Sketchy-ish information but I think it could have been Twilight Zone/Outer Limits. Earth is being overrun by killer somethings? Moths/butterflies. Astronauts go forward back or forward in time to destroy them. Only for closing scene to show pupae on outside of spacecraft ie. They brought
Seems like the plot of Philip K. Dick's Meddler.
In it, people use the "Dip" to travel through time. The protagonist is sent to the future to understand an impending doom to humanity, caused possibly by prior uses of the Dip. He finds a race of vicious butterflies that are hostile and harmful to humans.
He closed the last switches. The indicator lights flickered, the floor chugged under him. He threw the main lever. More butterflies were pushing in, crowding each other eagerly, struggling to get through. A second circle of metal crashed to the floor suddenly, emitting a new horde. Hasten cringed, backing away, the blowtorch up, spouting flame. The butterflies came on, more and more of them.
When he travels back to his time, he finds the time capsule covered with cocoons, some of which have already opened.
Hasten's heart stopped beating. He pushed past them, staring up. At first he saw nothing on the metal hull, only the corroded metal surface. Then chill fright rushed through him.
Something small and brown and furry was there, on the surface. He reached out, touching it. A sack, a stiff little brown sack. It was dry, dry and empty. There was nothing in it; it was open at one end. He stared up. All across the hull of the Car were little brown sacks, some still full, but most of them already empty.
No idea if this was made into a TV show, but seems like a very similar plot.
With a hat tip to Andres F. for identifying the story, it sounds like you're referring to the short film; Meddler (2011), produced by Jonathan Rio and based on the short-story of the same name by Philip K. Dick.
"Time travelers involuntarily alter the course of time".
Note, this short isn't in black and white, but the lack of budget has led to a decidedly sombre colour palette being used.
The closing scene does indeed show pupae on the outside of their craft.