Small space-dwelling creatures encountered by Voyager in 2372 that swarmed over the ship as a potential mate, while their energy field pushed Kes into her elogium years early.
In the episode Elogium, Voyager comes upon a swarm of small, tadpole-like organisms that live and move in open space. Curious, the crew approach, and the creatures cluster around the ship and attach themselves to the hull, their combined field draining and disrupting its systems.
The same field throws Kes into the elogium, the single fertile period of an Ocampa's life, long before it is due, and she and Neelix must decide at once whether to have a child. Chakotay meanwhile works out that the swarm's behaviour is courtship.
A much larger creature of the same kind arrives and rams Voyager as a rival. Taking a cue from a smaller creature that submits to it, the crew roll the ship over and vent plasma so that the hull turns blue. The large creature loses interest, the swarm follows it away and Kes's symptoms fade.