteristics: adults with 1) throax with a V-shaped transverse mesonotal suture, 2) long deciduous legs that easily break at a suture located between the trochanter and femur, 3) ocelli lacking, 4) wing with two Anal veins (A1, A2) reaching the wing margin, and the larve being 5) metapneustic (rarely apneustic) with a 6) hemicephalic head capsule.
The classification of the true crane flies is problematic. They are currently defined under three different taxonomic criteria, as either Tipulidae, Tipulomorpha, or Tipuloidea. Crane flies are most commonly classified as a single family, Tipulidae (sensu stricto), including the subfamiles Cylindrotominae, Pediciinae, Limoniinae, and Tipulinae. The taxonomy utilized in this key classifies crane flies as the superfamily Tipuloidea (Oosterbroek and Theowald 1991) which essentially elevates all levels of classification one step (i.e, Limoniinae=Limoniidae; Limoniini=Limoniinae). A third classification is used that includes the Trichoceridae as a sister-group to the Tipuloidea, as the Tipulomorpha (Stary 1992). The use of this term is discouraged however because of the incongruence in larger scale phylogenetic studies as to the sister-group relationship between the Tipuloidea and Trichoceridae.
The biology of crane flies are diverse. The knowledge of species identity and distributions of species is largely known from the adult stage. The adult stage is how crane flies are most commonly encountered, however this stage is generally short lived. The true diversity of the group is seen in the lesser known larval stage of development. While only about 4% of species are associated with their larval stage, what is known about this stage of development displays a great diversity of larval habitat and feeding adaptations.