Photograph of a dead fly. How can you identify the insects you find?

What insect is this? How can you identify the insects you find?

The mystery fly

How experts identify unknown insects

I first became interested in insects when I was about 8 years old. At first my interest was in butterflies, sparked off by "The Observer's Book of Butterflies". This cost me 5 shillings in 1953 (25p in today's money). However, the weekly wage was only about £10.00, and my pocket money then only 6d a week (2½p today). With 12d to the shilling and 20 shillings to the pound, it was expensive and I had to save up for it over many weeks. The book was much treasured and I still have it - my very first insect book! Nowadays it is very worn, a sign of how much it has been used in the past.

A year or two later, I was becoming curious about other insects I was finding. The next book I found was "The Observer's Book of Insects" - my pocket money was a little more as I was older, but it still took a long time to save up for it (I still have this one as well!). My insect library was now two much treasured books. By the time I was 13 years old, I had become very interested in beetles - and that has stayed with me ever since. However, there was no "Observer's Book" on beetles! In fact there were no books suitable for a beginner at all!

Then, in 1959, when I was 14, Warne published the "Beetles of the British Isles" in the Wayside and Woodland series. These were bigger books, and at 12 shillings and 6d cost 2½ times more - and there were 2 volumes, a total price of £1 and 5 shillings! It took much longer to save up, but I was able to buy them in 1960. At the same time as my interest in insects developed, I kept my interest in books on insects. This meant that I have bought books on insects whenever I could afford them throughout my life. A situation encouraged by my specialising in entomology when I was at university. The result is - I have a "nose" for second hand insect books (and new ones). This means that over the years I have built up a very extensive library of books on insects.

In my role as registrar of the AES, I often receive questions about insects. These usually refer to a picture of an insect the member includes for identification (either a drawing, or a photograph). Often I know, or have a very good idea, what the insect is. Sometimes I have to send it on to a specialist in that group of insects. I try to avoid this unless I really can't - most specialists are very busy and often cannot spare the time. Recently I was sent an interesting observation on a particular type of caterpillar. I sent it to a specialist, who sent it on to another specialist as he wasn't certain about it himself. Another example was a photo of a dead fly sent by a member - it was a low resolution digital photo, and lacked detail - so how did I deal with this?

The best way of identifying is to use a key and this should always be used whenever possible. For many insect groups keys are not available and in any case there was not enough detail in the picture.

To me, it looked a bit like a robber-fly (Asilidae), but as a beetle person, how did I know of robber-flies? This is where looking things up in one of the field guides, such as Michael Chinery's "Insects of Britain and Western Europe", has helped. This has more information and illustrations than the "Observer's Book". Sitting reading such a book, (for pleasure!) and trying to gain an idea of what things are that you've seen in the field does give a broad knowledge of the range of insects.

Back to our fly - I started with the Wayside and Woodland book, "Flies of the British Isles" by Colyer and Hammond. On checking the index, I looked up the various references to Asilidae. I quickly knew it was not a robber-fly. What do I do now? I still felt that it did look a bit like a robber-fly, so I thought that I was in the right part of the book. Hence, I started looking at the flies on the plates adjacent to the robber-fly plates. I soon found a species on a black and white plate - a member of the Therevidae. Unfortunately the text gave me no idea as to the colour of the imago/adult (though it did tell me a lot about the larva). I checked in Chinery, but the colour was different.

A more advanced book was needed, so I took "British Soldierflies and their Allies" by Alan Stubbs and Martin Drake off the shelf! I turned to the main entry for Therevidae. The general features seemed to fit (at least, those I could see in the picture). I turned to the colour plates, looked at the pictures and read the text. Luckily, the person who had sent the photo had included details of size and where and when it was found. I read the "blurbs" about each species and realised that it was Thereva nobilitata. This is common and very variable, and the various details fitted - I had arrived at an identification! Thereva nobilitata - the common stiletto-fly. It had taken about 5 minutes from start to finish to identify it.

This exercise teaches us several important things:-

By Nick Holford