In South Africa, there are predominantly two types of flies that cause worry and irritation to horses (and pets). Typical examples are the common housefly, which is a nuisance fly, and the blood-sucking stable fly, which causes intense irritation.

All flies have a standard life cycle which starts with the adult female laying eggs that hatch into larvae, which grow in size and have several ­stages, then pupate like the cocoon of silkworms, from which the adult flies emerge again.

In the case of the housefly, the complete lifecycle can be completed in as short a period as two weeks and stable flies in as short a period as seven days, when environmental conditions are ideal.

Control the cycle
If fly numbers are seen to explode in a short period, this is because the conditions are ideal for breeding. The only way to tackle fly control is to apply a fly management programme that tries to control the lifecycle.

If a fly management programme is undertaken, it should be recognised that it must be intensively maintained for a period of at least 3-4 weeks, in order to reduce the fly population throughout this period, as only then will there be an interruption of breeding numbers to have an impact on the fly population. Any fly management programme has to include several methods of control.

The lifecycle and the habits of various flies will dictate which methods of fly control can be applied to achieve success in a fly management programme. For example, houseflies are attracted to faecal material and rotting material where eggs are laid and where the initial small larvae feed and grow in size.

In the case of stable flies, their ideal breeding site is freshly cut lawn clippings. Houseflies are attracted to any wounds or excretions from e.g. the nose and eyes as well as the genitalia. Stable flies are driven by the need to suck blood, and are stimulated by body heat, body odour and the CO2 from animals breathing.

A fly control programme could include the measures as indicated in Table 1, where specific products may be recommended as the elements of the programme.
Typical fly control procedures include three main methods:

Mechanical methods
The use of a swatter will be applicable but achieves minimal impact on numbers, ­although it gives great satisfaction!

Methods which can trap or kill houseflies ­include flytraps with decaying protein material inside them, sugar solutions that are for ­example placed in a saucer or painted onto walls and stable areas (which contain an ­insecticide for the flies to consume). The ­mechanical sticky insect tapes and fly strings can be used to catch houseflies, and the fly strings in particular have proven most successful. Fans will distribute the attractive smells from animals that allow blood sucking insects to find their source of a blood meal. They generally only work when installed in stables.

Breaking the lifecycle
One of the simplest means of control of houseflies, is to create a breeding medium for them where they cannot complete their lifecycle. The ideal system that is utilised at horse stables is that a solid (e.g. cement) base is built with a small gutter around the total perimeter of the solid surface. The faecal material and bedding is then dumped on the solid surface. This is an ideal trap for houseflies to breed in.

In the lifecycle of the housefly, after the eggs have hatched, they develop into a type of worm (which are termed larvae) and these grow in the decaying material until such time as they reach a size when they need to pupate to move into the next stage, which is the adult fly.

These fully grown larvae need to move out of the decaying material into soil. This could be immediately below the decaying material (if not on the above cement slab), or alongside the decaying material, where they migrate a short distance and then pupate.

If there is a gutter around the solid cement base, the mature larvae that try to migrate to soil, will fall into the water-filled gutter and drown. In this way no chemicals are needed to kill or to block the lifecycle. Birds will also eat the larvae in the gutter.

The ideal breeding medium for stable flies is freshly cut grass after mowing of lawns etc. If the grass that has been mowed is placed in a similar solid surface composting area, this will attract the stable flies to breed in the composting grass and they too will experience an interruption of the lifecycle, as their mature larvae cannot reach the soil to pupate.

Chemicals
There are numerous chemicals which can be used to control flies:
• Insect growth regulators: Added to breeding sites that prevent the immature stages becoming adults.
• Insecticides: For application to animals, their housing or in baits/traps.
• Pheromones: These are insect attractant hormones that are usually used together with an insecticide.
• Physical barriers: Protective shields, curtains which may include insecticides or repellents.
• Environmental spray systems releasing insecticides or repellents into the animals environment.