Biology and distribution Egle in Belgium

Who can help me with collecting willow catkin flies in Belgium?
Egle Robineau-Desvoidy en Belgique (Diptera: Anthomyiidae)

In spring blossoming willows attract a lot of insects, such as bees, butterflies and hoverflies. But when you take a closer look, you will see also small black flies that measure only a few mm. The scientific genus name of these flies is Egle and in English they are called willow catkin flies. The English name is very striking, because the imagines feed on nectar and pollen of willow catkins and the larvae develop inside the seeds. With some experience it is possible to recognize the imagines in the field because they have a clearly protruding mouth edge and a slender proboscis and slender palpi. But identification to species level requires dissection of the genitalia. However, collection is very simple because in fact the vast majority of small black flies on willow belong to the genus Egle. There is one exception, namely Egle concomitans which has no protruding mouth edge and has not willow but poplar as host plant.

Until recently only three species of willow catkin flies were known from Belgium. In recent years five species were added. Through this large-scale collection campaign I would like to get a better picture of the distribution of the different species in Belgium and their habits. Moreover, additional new species can be found.

Instructions for the collection of willow catkin flies

Read these instructions along with the excelfile ‘Form

• collect one or more specimens that are engaged in the same activity (e.g. all foraging on a male willow) and this at a particular location and only using a single trapping method. This is one sample.

• insert the flies of this sample in a tube or jar, optionally already filled with about 70% alcohol

• assign a sample number. The second sample that I collect on 3/04/2016 is named 20160403/002

• fill in one line in the Excel file ‘FormInEnglish’ for the considered sample

• EITHER put the specimens of the sample in a tube or jar with ca. 70% alcohol and add a label with the sample number written in pencil. Do not use a pen or a marker, because the ink dissolves in alcohol.

• EITHER you pin the specimens with a small needle and you pin also a label with the sample number under each specimen

• ATTENTION 1: do not keep the specimens in a dry box, because the hairs will break off and that makes the identification more difficult

• ATTENTION2: do not keep the specimens in a wet box, because the specimens will grow mouldy (thus add sufficient alcohol so that all specimens are flooded.

 • ATTENTION3: do never  add two samples in one tube, because this makes it impossible for me to know what specimens belong to what samples

Thanks to all enthusiastic contributors!

If you have any questions, don’t hesitate to contact me: