A drak swarm
Draks are a two-foot long insectoid creatures that travel through space in massive swarms -- large enough to hide a fully-grown Leviathan from scans by other spacefaring vessels and often confused for asteroid . Draks are extremely rare, native to the Delta Quadrant but seldom seen even there.
Draks are largely harmless, however they cannot reproduce in space. To reproduce, they need a warm space -- the warmer, the faster their rate of reproduction. To that end, draks will infiltrate spaceships and seal up a portion of the vessel with a quickly solidifying blue substance that they can produce from their mouths. This will create an area where the drak monarch can nest and complete the drak genesis.
Draks are able to duplicate DNA from the creatures they encounter, impersonating crew members of ships they have boarded. These duplicates are unable to speak, but are otherwise perfect copies. The DNA procured can be samples of blood or hair, often procured through use of barbed projectiles. The drak monarch can use a similar projectile to possess a sentient being and use them to communicate.
Sources[]
Draks are seen in an episode of the first season of Farscape.