You can add water and float them out and use a spoon to collect them. That or you can add expanding peat plugs, they come in disks and expand in humdity. Those you let the springtails crawl up on and you can either put them in the tank or shake them off the plug. I have used either method. In Ecuador the lab would use and turkey baster and blow the springtails off the peat and into another cup. This works best only when you have a great deal of them to harvest. I had switched to using leca or gravel and a bit of water-- to collect I flooded them and poured the water into another cup. This I dumped into the tanks.
j