Basic Introduction

In this chapter I'll first say something about the prerequisites and obstructions to become a dipterist and then give some hints on photography with a binocular.

Taxonomy is currently in an odd situation. On the one hand there are many people truly interested in natural history and ecology, and already invest time and money to make photos of insects. On the other hand taxonomists appear to be more endangered of extinction than the species they investigate. I think the most important reason is expressed by the response I got many times, when I told "normal" people what I do in my spare time: "But you don't kill them?" With very few exceptions, like large brightly colored butterflies, it is not possible to learn something useful about insects and how to name them, if you don't have the specimen. Without a considerable amount of knowledge, it can easily take an hour to check all the characters asked for in the key, just to get a reliable family name. And when you find a similar specimen you definitely want to compare it with the first one.

If you are already on the way to learn more about insects, here are three arguments which can help.

1. The common attitude of society is cant:
People would save the life of a fly or moth and carry it outside back to freedom. Then they drive on a motorway and commit mass murder.

2. Ecologically it's nonsense:
A female insect typically lays a few hundred eggs. If an entomologist catches a few specimens of one species, this amounts to about 1% of the offspring of a single female. To guarantee a stable population 99% must be removed from the whole generation.

3. Scientifically it's counterproductive:
If we want to preserve nature, we should at least know the species composition and its change in time.

O.k., let's start. What you need first is a key to the families of Diptera. The best one I've seen is from Pjotr Oosterbroek, where you also find an excellent collection of literature guiding you down to species level. But there are many more keys, most of them covering smaller areas like a country. Now you need some specimens.

An easy way to catch a fly is to use a glass jar or a transparent small plastic bag. Place it slowly over the fly and then push it down quickly. Almost always the fly tries to escape upwards, to the direction where it can see the most light. Just close the glass jar or plastic bag and put it to the freezer (-22°C). After an hour, or better next day, unfreeze the specimen and start investigation. If you immediately expose the frozen object to the warm air, you can see how drops of dew are forming on it, which mostly disappear after a few minutes. To avoid that use an airtight glass jar and leave it closed until the dew on the jar has disappeared.

Many of the insect keys for beginners are sold as "field guide", pretending you just go outside, catch a specimen and find its name with a magnification lens. I wouldn't recommend even to try that, because for a beginner this is highly disappointing. You miss most of the important characters, which are only visible at higher magnification, and end up in a guessing game. Before you invest a lot of effort and time, I'd rather recommend to buy a stereo microscope, traditionally called "binocular" by biologists. It shouldn't be a too old one because optics behaves a bit like microelectronics, it's getting cheaper every year. It's definitely a good idea to check out a dealer on the internet where you can have a look at different brands and types and even invest a day's journey, if necessary. Don't forget to buy one with a third tube to attach your camera. It is only a bit more costly and much more convenient than to attach a camera to the tube of an eyepiece. The dealer will surely inform you, that you need a "cold light source". So it will probably be useful for you to know that I'm still using a cheap one with a 20W halogen bulb, operated at 70% brightness. Only in rare cases (alcoholic material) I use a focusable 10Euro LED torch, comparable to a 60W bulb.

Now we have a fresh, vivid and movable specimen under the binocular. The first task is to get it on an insect pin and to direct legs and wings, such, that we don't have to touch it anymore when it's dried. Large flies (e.g. Calliphoridae) are pinned diagonally through the thorax to keep the characters in the middle and at least the characters of one side intact. For smaller ones (e.g. Fanniidae) we use micro pins ("Minutien"), pierced again diagonally through the thorax, but now the micro pin is stuck into a short strip of polyporus (hardened PE foam) which is then fixed on a normal insect pin (size 2). Since micro pins are too small to hold them in your fingers, you need appropriate forceps (try some old ones from your bathroom) and you will usually work with them only under the binocular. Very small specimens (e.g. small acalyptrate flies) are better side pinned. The acute end of the pin is pierced between ptero- and mesopleuron, but only as deep that you can't see it on the other side. Now the blunt end is stuck into a strip of polyporus which is in turn fixed on a normal insect pin.

Once you're more experienced, you'll need more specimens and will use a sweeping net. Having swept the net a few times over a meadow or bush it contains tens to hundreds of specimens. You can still try to extract as many as possible with glass jars and put them to the freezer. But at this point it could be easier to get some ethyl acetate from a pharmacy, put some drops of it on a tissue handkerchief, place it in a large glass jar, build a framework of wire and place it over the handkerchief, such, that contact of the net with the fluid is avoided - and you have a simple "killing jar". To use it, first swing the net quickly a few times to and fro until all specimens are at its bottom, close it with your hand right above the bottom, push it swiftly to the jar and close it as far as possible. After 5-10 minutes all arthropods will be dead. Put them on a white sheet of paper or card with a fold in the middle and then transfer them to a small glass jar. Store it again in the freezer. You'll soon find out that there are many more recipes how to catch and store Diptera specimens.

At this early stage I wouldn't advise to work with alcohol material. The colors look different in alcohol and dusting patterns are much more difficult to see. And most keys even expect you to use completely dried material, because this was what the author used to prepare the key (in a museum).

Now some words on photography under the binocular. There are five points I'd like to mention: orientation, white balance, brightness of the background, focus stacking, and scaling for presentation.

Again there are many methods to orient a specimen. Holding the pin in your hand is possible, but very inconvenient, especially at a higher magnification. You can try to use a cork stopper or modelling clay. I found it very convenient to use the "entoball" from It's a metallic globe with an opening on one side containing polyporus, where you can insert the pin. The globe is placed on a socket and can be rotated freely in all directions.

As the sensor can't know whether your are illuminating a red object with white light or a white object with red light, you must always apply a manual white balance. Consumer electronics cameras do an excellent job on that, check your manual. If you're using a "microscope camera", actually a bare sensor equipped with a USB interface, you have to do it in your image editing program. (In gimp you'd use the "levels" tool.)

Obviously a dark object against a bright background is difficult to recognize, to the human eye and also to an electronic sensor. But note the example below looks more "intuitive" than it actually is. When you replace the white background by a darker one, the whole image appears darker to your eye and "intuitively" you want to remove it. Being a non perfectionist I found it sufficient to use three differently colored cards, a black, a grey and a white one.

white background:
grey background:

You definitely have heard about focus stacking, a computer technique to merge a series of exposures taken at different focus levels into an image with extended depth of field. The special problem arising with a binocular is, that even if there is a third tube to attach the camera, only the optical path for one eye is redirected to the sensor. Taking a series of exposures to be fed into a stacking program will thus result in an oblique stack, which has to be corrected by a preprocessing step. I use "align_image_stack" to correct the oblique stack and "enfuse" for focus stacking, both from the hugin suite, which is an open source implementation available for all platforms. Focus stacking with a binocular make photos more pleasant to look at, but after a while you'll find out that in many cases you can do without it. In the example below the only important character is the short facial keel between the antennae. Vibrissae, arista, and ocelli don't help very much with identifying a Pollenia labialis.

As I'm sure you will do a lot of experiments with focus stacking anyway, below I chose an example where you can see a typical problem of stacking. The bristles on the frons are clearly visible on the single exposure on the left, but the stacking has calculated them away, because it found the eye facets more interesting. This often happens when you have two sharp structures, one above the other, in the same stack.

single exposure: stack of 12 exposures:

More important is proper scaling and sharpening of the photos. The typical size of a raw exposure is 3000x2000 pixels. Using more pixels usually doesn't give better quality. For web presentation, and even more printed media, these images have to be scaled down considerably. For this site I chose 1200x800 as the best compromise. It's a good idea to play around with the sharpening filters of your image editing program, in gimp it's "Sharpen" and "Unsharp Mask". Don't give up too early and especially don't make the mistake: sharpen, zoom in, say "Ah it's pixelised!" and give up. The user of a website doesn't want to zoom around in an image, but wants to see the characters in an instant.

only scaled:
scaled and sharpened:

After a while you'll not only have learned, that there a many more methods to catch and store specimens, but also have seen many images of (mostly male) terminalia, in many cases the only way to be sure that you arrived at the right species name. Among the most advanced keys is, e.g., the one on Fennoscandian Drosophilidae (Fauna Entomologica Scandinavica). Equipped with a good binocular, you can often see enough of the epandrium, surstyli, ... to make a reliable identification, but for photos with higher resolution you need to use a compound microscope, and start with clearing and dissection (Working at Higher Resolution)