Psychodids are about 5 mm long and usually the legs and wings are covered with fine setae. Some species may resemble moths by their small size, and the densely setose wings. The family is divided into two groups: moth flies and sand flies. Moth fly females are not blood-feeding, and have wings that are held roof-like over the body; the larvae are aquatic (Fig. 7.5g, h). Sand fly females are blood-feeders, and do not hold their wings roof-like. The larvae of sand flies are not aquatic. Larvae of both groups feed on decaying plant and animal material. Sand flies are found mainly in the tropics and subtropics, with a few species occurring in temperate regions in both the northern and southern hemisphere. The females have long mouthparts capable of puncturing skin and sucking vertebrate blood. The human-biting genera are Phlebotomus in the eastern hemisphere, and Lutzomyia in the western hemisphere. They are vectors of the protozoan parasites, Leishmania, which are the cause of leishmaniasis (kala-azar), and they vector a bacterium, Bartonella bacilliformis, which is the cause of bartonellosis (Oroya fever) and sand fly fever virus.

Moth flies have a cosmopolitan distribution. They are known as filter flies and sewer flies because they often breed in sewage treatment plants, and drain flies because they frequently occur in clogged drains indoors and sometimes outdoors. The domiciliary genera are Psychoda and Telmatoscopus. Psychoda species have the terminal antennal segments reduced in size, but Tel-matoscopus species do not. Species in these two genera occur as natural populations in urban and suburban environments. Moth flies are found in shady and undisturbed sites along stream banks, in wet decaying vegetation, bird nests, and tree holes.

Psychodids are commonly associated with the material in the filter beds of sewage treatment plants. The larvae feed upon the organic film that covers the surface of the filters. This film contains algae (Ulothrix), fungi (Phormidium), bacteria, and protozoans. The fly larvae are beneficial because they break down the gelatinous-like film that forms on the filter bed, and produce small fecal pellets that are easily carried away in the water that drains the filter beds. Adult moth flies can be serious pests when large numbers of them move to adjacentneighborhoods. They may be present year-round in buildings close to a sewage treatment facility. Live and dead adult moths may cause asthmatic reactions in people at the site or in other areas, such as around outdoor lights and doors where the adults aggregate, and their dead bodies collect.

Sewerfly, Clogmia albipunctatus (= Telmatoscopus) (Fig. 7.1k)

Adults are 4-5 mm long, and the thorax and abdomen are uniformly brown to grayish brown. Wings have two dark spots close to the base, and they have 8-9 white spots along the margin. Full-grown larvae are 8-10 mm long. The dorsal sclerites are dark brown to black; the posterior breathing tube is long and well sclerotized. This is a common insect in the filter beds of municipal sewage treatment plants, and in clogged drainpipes in residential buildings. In natural habitats, this species occurs along stream banks, in the mud of tree holes and rain barrels, and in wet and decaying leaves. It is widely distributed in the UK and northern Europe.

Filter fly, Psychoda albipennis Adults are about 1.2 mm long and the wings are uniformly gray and unmarked. The body is gray and distinctly hairy, and the antennae have 15 segments. Larvae are common in sewage treatment plants, in the filter beds, and on the bacterial film. They occur in decaying vegetation, and in septic drains. The adults feed on nectar and polluted water. This species is generally distributed throughout the UK and continental Europe.

Drain fly, Psychoda alternata Adults are about 2.5 mm long and the body is uniformly gray and covered with fine setae or hairs; antennae are 15-segmented. Full-grown larvae are 4.56 mm long and yellowish white to light brown. There are sclerotized areas on the dorsum ofall the larval segments. The head is dark brown and the terminal segment is sclerotized. Eggs are laid in batches of 20-100 directly on decaying substrates, such as the gelatinous-like surface that is in clogged drains or around fixtures in bathrooms and kitchens, and the surface of sewage disposal beds. Hatching occurs in about 48 h and larval development is complete in 9-15 days. The pupal period lasts 20-40 h. During warm weather and indoor conditions the life cycle takes 21-27 days to complete. There may be successive generations throughout the year, depending on the availability of a suitable substrate. The adults are weak flyers, and indoors they remain close to the breeding site, usually resting on walls in dark locations. They are attracted to lights at night. Outdoors, adults are found on foliage, usually in moist and shaded sites; they will feed on nectar and polluted water. It is common year-round, but may be more abundant when there is abundant food for the larvae. This species is generally distributed throughout North America, and it may occur in other regions.

Pacific drain fly, Psychoda pacifica Adults are 2-2.3 mm long and they have brownish-gray wings. This species is common in domestic habitats in the spring in western USA, and occurs from southern California to Alaska.

Other Psychoda The species that commonly occurs indoors along the Pacific coast, ranging from Alaska to southern California, is P. phalenoides. The adult is about 2 mm long, and has 13-segmented antennae and brownish-gray wings. There is a dense covering of setae on the wings and body. Adults of P. satchelli and P. cinerea are pale yellow and commonly found associated with the filter beds ofsewage treatment plants. P. satchelli has 14-segmented antennae, and P. cinerea has 16-segmented antennae. Both species are generally distributed throughout the USA. P. severini has also been recorded from sewage treatment plants. It is a parthenogenetic species and unmated females lay eggs directly on the filter beds.

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