purpose what are flies for?

What are flies for??everything has a purpose but wats a flies and cockroaches??

Here's what I found:

Cockroaches are potential vectors of diseases such as dysentery, gastroenteritis, typhoid and poliomyelitis. Their diet is omnivorous and includes fermenting substances, soiled septic dressings, hair, leather, parchment, wallpaper, faeces and food for human consumption. The latter may be contaminated either by the mechanical transfer of causative agents of disease from the insect’s body, or by transmission in the faeces. An outbreak of food poisoning in a Brussels hospital subsided immediately an infestation of B. germanica was controlled.

http://www.the-piedpiper.co.uk/th2.htm

Flies:
second only to the bees and wasps, flies serve the useful function of pollination of flowers with nectar. [15] Though the thought may be infrequent, some flies are useful: (1) tachinid flies parasitize (prey on) the harmful gypsy moth, and (2) the fruit fly (Drosophilia melanogaster) is widely used in experiments concerning the functioning of genes and chromosomes. [16] Professor Thomas H. Morgan of Columbia University pioneered the subject of heredity in the field of genetics using the tiny fruit fly (Drosophilia). Ease of handling, low expense, as well as, requiring only ten days to complete a generation, made the fruit fly especially suitable for scientists to observe several lifetimes of heredity. [17]

http://fohn.net/pictures-of-flies/significance-importance.html

The purpose of any organism is to make sure it survives long enough to reproduce, ensuring the survival of its own genetic material. To that end, flies and cockroaches have as much purpose as the Ebola virus, flesh-eating bacteria, a tube worm attached to a geothermal vent five miles beneath the surface of the sea, or a bacterium buried in a chunk of icy rock orbiting Titan.

How an organism affects the other organisms around it is completely incidental, accidental, and coincidental. Everything is secondary to the overriding goal of reproduction.

to reproduce and carry on the survival of its species

to bug you and look icky... lol no those guys are right =)