The genus Axarus is widely distributed with records from the Holarctic

Holarctic

The Holarctic ecozone refers to the habitats found throughout the northern continents of the world as a whole. This region is divided into the Palearctic, consisting of Northern Africa and all of Eurasia, with the exception of Southeast Asia and the Indian subcontinent, and the Nearctic,...

, the Neotropics and Australasia

Australasia

Australasia is a region of Oceania comprising Australia, New Zealand, the island of New Guinea, and neighbouring islands in the Pacific Ocean. The term was coined by Charles de Brosses in Histoire des navigations aux terres australes...

 . There are currently 5 described nearctic species . Erected as a subgenus (Anceus) of Xenochironomus , Axarus was subsequently renamed and elevated to generic status . The Connecticut River

Connecticut River

The Connecticut River is the largest and longest river in New England, and also an American Heritage River. It flows roughly south, starting from the Fourth Connecticut Lake in New Hampshire. After flowing through the remaining Connecticut Lakes and Lake Francis, it defines the border between the...

 in the eastern United States harbors locally dense populations of two Axarus species, both currently undescribed. These populations are interesting in that they are restricted to specific larval habitat (varve

Varve

A varve is an annual layer of sediment or sedimentary rock.The word 'varve' is derived from the Swedish word varv whose meanings and connotations include 'revolution', 'in layers', and 'circle'. The term first appeared as Hvarfig lera on the first map produced by the Geological Survey of Sweden in...

 clay and sometimes rotting wood) and thus there is genetic structure between populations in the river . The Connecticut River species are also notable in that they have extremely well developed polytene chromosome

Polytene chromosome

To increase cell volume, some specialized cells undergo repeated rounds of DNA replication without cell division , forming a giant polytene chromosome...

s and also maintain a high degree of inversion

Chromosomal inversion

An inversion is a chromosome rearrangement in which a segment of a chromosome is reversed end to end. An inversion occurs when a single chromosome undergoes breakage and rearrangement within itself. Inversions are of two types: paracentric and pericentric.Paracentric inversions do not include the...

 polymorphism

Polymorphism (biology)

Polymorphism in biology occurs when two or more clearly different phenotypes exist in the same population of a species — in other words, the occurrence of more than one form or morph...

 .

Species

• A. dorneri (Malloch
  John Russell Malloch
  John Russell Malloch was a Scottish entomologist who specialised in Diptera.In 1910 he emigrated to Urbana, Illinois, United States.-References:See...
  
  , 1915)
• A. festivus Say
  Thomas Say
  Thomas Say was an American naturalist, entomologist, malacologist, herpetologist and carcinologist. A taxonomist, he is often considered to be the father of descriptive entomology in the United States. He described more than 1,000 new species of beetles and over 400 species of insects of other...
  
  , 1823
• A. rogersi (Beck and Beck, 1958)
• A. scopula (Townes, 1945)
• A. taenionotus (Say
  Thomas Say
  Thomas Say was an American naturalist, entomologist, malacologist, herpetologist and carcinologist. A taxonomist, he is often considered to be the father of descriptive entomology in the United States. He described more than 1,000 new species of beetles and over 400 species of insects of other...
  
  , 1829)