White insects swarming on my potting mix

[Grayson]

I don't know what they are, but they only appeared this evening after 2 days of non-stop light-moderate rainfall. I checked the leaves and the stem and didn't find any. Also, they seemed to be congregating on only one pot. I saw a few stragglers on the bucket beside it - also on the soil.

They were moving slowly and didn't seem to be bothered when I poured water on them. When the water drained through the soil, they started milling about again.