Unknown larvae

Unknown larvae

Observation - Unknown larvae. Description: We found this strange thing on a Birch (we think) leaf, when we pulled it off, the little caterpillar fell out! If anyone could tell us what it is, that would be great, thanks!

We found this strange thing on a Birch (we think) leaf, when we pulled it off, the little caterpillar fell out! If anyone could tell us what it is, that would be great, thanks!