Are Flies Friend or Foe

My original intention was to talk about a small insect flying around our house since the warmer weather started. On the look out for mosquitoes, it attracted my attention because of its similar size and shape. It has long hind legs, bent at 45 degrees and dangling down and a slow, erratic flight. When not resting, its time is spent searching the walls and darting at any mark that might be prey.

Ants were rejected but any other flies, mosquitoes and 'midges' were snatched with the long, hind legs. Small prey was devoured in flight but it had to settle for larger meals that were held with the forelegs. As a mosquito eater, it is a useful 'friend' which adds much interest to my shaving time - the one in the bathroom anyway .

They are relatively long-lived, have been active for several weeks and are very welcome to stay as long as they want. They belong to the family asilidae (robber flies), which contains about 500 species in South Africa.

These particular individuals are of the genus leptogaster (Picture-winged robber flies), which includes many similar-looking species. I can't be sure of the particular species but wonder if any other folk have noticed them in this area. They certainly keep our bathroom  mozzie-free'.


I have mentioned 'insects' previously, when talking about 'beetles', but there is no harm in repetition to gain a better perspective. The statistics are quite 'mind-boggling' and, remembering that all species on earth are divided into plant and animal 'kingdoms', I take the liberty of quoting from "Insects of South Africa" by Picker, Griffiths and Alan Weaving (Struik), which has the statistics in their introduction.

'Insects are by far, the most diverse group of organisms on earth, and must intrigue anyone with the slightest interest in the natural world. The total number of named insect species lies between 800 000 and 1 000 000, which is about 55 percent of all known species on earth and several times the total number of vascular plants (260 000) or vertebrates (50 000).

It may be surprising that the number of insect species cannot be given with greater precision. The reason for this is that the number of species is constantly changing as many thousands of new names are added to the list each year. In any event, the number of described species is a mere fraction of the real number. Although estimates vary widely, the total number probably exceeds 6 000 000 species.

 It is a sobering thought that - given the current rates of habitat destruction - millions of these species are likely to become extinct long before they are named.' They go on to say how insects are of enormous importance in the functioning of natural ecosystems and to the lives of humans. They are the most abundant macroscopic organisms in most terrestrial and fresh-water habitats. Surprisingly they are almost completely absent from the sea, where they are largely replaced by crustaceans.'

There is a wealth of recorded knowledge and I encourage everyone to read the introductory portions of most wild life books, where much of the interesting information is to be found. Most of us are aware of the diverse functions of insect species - pollination, decomposition, consumers of plant matter, predation on other insects, spread of 'disease' in control of other populations and as a food source for numerous other species including humans. To counteract the insects that threaten our crops and our health there are thousands more that are beneficial to human existence.


The superclass hexapoda (six-footed) contains 33 orders, 30 of which occur in South Africa. After the largest order -  coleoptera (beetles) - which I touched on previously - one of the largest orders is diptera (flies) with many ecologically and economically important species. They are identified, in most cases, by having only one pair of easily visible wings (the hind wings being reduced to small, club-shaped halteres which are used for balance).

There are a few wingless species. The order diptera is divided into around 52 different Families, most with many genera which are divided into almost 16 000 Species known from the afrotropical region. It is obvious that only a few of particular interest can be mentioned here. Again I would urge those interested to stud a good reference book.

The insects that look like giant, slow moving mosquitoes are harmless crane flies of the family tipulidae which contains 250 species from this region. Mosquitoes (family culicidae) occur in four Genera with several species within our area. ONLY the genus anopheles, which can be identified by the way it sits with its tail up at 45 degrees, is capable of transmitting the malaria parasite.

 I won't say more here as I intend deal with mosquitoes and malaria more fully in the next letter. Biting midges of which there are over 126 species in the family ceratopogonidae cause itchiness after a painless bite. They breed in water bodies and some can transmit filarial worms and various viruses to humans. They also transmit african horse sickness and 'blue tongue' and may be the cause of opthalmia from feeding round the eyes of birds and animals.

Gall midges of the family cecidomyiidae, of which we have 25 Species, are responsible for most of the 'Galls' seen on many plants. Interesting that Britain has 600 species of this midge. The robber flies, mentioned above, are mostly predators of other insects and are beneficial to humans. Horse flies of the family tabanidae have an irritating bite for humans and animals and may transmit certain diseases to animals.

They vary in size, the largest being the hippo fly (Tabanus biguttatus) which can cause some distress to large mammals. There are four species of tsetse fly in the family Glossinidae - also blood suckers, which will be familiar to visitors to the Okavango swamps and the Zambezi valley. They have been eradicated from all but the extreme northern regions of KZN and Mozambique.

They are known to transmit 'nagana' to cattle, as do certain species of 'horse fly'. There are many species of 'hover flies', many with an ominous looking proboscis, but most of them feed on nectar and are beneficial to humans. There are species of the family Bombyliidae which parasitize other insects and can give a painful bite to humans when standing still for too long !

Bluebottles, greenbottles and blowflies belonging to the Family Calliphoridae are well known around animal carcasses where they lay their eggs. The 'maggots' help clean up rotting flesh and they are therefore useful to humans. These are the 'maggots' that they used to clean human wounds in early days.

The flat feather flies or pigeon flies found on many birds are Pseudolynchia canariensis of the family Hippoboscidae. They are blood parasites that can cause anaemia and death if present in great numbers. There are other species that feed on mammals. The 'putsi' fly (called 'mango' fly in this area) is Cordylobia anthropophaga of the family Calliphoridae. It lays its eggs on damp soil or washing or sweaty bedding or clothing.

The larvae burrow into the skin of humans or animals and develop just under the skin causing boil-like swellings. It is best not to try and squeeze them out when small as this will result in further infection. Rather suffocate them with vaseline or leave them, covered, until mature, when they can be easily 'popped' out. Not pleasant creatures !

Always ensure you iron clothing that has been hung outside to dry during the wet season, as this will 'kill' the eggs. In the same family is the pirate fly (of the genus Bengalia) which hovers over groups of ants, stealing eggs and food. The bot flies, that cause nasal bots in certain species of antelope and in the gut of various ungulates do not feed in the adult form and are rarely observed.

Most of the life cycle is within the mammal host and high infestations can cause death. There are 17 species in the family Oestridae and 12 species in the family Gasterophilidae which are recorded through the north west and eastern parts of South Africa. Of agricultural importance are about 375 species of small fruit flies of the family Tephritidae , many of which are pests among fruit crops.

There are 61 species of vinegar fly of the family Drosophiliidae which are often mistaken for 'fruit flies' when they hover around rotting or damaged fruit and alcohol or fermented drink. They can damage soft skinned fruit.

The well known house fly (Musca domestica) of the family Muscidae feeds by 'spitting' on its food and can thus spread bacteria. In the same Family is Stomoxys calcitrans or Stable Fly - smaller and blacker than the House Fly.

It is an aggressive and persistent blood-sucker that can torment mammals and can severely damage dogs ears unless controlled. They breed in animal dung and damp bedding. The best treatment for dogs is to rub insecticidal cream on the ears although this is messy for the owners.

While sitting at the computer I have just caught several spoon-wing lacewings (Nemeura gracilis) of the family Nemopteridae - all species of which are only recorded in the extreme west or southern Cape areas of the country. I have seen them here before but never bothered to look them up.

It just supports the comments made by Alan Weaving. You never know what new discoveries you will make in the world of insects. Some agricultural companies in this area spend hundreds of thousands of rands on importing beneficial insects to assist biological control in their fruit production.

Surrounding farmers need to take great care during their spraying operations, where these are necessary, not to destroy beneficial insects. Wrongly timed applications have a detrimental effect on the environment that belongs to all of us. 

By Dave Rushworth

Kruger National Park - South African Safari