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Observations on Medetera jacula (Fallén, 1823)
Nikita Vikhrev

M. jacula, a painfully common late summer-autumn species?

Jere Kahanpaa (
Being very common, large and comparatively easy to identify Medetera jacula presents a good opportunity to observe Medetera behaviour.
During the period 2 August -15 September, 2006 I observed the life of Medetera jacula (= Medetera in text) on an old Salix alba growing on pasture near a small pond, Moscow region, near Dmitrov town, for a total of 30 hours.
Medetera was numerous on chosen trees during all periods of observation; often I could see 3-8 flies at once. In mid September Medetera suddenly disappeared; on 9 Sept they were still common; on 14 Sept I found only 3 specimens; on 15 Sept not one.
On the trunk they concentrate mostly between 0 and 1 m high, but some flies may be seen up to a height of 3 m. It seems that for Medetera it does not matter whether it is a sunny or shadowy part of trunk, but when the weather is rainy, they prefer (not exclusively) sites of dry bark. During rain I found more flies at a height of 1-2 m. Cold and rainy weather does not disturb Medetera activity. Also Medetera could be found on the grass around the tree. I have seen both sexes in approximately equal proportion. Medetera are active till deep twilight; once I even observed a hunting fly 15 minutes after astronomical sunset in cloudy evening.

Most of the time Medetera sits motionless on the trunk, looking towards sky with abdomen down and head up. This position seems to be on one hand most ergonomic, on the other hand it gives highest possible field of view. Let it be called 'waiting' position.
When detecting the prey Medetera changes position into 'hunting' one, with the body parallel to the trunk. Thus Medetera is ready to attack or run after the prey along the trunk. If the prey stops moving, Medetera freezes in hunting position too and leaves freezing for 5-20 sec.
When eating the prey, the fly again uses waiting position. I very often observed the cleaning procedure immediately after feeding. Females in most cases regard head cleaning to be enough (fig. 1), males on the other hand seem to be more tidy, but they do not regard head cleaning of such importance, being much more concerned of hygiene of their genitalia.
For overnight they seem to use a special position with the body parallel and pressed to the bark.

< - - - Please note: There are another three pages in this article! - - - >
#1 | Susan R Walter on 22 January 2007 14:18:06
Really interesting (and amusing) article Nikita. The feeding strategy details were particularly fascinating.
#2 | jorgemotalmeida on 24 January 2007 20:48:36
NIkita, mystery solved! smiley your avatar is a doli fly.
FANTASTIC article. I wish to see more articles like this one. Smile one day I hope to contribute with 1 article! Wink OR more. Smile
#3 | diphascon on 24 January 2007 22:19:22
Very, very well done!
#4 | crex on 25 January 2007 16:27:16
Interesting. Well done, although it should have been made as a PDF Wink
#5 | Stephen on 07 February 2007 22:10:19
Fantastic! Observations worth of Fabre.
#6 | Cheryl Moorehead on 14 February 2007 07:46:51
I really liked this article. I've only been aware of these flies since I started macro work. They hunt barklice on my Hemlock.
#7 | Toby on 31 March 2007 23:52:16
fascinating, I had no idea flies eat springtails.
#8 | LordV on 01 April 2007 08:24:11
Wonderful article
Brian V.
#9 | conopid on 02 April 2007 18:38:09
I have only just read this. It is a very impressive example of observation. If only more of us would do this type of thing, we could learn so much more. Well done.Smile
#10 | Juergen Peters on 04 October 2007 16:35:24
Very interesting! I have seen Medetera (most likely (near) this species according to I. Grichanov) here also numerously on tree trunks in the last days, even at night in garden. One behaviour I found remarkeable: when sitting head up at the tree, they tend to lean from left to right and back when disturbed slightly. Looks like they were dancing... Cool
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19 February 2019 05:44


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14.02.19 11:14
hello everyone, I come back. Snowy today in Inner Mongolia, China

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I looooove the fly in the beer irish joke in the random quotes Grin

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no blanks in filename, file size reduced (below 300 k or so).Did you fulfill these criteria ?

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Thanks for the explanation Paul. It definitely stopped me from flooding the forum with my threads Wink

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Each user has a maximum of ten new threads per day (24 hours). Just to prevent a single user from sending scores of his unidentified fly photos at once and thus drain out any other threads.

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