As mentioned in the comments this sounds very like the story Swarm by Bruce Sterling. Only the beginning is different because in Swarm the story is set against the background of a conflict between different human factions in the Solar System.
An asteroid has entered the Solar System occupied by creatures collectively known as the Swarm. It is described much like an ants nest and the creatures show no sign of intelligence. The protagonist Afriel is sent to the asteroid with some plan of exploiting their resources to benefit his own side in the conflict. Afriel encounters a central intelligence who tells him:
"I find myself awakened again,” Swarm said dreamily. “I am pleased to see that there is no major emergency to concern me. Instead it is a threat that has become almost routine.” It hesitated delicately. Mirny’s body moved slightly in midair; her breathing was inhumanly regular. The eyes opened and closed. “Another young race."
“When you began your pheromonal experiments, the chemical imbalance became apparent to the Queen. It triggered certain genetic patterns within her body, and I was reborn. Chemical sabotage is a problem that can best be dealt with by intelligence. I am a brain replete, you see, specially designed to be far more intelligent than any young race. Within three days I was fully self-conscious. Within five days I had deciphered these markings on my body. They are the genetically encoded history of my race…within five days and two hours I recognized the problem at hand and knew what to do. I am now doing it. I am six days old.”
And later Swarm tells him:
"You are a young race and lay great stock by your own cleverness," Swarm said. "As usual, you fail to see that intelligence is not a survival trait."
Swarm is not a collector in the sense that its mission is to collect organisms, but it tells Afriel that is has collected fifteen other races that it encountered for defensive study, and it asks Afriel to join the collection:
“I invite you to become a symbiote. I have here a male and a female, whose genes are altered and therefore without defects. You make a perfect breeding pair. It will save me a great deal of trouble with cloning.”