During the last glacial maximum, 25 Myr ago, ice sheet covered the North Atlantic Islands, Scandinavia into N-Europe and Britain north of London. During this time ice sheet extended as far as 100 nautical miles off the present coast of Iceland. Most likely no aquatic invertebrates survived, with the exception of newly discovered 2 species subterranean amphipods in the groundwater system of Iceland. It is evident from mitochondrial DNA that one of the species has been on the island for at least 5 million years. Other invertebrates have presumably colonized the islands after the Ice-Age, 10 Kyr ago. Their origin is Scandinavia and Britain and it has been possible to follow the colonization route of one Trichoptera species from Central-South Europe migrating along the W-Europe through Britain and Faroe Islands to Iceland, where as another parthenogenic Trichoptera originated near the Bearing Straight and one population migrated westward through N-Asia to Scandinavia to Iceland, where another population migrated eastward through N-America, Greenland to Iceland, where the populations meet without reproducing. The number of species on the North Atlantic Islands is a result of the distance these islands are from the larger regions of Western Europe rather than the sizes of the islands. For aquatic insects, about 5% of the Norwegian or British fauna is found on the Iceland, the island furthest away from these regions, whereas about 30% of the Cladocera (Crustacea) are found, but they have a resting eggs which can be transported by waterfowl. Also, the North Atlantic islands have only a few of the species in common, indicating the stochastic nature of the colonization.