What made this black cluster on a leaf? 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.

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: <

![enter image description here](

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