The climate of an area provides an overall indicator of the potential level that fly populations may reach. However, facilities for confined-animal production greatly alter the environment.
In nature, predators have a significant role in regulating fly population levels. However, the concentration of animals and manure in confined-animal production facilities once again creates an unnatural situation.
The time required for fly development at different temperatures is discussed in the section: Fly Species & Biology.
The overall temperature range and prevailing summer temperatures in an area are crude indicators of how fast flies will develop and how many generations per year there will be.
The length of the fly season in the northern hemisphere generally increases from north to south, corresponding to the climatic zones. The higher the temperature and the longer the season of high temperatures, the more rapid is fly development and the greater the number of fly generations per year.
Because flies develop rapidly and generations overlap, large fly populations develop quickly and are sustained as long as temperatures are high.
However, confined animal housing alters the situation substantially, because it creates an artificially-protected environment. For this reason, even more flies and generations per year are likely to occur in and around confined-animal housing than the climatic zones would suggest.
The temperature maintained in the housing system will determine the fly population level more than the climate of the area.
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