text: These sound like Springtails, an Order called Collembola.\nNot insects but within a group of terrestrial invertebrates called hexapods. A book with a key to the orders of terrestrial invertebrates would help in placing this groups lineage (phylogeny: how animals fit on the family tree). Springtails hang out in the soil feeding on decaying stuff. \nThey probably come out during the rain because the conditions are ideal to breed or they dehydrate less.....many terrestrial invertebrates dehydrate easily and need moisture to get out and about.\nCheers.