Flies
Flies, though generally harmless, can be a nuisance to horses causing stomping and rubbing. This in turn may lead to leg and eye injuries. The use of appropriate repellent along with physical barriers, such as mesh rugs and fly veils should be considered.
Mosquitoes
Mosquitoes and midges are an extremely important external parasite to control in horses due to their role as vectors for viruses, namely Arboviruses (eg. Ross River Virus) and Flaviviruses (eg. Japanese Encephalitis Virus). They also have the Potential to cause severe irritation and allergic reactions. Measures should be taken to prevent exposure to these insects, as above, with regular application of repellents and rugging. Owners can also stable horses during the most active periods of dusk and dawn. The use of stable fans may also be of use during times when insect levels are high.
Ticks
Various species of ticks will attach to horses. Most will cause local reactions, presenting as oedematous swelling around the attachment area. Along the east coast of Australia, Paralysis ticks must be taken into special consideration. Paralysis ticks can affect horses of any age and size, however miniature and young animals are considered most at risk. Prevention of tick attachment can be done by keeping horses in paddocks with short pasture and away from bushland, as well as the application of pyrethrin based products. Owners should also be encouraged to physically check horses.
References: business.qld.gov.au; Ruppin, et al. 2012.