Introductory page to the Diptera (Flies and Mosquitoes).

Introduction to Flies (Diptera)

All pictures of garden wildlife on this page are thumbnails. Click on a thumbnail for enlargement in format of 800x600 pixels. The enlarged photos are from 100 to 150KB in size. We normally use the animal's English name (if it has one). However the scientific name of the species is always mentioned in the photograph's captions. For some species an additional page containing more pictures is available.

Our original Flies Page got too big. Especially surfers using a modem had to wait a long time for the page to load. In March we decided to cut the original page into 5 new shorter pages. We also added an introductory page on the Diptera. If you are looking for a particular species or family of flies, please use the picture navigation at the top of the page, or our search engine at the bottom of this page, or make your choice below:

1 Mosquitoes, gnats, St. Mark's flies and crane flies, 2 Robberflies, Stiletto flies and Dance flies, 3 Hoverflies, 4 Fleshflies, Blowflies, Bottles, Houseflies and Root-maggot Flies, 5 All other fly families.

Introduction to Flies and Mosquitoes

Flies and mosquitoes are remarkable insects: they are very good flyers, yet have one pair of wings only. The other pair has almost disappeared, but can be seen as two little knobs on a stick at the sides. They are used for balancing during flights. There are some 120,000 species known, including the most common 'pet': the Common House Fly. Many more species still fly about undiscovered. Some experts believe that there may be well over 1 million species. All diptera belong to those insects that must go through all stages of development: egg-larva-pupa-adult.

Flies no longer have their hind wings. They are reduced to a little 'knob-on-a-stick", like in the Fever Fly to the left and the Crane Fly to the right.

Flies and gnats are not among man's best friends. Even biologists fear them: there are many species, often looking all the same and the majority of them is plainly looking and colourless. They are really the opposite of Butterflies and Dragon-Flies, which don't harm people and which are very colourful. Butterflies, moths and dragon-flies are very popular both among animal lovers and professionals alike. Even though flies are not that popular there are a few exceptions though. Quite a number of people is interested in Hover Flies, because of their attractive colouring and presence in gardens and on flowers. Other popular families of flies are the beeflies and the robberflies. Nowadays the parasitic flies are also extremely popular, for some species are useful in agriculture. But many of the other flies are ignored by most. A few groups however are studied intensively all over the world by medical people. Some of the gnats are not just irritating animals, they are distributing very serious diseases, such as malaria and dengue as well. Even the police is interested in flies, especially fleshflies and blowflies. When a decomposing body is found somewhere the police wants to know how long the body has been there already, or whether it has been moved. Fleshflies are very helpful, for they lay there eggs in bodies. So by examining how far developed the larvae or pupae are, one can conclude how long a body has been there. But there is more. Not all fleshflies deposit their eggs in fresh bodies. Some prefer older material, so by examining what species there are present within the body the picture becomes more complete. And so is the presence of the larvae of the Common Flesh Fly, for it doesn't actually eat the felsh, but it hunts for the larvae of other flies that do. But the Common Flesh Fly will not deposit its eggs when there are no other larvae present yet, so the presence (or absence) of its larvae also tells a story.

The Greenbottle to the left and the Bluebottle to the right belong to the best known fly species.

Robberflies and Fleshflies are rather big and easy to study, but the majority of flies is very small. Take the Fungusflies for instance. The bigger species will be some 0.5 centimetres (0,2"), but most are much smaller. Smaller still are most Mining Flies. The larvae live inside a leaf and eat it from the inside. A leaf however is not very thick, so you have to be very small to live inside of it. The mines can be detected easily by looking at a leaf. You have to be careful though, for there are not only larvae of flies living in a leaf, also the larvae of some wasps species mine leaves. Galls can be found on both the leaves and stems of various plants. They too can be caused by both flies and wasps. The adults of flies and gnats all live off nectar and other fluids. Many species even don't eat at all once adult. The adults do hardly ever have useable jaws, so most can't chew on food at all. Like in many other insects the larvae can live much longer than the adults. Some larvae may live for a year, while most adults die within one month, not counting hibernation periods of course.

Whatever the larvae may eat, adult flies need liquid food such as nectar. To the left a parasitic fly, to the right a hover fly.

It is not very difficult to tell flies apart from other insects: each insect having just two wings and no shields or something is a fly. This means a lot of insects are called flies, which actually are not flies at all. Well known examples of this are the butterflies and the dragon-flies. Scorpion flies, lacewings and may flies are more tricky as they often appear to have just one set of wings, but studying them carefully will reveal the presence of two pairs of wings.

You might think these are flies as well, but they actually have two pairs of wings, so are not flies at all. To the left a Lacewing and to the right a Scorpion Fly.

Identifying fly species is a different story all together. Sometimes you even need a microscope to tell families apart! Like for instance the Houseflies and the Root-maggot flies. Even though these are two separate families, the species of both look like another so much that only real experts can place them in the right family. Within the family of hoverflies there also a lot of look-a-likes are in existence. The drone flies present most people with lots of problems. These common flies, even in ordinary gardens you'll see a lot of them, all look alike, yet there are some 15 species in Western Europe alone. The name dronefly therefor often only refers to the Eristalis species as a group and not to just one species. Field biologists often have huge tables with them to identify these flies.

These are two Drone Flies: the the left Eristalis pertinax and to the right Eristalis tenax. But as you can see it is very hard to tell them apart!

Unlike in most birds and mammals in fly species males and females are almost identical, with a few exceptions only such as the Fever Flies. Yet it is very easy to determine whether you are looking at a male or a female. Males have very big eyes, that almost touch eachother at the top of the head. The eyes of the females are much smaller and always rather wide apart. This rule doesn't apply to most Gnats. With them you have to look at the antennae: females have smaller antennae, often not more than small wires, while males have huge antennae, often looking like a brush.

To the left a male fly with his big eyes, to the right a female with smaller eyes, farther apart.

Usually flies are not very good pollinators. Sometimes a seed manages to cling on to a hoverfly, but flies lack the hairs found in bees and bumblebees used to collect pollen. Yet there are plants depending on flies. One of the best known perhaps is the Stinkhorn (Phallus impudicus). It does not use flies for pollination, but just for spreading the seeds (called spores in fungi). The head of the mushrooms quickly desintegrates into a smelly liquid. The liquid smells like rotting meat, a treat for many flies. So they occupy the mushroom in great numbers. But the slimy liquid in which the spores float around attaches itself to all parts of the fly. After drying the spores are released, often far away from the original plant.

The Stinkhorn (Phallus impudicus) is a fly's main attraction in the woods.

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