Flightless Flies in Hawai‘i
by Neal L. Evenhuis, Senior Entomologist
Losing wings or having them reduced to thin strips or small pads is known throughout other winged insect groups, and it is thought that flightlessness evolved in relatively hostile environments: like high altitudes with strong winds where flying might get you caught in a strong wind and blow you away; or on small islands where flying is not necessary to find the resources you need to survive. Hawai‘i has both of these situations (high altitudes and small islands) and combining them probably had led to Hawai‘i having more than its fair share of flightless flies.
There are various types of wing reduction: aptery [total loss of wings or present as only a small nub, sometimes with bristles]; brachyptery [wings reduced in length and having venation, but not permitting flight]; stenoptery [wings reduced in width but only having a few veins]; and microptery [wing reduced to an appendage of varying shapes and lengths, but all without any trace of wing veins].
Two of the groups of flies in Hawai‘i where certain species have either lost or had their wings reduced include crane flies (3 species) and long-legged flies (9 species). In the crane flies, the flies are all apterous (loss of wings) and look somewhat like small spiders with long, gangly legs; while in the long-legged flies, the wing reduction is either by microptery or brachyptery.
One place where three species of flightless flies can been found is the boggy summit of Mt. Ka‘ala on O‘ahu. It is home to one species of flightless crane fly (Dicranomyia gloria) and two species of long-legged flies (Campsicnemus montgomeryi and Campsicnemus hao). The long-legged flies are found in the leaf litter under mossy Melicope (‘alani) bushes where they search for small invertebrates to prey on. They are extremely small and, because of their lack of wings, look almost like small ants. Their main food source are the small springtails (Collembola) or small larvae of other insects that roam around in the leaf litter.
Not having the ability to fly was not much of a problem for these endemic Hawaiian insects for untold millennia, but some have more recently succumbed to the introduction of predatory ants, which have ravaged the lowland forests of the islands, possibly leading to the extinction of many insect species. For a flightless fly that cannot quickly fly away and escape, a predatory ant could easily spell doom. On O‘ahu, the flightless crane flies and long-legged flies occur primarily at elevations above where ants are found and still exist, like on Mt Ka‘ala with an elevation of about 4,000 feet. But one flightless long-legged fly species that was described over 100 years ago (Campsicnemus mirabilis), occurred only at a low elevation of about 1,000 feet on Tantalus. It unfortunately has not been seen since its collection in 1901 and is feared extinct due to predation by the big-headed ant (Pheidole megacephala), populations of which on Tantalus increased to the point that they could be found roaming the forest floor wherever you looked.
However, hope springs eternal. A recent find of a new flightless long-legged species (Campsicnemus hao) in the Wai‘anae Mountains at an elevation of 1,500 feet, and in the midst of a large population of yellow crazy ants (Anoplolepis gracilipes), gives optimism that maybe flightless flies can actually survive the onslaught of invasive predatory ants and maybe they are just hunkering down in low numbers. We will keep looking for them!
With support from Hawaiʻi Tourism’s Aloha ʻĀina Program, Bishop Museum is updating their databases of ferns and flies as part of the project “Protecting Hawaiʻi’s Resources: The Story Our Data Can Tell.”