Hrud

The Hrud in the Warhammer 40,000 universe are a race of spacefaring rodents roughly the equivelent to Space Skaven. Their technology is based on plasma such as their warp plasma gun on miniature game of Inquisitor. A unique concept behind the Hrud is that they exist in a dimension outside our own. Because of this it is theorized that they are able to phase in and out of their planes to further infest areas. They were supposedly all but cleansed by the Iron Warriors during the Great Crusade

Nonetheless, it's pretty hard to find out anything else about Hrud. They don't appear in any current books except for a very brief mention in the current 4th edition rule book. Though there is speculation that they may return as adversaries of the Alien Hunters (Warhammer 40,000) when their codex is released.