"The Many" were an ancient non-sentient lifeform which functioned as a collective hive mentality. According to Spock's analysis, the three different types of animal found on Talin IV's moon were different only in species, but "the many" generally refers to the worker insects, not to the ships or algae-growers.
The many measure one and two meters long, with a two-segmented, wasp-like body, mottled black and silver. Each segment was supported by a set of four spindly legs, ending with wide flat pads.
The Many shared a symbiotic relationship with massively larger lifeform called "the One". Both species were believed to have existed in an earlier universe, prior to the Big Bang, given the unusual nature of their subatomic structures.
The Many operated solely on instinct, compelling it to grow food for the One, lacking much in the way of intelligence outside of their programmed parameters, to the extent that they referred to other life-forms as simply "strange life", and responded to questions about where they were with "Here". To achieve their goal of growing food for the One, the Many would seed target worlds with a certain strain of purple waterborne algae, and create planetary conditions for the algae to grow. To promote these conditions, the Many, through billions of years of evolution, developed an ability to manipulate advanced technology controlling nuclear weapons, by which they could provoke the release of large amounts of atmospheric radiation. In turn, the One would carry large colonies of the Many across interstellar space and closer to sources of the hard radiation they needed for survival.
The Many were discovered in 2269, following the Talin IV disaster, on the moon of that world. Upon discovering the nature of the Many and the One, it was determined that the Starfleet Corps of Engineers would convert the gas giant Talin VIII into a food source for the One, in order to protect Talin IV. (TOS novel: Prime Directive)