House dust mites (Dermatophagoides pteronyssinus) aggregate.More information about this behavior here :
news.bbc.co.uk/earth/hi/earth_news/newsid_9290000/9290068...Scale : mite length = 0.3 mmTechnical settings : - focus stack of 57 images - microscope objective (Nikon achromatic 10x 160/0.25) on bellow