What is this???

Me too Leuba.
Thanks Leuba
Thanks Mark
Thanks Marta
Thanks Lauren

How fascinating - I've learnt something new ! Thanks Martin et al.

It also looks to me like one of these shielded larvae that attack the ants nests when I look at it from below but I am no expert...:-)

Good job team. :)

Seems it pupates in its larval skin so the plot gets quite fascinating.
I'm still sticking with pupa.

This link shows larva and pupa

Here is a cute (translated) description;
''Here is the larva of an ant hoverfly (microdon sp.). It looks just like not really anything else, and was first described as a snail. It lives in ant hills, wherein the prowl around and vacuum cleaner. The ants can not really get taken on it so it can work quite undisturbed. To the right is in its natural environment. Slink sneak.
Fly Larvae are want to pupate in their larval skin, which then becomes stiff and firm. The formation is called a puparium. When the fly has finished blow it out of pupariet and crawls away. Below is an empty puparium of formic buzzing fly ''
- http://www.vestrehus.dk/dyresider/svirre...

Martin, this is so interesting. Looks so scale-like with two openings on the under side - ? pre-pupal stage. I assume you found it stuck to the wood - otherwise, I would have thought that it was a dried half of a seed kernel.

I've checked out syrphid larvae - most are maggot-like as you would imagine. This one has not even the slightest hint of segmentation externally, like most larvae do.

Very interesting upper side !
Will keep looking.

Not sure Mark. That was my first thought too.
And a search for the 'microdon + lava' confirms your suggestion!
http://www.diptera.info/photogallery.php...
Thanks!

Wow! That´s a weird one!

Looks water-tight from below - has to be a pupa then ?!!

Ken certainly sounded sure of himself. Wonderful thing.