A butterfly is a winged insect.
Collector kept a blue butterfly in one of his cells for some unknown reason. It was kept in a room along with Groot, Adam Warlock's cocoon, a praying mantis, and jellyfish. It's cell was in sight of Warlock and Groot.
The butterfly was not named.
It is unknown why Collector is keeping a butterfly in his cells. In modern times for the comics, Collector is obsessed with collecting anything he considers rare or valuable though he previously collected anything he saw as interesting. Either the insect is rare where it is from, meaning not Earth where butterflies are very common, or Collector simply likes it.