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Psychodidae

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Psychodidae is a diverse family of true flies found throughout the world. They are known by many common names, including drain flies, sink flies, and sewer gnats. Some people call them moth flies because of their short, hairy bodies and wings. This fuzzy appearance makes them look similar to tiny moths. There are more than 2,600 described species in this family. Most of these species live in humid, tropical environments.

Notofairchildia zelandiae
Notofairchildia zelandiae

The life cycle of these flies involves several distinct stages. It begins when a female lays between 30 and 100 eggs. She typically places these eggs just above the water line in moist drains. Within 48 hours, the eggs hatch into larvae, which are often called drain worms. The larval stage lasts between 9 and 15 days, depending on the species and the temperature. These larvae are nearly transparent, shaped like thin cylinders, and possess a non-retractable black head. They live in aquatic or sludge-based habitats, such as bathroom sinks or sewage systems.

Datzia bispina Fig1 A
Datzia bispina Fig1 A

Because they live in wet environments, the larvae have specialized breathing mechanisms. They cannot absorb oxygen directly from the water like some other aquatic insects. Instead, they breathe through a small, dark tube called a spiracle located on their posterior end. This means they must regularly reach the water surface to obtain oxygen. Some species use attachment disks on their ventral side to secure themselves to surfaces. The larval body is divided into segments called annuli, which are rings around the body. While many find them annoying, the larvae can be beneficial by eating bacteria and sludge. Their strong jaws can even help cut through hair and waste that might cause clogs.

Protopsychodinae Fig1 A Mandalayia beumersorum
Protopsychodinae Fig1 A Mandalayia beumersorum

After the larval stage, the insect enters the pupal stage. This stage lasts between 20 and 40 hours. During this time, the insect does not eat. It remains submerged near the water surface, still breathing through its spiracle. Eventually, the insect undergoes metamorphosis to become an adult. The adult fly emerges by bursting through a seam in its pupal casing. Once on the surface, the adult fly is much broader than the larva. It holds its hairy wings in a shape that looks like a pitched roof. These wings have very simple venation, consisting mostly of parallel veins without crossveins.

Adult Psychodidae are typically nocturnal, meaning they are most active at night. They are erratic fliers, moving in shaky or unpredictable patterns. They are often attracted to lights and certain odors. Some adults can also be seen running rapidly across surfaces during the day. An adult fly typically lives for about 20 days. Most adults will breed only once in their lifetime. This breeding often occurs within just a few hours of emerging from the pupal stage.

Datzia bispina Fig1 A
Datzia bispina Fig1 A

While many drain flies are harmless, some members of the family are more significant to human health. The subfamily Phlebotominae is hematophagous, which means they feed on blood. In some countries, these are called sand flies. While the term sand fly is also used for other insects like horse flies, these specific Psychodidae can transmit diseases. For example, the species Sycorax silacea can transmit microfilaria. Other species, like Clogmia albipunctata, are not known to carry human diseases, though they can be a nuisance. In some cases, inhaling insect fragments may cause asthma.

Scientists have discovered that this family has a very long history on Earth. We know this through fossils preserved in various types of amber. For instance, species like Datzia bispina are found in Burmese amber from the Late Cretaceous period. Other fossils, such as those in Baltic amber, date back to the Eocene epoch. We also find specimens in Lebanese amber from the Barremian age of the Early Cretaceous. These ancient remains show that the diverse lineages of Psychodidae have existed for millions of years.

Notofairchildia zelandiae
Notofairchildia zelandiae
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Drain fly larvae.ogg
File:Datzia bispina Fig1 A.jpg
Datzia bispina Fig1 A.jpg
File:Notofairchildia zelandiae.jpg
Notofairchildia zelandiae.jpg
File:Protopsychodinae Fig1 A Mandalayia beumersorum.jpg
Protopsychodinae Fig1 A Mandalayia beumersorum.jpg
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