Flies and blowflies reside within the Diptera family. They complete four phases in their life cycle: the egg, larva, nymph and mature fly/blowfly. The first three stages are called immature stages.

Lees dit in Afrikaans

House, stable and face flies are the species mostly found on farms. Their numbers can increase considerably in summer, amid wet conditions and when compost and manure are available.

Every kilogram of manure or compost can contain up to 5 000 fly larvae. These fly species irritate animals and cause their feed intake to decline. They can potentially transfer diseases such as brucellosis, eye infections, salmonella and mastitis.

Blowflies are a troublesome pest that not only transfer disease, but can also cause large-scale tissue damage to animals. Mature blowflies are free-living, but the maggots (immature stage, also known as screwworm) feed on animal tissue.

Effective control

Dips or pour-ons containing a pyrethroid such as Decaspot 0,5% (G3433), Clout (G1447), Triatix Plus pour-on (G3434) and Decatix 3 (G1348) are effective against flies. Keep the environment clean, repair water leaks and spread compost and manure to let it dry. Bait containing fly poison can also be put out. The best-known blowflies are metallic coloured. These blowflies have a shiny metallic gleam that can be green, blue or purple. They include green blowflies, European green blowflies, copper-tailed blowflies, blue blowflies (bluebottles) and striped blowflies.

Eggs are laid in carcasses and hatch within eight to twelve hours under favourable conditions. Larvae can feed and shed their skins within three days, complete the nymph stage eight days later and emerge as a mature blowfly.

Under unfavourable conditions, e.g. during winter, the process can be delayed by a few months. Blowfly numbers increase especially after the first rains in spring, decrease in the hot summer months and increase again in autumn.

Veterinary importance

Several kinds of blowflies in different stages are attracted to rotting animal tissue. Green blowflies, copper-tailed blowflies and blue blowflies usually arrive at the carcass first, where they feed and lay their eggs. They play a major role in spreading anthrax over large distances. The larvae of these blowflies usually have smooth bodies.

Under certain conditions, primary blowflies adapt and breed on live animal tissue, rather than on carcass tissue. These conditions occur mainly when there is prolonged moisture present in the wool of sheep, causing decomposition of the wool and upper skin layers (lumpy wool).

Sheep with wool that is constantly wet, are especially susceptible. Conditions that may lead to this are diarrhoea, perspiration in skin folds, fleece rot, other wounds and long wool around the penis or vulva.

After decomposition and once the presence of primary blowflies has caused animal tissue to liquidise, secondary blowflies (striped blowflies) are attracted. These larvae are ‘hairy’ due to protrusions on their bodies. In cases where primary blowflies attack live animals, the larvae enlarge the wound by tunnelling into the live tissue.

Good hygiene

Ectoparasitic remedies can be sprayed on sheep during high risk periods (September to March in the summer rainfall areas or March to August in the winter rainfall areas), and can be used in conjunction with good farm hygiene practices against blowflies. Good hygiene includes timeous burning or burying of carcasses. As far as possible, try to prevent open wounds that will attract blowflies. Animals’ tails should not be too long or too short. Wool on the breech area can also be sheared, especially in ewes.

Dips can be applied specifically on high-risk areas of the body (such as the breech area or around wounds). An ideal remedy that prevents blowfly attacks is Expel Plus Jetting Fluid (G3941), containing Novaluron, an insect growth regulator that prevents the immature stages from maturing. It also contains Ivermectin, which kills red lice and blowfly maggots on contact. It has a long-working action. Expel Plus Jetting Fluid provides protection against blowfly attacks for up to 16 weeks.

In sheep that have already been attacked by larvae, the wool should be shorn around the wound, as many larvae as possible removed and the wound disinfected. Expel wound spray (G3245) is ideal for wound treatment. It contains deltamethrin, which prevents screwworms and disinfects the wound at the same time. Long-acting antibiotics can also help infected wounds to heal faster. – Dr Sumari Potgieter, technical and product manager of Afrivet

For more information and references, phone 012 817 9060 or 0860 VEEARTS, or visit www.afrivet.co.za.