This apparent small blob of semi-translucent jelly is a hoverfly larva. I discovered this one on my roses, and it loves aphids and should help to keep their numbers down.
I don’t know what species it is, but it is quite amazing to think that after consuming hundreds of aphids in this stage it will grow into an adult similar to what can be seen below. It is called the Marmalade Hoverfly (Episyrphus balteatus).
May 2018, rear garden, Staffordshire, England. © Pete Hillman