3rd of October:
I noticed some small eggs on my Silene cf. vulgaris seedlings, so I took a picture to see them up close.

6th of October:
It appears the eggs have hatched into the leaves. So they were leaf miners.

16th of October:
I have found one of the miners trying to change leaves. I have no idea what species they might be, but this website gives some potential suspects:
https://bladmineerders.nl/host-plants/plantae/spermatopsida/angiosperma/eudicots/superasterids/caryophyllales/caryophyllaceae/caryophylloideae/sileneae/silene/silene-vulgaris/

18th of October:
The population is not sustainable and the leaves are almost all eaten up. There are around 7 leaf miners in total, maybe a bit more. I have collected one of them for some close ups and to limit a bit their population. It later died as it got dehydrated. I gathered one more, but I had closed the cup with some paper towels, and the 2nd one died by touching them, losing all it's moisture.

19th of October:
All leaves are eaten, and the leaf miners hang out on the stems. Some seem to head for the soil.
This was the last time I saw them up to now. They must have burrowed into the soil.
Before that, I had gathered one more, which I managed to keep hydrated and feed with some Cerastium sp. leaves I found in the area. I will try to raise it to adulthood so it might be identified and the photos might become useful to some people.

25th of October:
The larva has eaten two and a half a leaves and disappeared inside the rubble of soil and debris (which I left to soak up the excessive moisture) inside its cup. I hope it hasn't died and just turned into a pupa without me noticing it.

4th of November:
Today I decided to check whether the experiment had failed, so like an archaeologist, I tried to dig up slowly and carefully the soil I had put in the cup.
To my relief... the larva had turned into a pupa! I will upload the photos tomorrow.
Now we wait...

13th of November
Today I woke up and noticed the fly had emerged from the pupa.
I took some pictures while it was inside the cup, but those unfortunately are not enough.
Even if morally I disagree, I have to refrigerate a bit the fly, so that I can take some close-up shots without killing it.
I managed to take a lot of close-up shots, though no focus stacks, and I am happy with the result, as the fly survived and flied away afterwards when I released it. I believe it is a Pegomya.