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I found this black slug-shaped thing on a leaf by my pond in western Sweden. It's about 15 mm long, positioned on a vertical leaf (I bent it to take the picture). enter image description here

And I don't even know where to start looking. I was thinking it might be an egg cluster, but can't find anything useful without knowing at least what kind of organism made it.

fileunderwater
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picapica
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  • @Canheguess I can't see any parts that I recognize as a larva (head, legs) and it's been completely still for at least 24 hours. Possibly a pupa I guess? – picapica Jun 14 '16 at 17:57
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    If you see them hatching can you take a photo of that too? I've wanted to see one of these for a long time but never found one. – arboviral Jun 15 '16 at 08:15
  • Nice picture and good question! – Remi.b Jun 15 '16 at 11:23

1 Answers1

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After a lot of scrolling through image searches I stumbled upon the answer: this is the egg mass of some sort of horse-fly (Tabanidae). Almost identical egg mass here: http://bugguide.net/node/view/21171

enter image description here

I'm assuming I won't get a more specific answer than this.

WYSIWYG
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picapica
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  • Thanks for giving an answer yourself. I was really curious. :) – AlexDeLarge Jun 14 '16 at 21:52
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    @AlexDeLarge Yes, me too! (Obviously enough to keep searching, compensating my lacking biology skills with patience.) – picapica Jun 14 '16 at 23:09
  • I am impressed! +1 – anongoodnurse Jun 15 '16 at 00:29
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    Try to hatch them! Another nice picture is found here, which includes recently laid and mature eggs: http://www.pbase.com/image/132217026 – fileunderwater Jun 15 '16 at 08:23
  • @fileunderwater Good idea! But I'm not sure I want to handle a bunch of horse-fly larvae, I would really prefer it if I could watch it happen out where I found it. It's just 50 m from my front door so I could go check it out quite often. Today is the third day that I've seen it in this black "mature" state, so it should happen within a couple of days (6 days seems to be a normal time until hatching) This page http://animaldiversity.org/accounts/Tabanus_similis/ says that they all hatch at once, so it's probably easy to miss! – picapica Jun 15 '16 at 09:58
  • @picapica You can put the leaf section in a jar (with very small holes for air). When little horseflies hatch out, you can choose their fate :P – WYSIWYG Jun 15 '16 at 12:53
  • picapica , if these are horsefly eggs (which I'm pretty sure looking at BugGuide), do you have many in your area? And do they bite you? I've been bitten by deerflies and they hurt! But never horseflies as they're slow and noisy. Easier to avoid – Jude Jun 16 '17 at 16:41
  • @Jude Yes, we have quite a few of them around. Mostly to slow to be a problem, but sometimes they manage to bite. The bite is a little bit painful, and then the swelling and itching is worse (but the reaction is very different from person to person). – picapica Jun 16 '17 at 18:06
  • Thank you! Any deer flies? I'd assume so if horseflies are around. – Jude Jun 16 '17 at 18:09
  • @Jude Those too! In Swedish (at least in my usual vocabulary) we don't have separate words for the different kinds of Tabanidae, so I can't really tell if some are worse than others. – picapica Jun 16 '17 at 18:19