The true flies are insects, scientifically known as Diptera which means two winged species.
This large group consists of around 120,000 species worldwide but it is believed that more of the same amount are still not described. It is one of the major insect orders in terms of both ecological and human (medical and economic) importance. While the majority is beneficial and of great importance to their local ecosystems only a dozen or so species are associated with human habitations while about a handful species are well known as pests. It is yet unknown how many species exist in the Maltese Islands as new species are found frequently but a very rough estimate from local literature indicates that till 1995 over 218 species were already known locally. Others have been recorded since. These endemic species include the Schembri’s Spider Fly (Ogcodes schembrii) Dubbiena tal-Brimb ta’ Schembri.
Flies are well adapted for aerial movement, and typically have short and streamlined bodies. They have a mobile head with eyes, and, in most cases, have large compound eyes on the sides of the head, with five small ocelli on the top area. The antennae take a variety of forms, but are often short, to reduce drag while flying. Flies consume only liquid food, and their mouthparts and digestive tract show various modifications for this diet. The majority of species spit out saliva on solid foods to predigest it, and then suck the external semi-digested material back in. They also regurgitate partly digested matter and pass it again to the abdomen. The most apparently primitive flies have piercing blade-like mandibles and fleshy palps, but these have developed into numerous different adaptive forms in different groups. These include both the fine stilleto-like sucking mouthparts of mosquitoes, and the fleshy proboscis of houseflies. The gut typically includes large diverticulae (outpouchings of a hollow or a fluid filled structure) allowing the insect to store small quantities of liquid after a meal.
The female lays her eggs as close to the food source as possible and development is generally rapid, allowing the larva to consume as much food as possible in a short period of time before transforming into the adult. In extreme cases, the eggs hatch immediately after being laid, while a few flies are ovoviviparous, (bear live young) with the larva hatching inside the mother
Species like the House, Blue, Green and Flesh flies can be very loyal to our establishments and these are the ones that should be treated as pests. As a world wide perspective Diptera, in particular the mosquitoes (Culicidae), are of great importance in disease transmitters, acting as vectors for malaria, dengue, West Nile virus, yellow fever, encephalitis and other infectious diseases.