What is a Gadfly? What does it look like? Why was it such a bad plague for the Egyptians?

"Gadfly, a type of fly typically belonging to either the family Tabanidae (Horse-fly) or Oestridae (Botfly)"
http://en.wikipedia.org/wiki/Gadfly
"Females usually also feed on blood which aids in egg development."
http://en.wikipedia.org/wiki/Horse-fly
"dinoflagellate that secretes neurotoxins which make water toxic and which cause blood to leak from dying fish"
http://www.channel4.com/learning/main/netnotes/sectionid100663695.htm

The multitude of rotting corpses of fish and frogs attracts a very large swarm of flies, in order for that swarm to flourish they need lots of food for their larvae. Seeing as the Horse-fly is as viable a suspect as any fly for the fourth plague, we need to consider the fact that they feed on blood. A swarm that large is going to need a vast amount of blood!

Another suspect is "the stable fly, which lays around 500 eggs at a time...glanders which is spread by stable flies"
http://www.channel4.com/learning/main/netnotes/sectionid100663695.htm

((Edit: Sorry... here's the piccie))

The name Beelzebub is commonly translated as Lord of the Flies, although the meaning may originally have been quite different.
In the Bible, one of the plagues of Egypt may have been a plague of flies.


Ceratitis capitata, the "Mediterranean fruit fly" or "medfly", is an important pest of fruit crops.Diptera are a diverse order with an enormous range of ecological roles. Every type of trophic level pattern can be seen in the Diptera. Dipteran predators include the robber flies (Asilidae) [2]. A variety of herbivores can be found in the Diptera, such as the economically important fruit flies (Tephritidae). Flies are often parasites, including internal parasites endo- such as the bot fly and external parasites ectoparasite such as the mosquito, black fly, sand fly or louse fly. Myiasis is the special term for flies infecting living tissue (such as the screw worm fly). Many flies eat dead organic matter detritovores, plant or animal remains. This is especially common in the larval stage, seen in the filter-feeding mosquitos and black flies to the dung-feeding blow flies (Calliphoridae) or the organic deposit feeding rat-tailed maggot. A number of taxa feed on blood, including horse flies and mosquitos. Flies are also important pollinators for many species of plant, and many species feed on pollen and nectar.

The basic fly life cycle is egg, larvae (maggots — see below), pupa and adult (winged stage), called holometabolism. There is often a difference in food sources for larvae versus adult dipterans of the same species. For example, mosquito larvae live in standing water and feed on detritus while the adults feed on nectar as their energy source while females utilize blood as their energy source for egg production.

Flies rely heavily on sight for survival. The compound eyes of flies are composed of thousands of individual lenses and are very sensitive to movement. Some flies have very accurate 3D vision. A few, like Ormia ochracea, have very advanced hearing organs.

(wikipedia)