Two members of the Swarm species.
The Swarm species was an unidentified territorial and hostile race which controlled a vast region of space in the Delta Quadrant as of 2373.
Although she knew that taking Voyager through Swarm territory would be dangerous, Captain Janeway decided to do so, since going around it would have taken several extra months.
Their language could not be translated by a standard Federation universal translator. Their ships were shuttle-sized, but, when working in large groups, could disable a bigger ship by swarming it, landing on its hull, draining power from it, and finally transporting a boarding party aboard. (VOY: "The Swarm")
In 2376, members of this species appeared in the audience of a Tsunkatse match. (VOY: "Tsunkatse")