Psychodidae, also called drain flies, sink flies, filter flies,[2]sewer flies, or sewer gnats, is a family of true flies. Some genera have short, hairy bodies and wings, giving them a "furry" moth-like appearance, hence one of their common names, moth flies.[2] Members of the sub-family Phlebotominae, which are hematophagous (feed on blood), may be called sand flies in some countries, although this term is also used for other unrelated flies.
There are more than 2,600 described species worldwide, most of them native to the humid tropics. This makes them one of the most diverse families of their order.[3] Drain flies sometimes inhabit plumbing drains and sewage systems, where they are harmless, but may be a persistent annoyance.[4]
Live drain fly larvaeDatzia bispina holotype in Burmese amber
The larvae of the subfamilies Psychodinae, Sycoracinae and Horaiellinae live in aquatic to semi-terrestrial or sludge-based habitats, including bathroom sinks,[5] where they feed on bacteria and can become problematic. The larvae of the most commonly encountered species are nearly transparent with a non-retractable black head and can sometimes be seen moving along the moist edges of crevices in shower stalls or bathtubs or submerged in toilet water. The larval form of the fly is usually between 4 and 5mm (0.16 and 0.20in) long, and is shaped like a long, thin, somewhat flattened cylinder. The body lacks prolegs, but the body segments are divided into a series of rings called annuli (singular is annulus). Some of these rings will have characteristic plates on the dorsal side. The larval thorax is not significantly larger than the abdomen, giving the larvae a more "worm-like" appearance than those of most aquatic insects.
In some species, the larvae can secure themselves to surfaces of their environment using "attachment disks" on their ventral side. Like mosquito larvae, they cannot absorb oxygen through water, and instead breathe via a small dark tube (a spiracle) on their posterior end — they must regularly reach the surface to obtain oxygen. The larval stage lasts for between 9 and 15 days, depending on species, temperature, and environment. There are four instar stages.[4][6][7]
In small numbers, the larvae are sometimes considered beneficial, as their strong jaws can cut through the hair and sludge waste in drains which might otherwise form clogs. However, unless this sludge layer is removed entirely, the adult flies will continue to find it and lay more eggs.
While the biting midges also have larvae that have no prolegs and which also have attachment disks, the larvae of the netwinged midges can be distinguished from those of the moth fly by the multiple deep lateral constrictions of the latter.[6]
The pupal stage lasts between 20 and 40 hours. During this stage, the insect does not feed, but stays submerged near the water surface, still breathing through a spiracle, and soon metamorphoses into an adult fly, which bursts through a seam in the pupal casing and emerges onto the water's surface.
The adults are half as long as the larvae, but are much broader in appearance, with a pair of hairy wings held pitched-roof-like over the body. The wings have the most elementary venation of any of the Diptera, having little more than a series of parallel veins without crossveins.
The adults are typically nocturnal, though they orient themselves around lights and may appear to be attracted to light and odors. They are erratic fliers, and are often seen walking or running rapidly as well as taking flight.[8] They are most active at night, but may also be seen during daylight, or near windows, lights, or illuminated display panels.[9]
The adults live for about 20 days, during which they will breed only once, often within hours of emerging from their pupal casings. Females will lay their eggs (between 30 and 100) just above the water line inside moist drains. Within 48 hours these eggs hatch into drain worms, the larval form.[10]
Psychodidae SEM top view
Psychodidae SEM rear view
Psychodidae SEM view from left
high resolution SEM image of Psychodidae (drain- or moth flies), front view
high resolution SEM image of Psychodidae (drain- or moth flies) whiskers segments
high resolution SEM image of Psychodidae (drain- or moth flies) leg
The drain flies which are commonly found in bathrooms, Clogmia albipunctata, are not known to carry any human diseases, but have been known to be an opportunistic agent of myiasis. However, the subfamily of Phlebotominae does feed on blood with the ability to transmit (tropical) diseases, and Sycorax silacea can transmit microfilaria.[11] Inhalation of insect fragments may cause respiratory asthma.
Notofairchildia zelandiae (previously in Nemopalpus)Mandalayia beumersorum
This family has seven subfamilies that contain more than 2600 described species.[12][13]
Schulz-Stübner, Sebastian, et al. "Psychodidae (Drain Fly) Infestation in an Operating Room." Infection control and hospital epidemiology 36.3 (2015): 366-367.
Polseela, Raxsina; Wagner, Rüdiger; Kvifte, Gunnar Mikalsen; Rulik, Björn; Apiwathnasorn, Chamnarn (2018). "Revision of Bruchomyiinae (Diptera, Psychodidae) of the Oriental Region, with description of a new genus and species and discussion of putative male/female antagonistic coevolution". Insect Systematics & Evolution. 50 (1): 67–82. doi:10.1163/1876312X-00002183. S2CID91174059.
Galati, E.A.B. (1995). "Phylogenetic systematics of Phlebotominae (Diptera) with emphasis on American groups". Boletín de Dirección de Malariologia y Ssaneamiento Ambiental. 35 (Suplemento 1): 133–142.
Azar, D.; Nel, A.; Solignac, M.; Paicheler, J.-C.; Bouchet, F. (1999). "New genera and species of psychodoid flies from the Lower Cretaceous amber of Lebanon". Palaeontology. 42 (6): 1101–1136. Bibcode:1999Palgy..42.1101A. doi:10.1111/1475-4983.00112. S2CID84535813.
Barretto, M.P. (1962). "Novos subgeneros de Lutzomyia Franca, 1924 (Diptera, Psychodidae, subfamilia Phlebotominae)". Revista do Instituto de Medicina Tropical de São Paulo. 4: 91–100.
Poinar Jr, George. "Palaeomyia burmitis gen. n., sp. n.(Phlebotominidae: Diptera) a new genus of Cretaceous sandflies with evidence of blood sucking habits". Proceedings of the Entomological Society of Washington.
Mangabeira, O. (1941). "5a contribuição ao estudo dos Flebotomus. Viannamyia n. subg. (Diptera: Psychodidae)". Memórias do Instituto Oswaldo Cruz. 36 (251–262).
Quate, L.W. (1955). "A revision of the Psychodidae (Diptera) in America north of Mexico". University of California Publications in Entomology. 10: 103–273.
