In 2367, the crew of the USS Enterprise-D first discovered one such solitary creature orbiting Alpha Omicron VII of the previously uncharted Alpha Omicron star system. The creature's mother was inadvertently killed when minimal-powered phasers were used in self-defense against the creature's aggressiveness.
The reason for the aggressiveness was discovered when scans by Lieutenant Commander Data soon revealed that another distinct energy signature was present within the dead creature. It was about to give birth, and had understandably attacked the encroaching Enterprise as any mother would. Dr. Beverly Crusher was able to use the ship's phasers once again to perform a Caesarean section, removing the newborn from its parent using a thin beam at 3% power. Once free, the newborn immediately imprinted on the Enterprise as its mother, and attached itself to the secondary hull, where it began feeding on power from the fusion reactors.
Soon dubbed Junior, it began a steady drain of the ship's energy, and increased in size 8.5%. It could not be allowed to continue without endangering the ship's life support systems. The crew extrapolated the parent's original course, leading them to a nearby asteroid belt. There, three additional full-grown creatures came out to meet the ship in response to radio emissions from the newborn. The asteroids contained meklinite, a substance which interferes with ships' sensor scans and may explain why the creatures were not previously detected. The asteroids also contained quantities of kefnium, which also comprised an element of the creatures' outer shells and may have been a significant part of their diet.
The crew of the Enterprise was able to remove the newborn from the hull (and "wean" it from its "nursing") by altering their engines' energy signatures to a different wavelength from the space-normal background radiation band of 21 centimeters (in other words, "souring" Junior's milk). As it left its surrogate mother, the other entities welcomed the newborn into their midst, and they all proceeded back into the asteroid field together. (TNG: "Galaxy's Child")
Geordi La Forge later recalled the incident with Junior in a conversation with Montgomery Scott during his visit aboard the Enterprise-D in 2369, describing him as being about the size of a four-story building. (TNG: "Relics")