If the soil is from America, or warm western Europe = Possible Entomobryomorpha soil springtail.............. these are 1.5mm long....... and are harmless detritus munchers, in fact a benefit !!......... bit like the RHS Microbial Microryzal zooplankton i use on my roots at re pot time......... got that one from Monty don !!...........
Entomobryomorpha soil springtail's are present, proving this manufacturer, did not treat, ultraviolet sterilize, the soil before packing, so could have black gnatt eggs in also, hatching at 26c..................... ALR