I am trying to find a short story I read many years ago from an anthology. I remember hunters who time traveled to kill dinosaurs. They were successful in that they did go back in time with big guns and brought down something big, but they didn't anticipate what happened next: giant fleas and ticks leaping off their dead hosts, looking for another meal and finding only juicy warm-blooded mammals nearby. Does anybody remember this story? It was from around the 60s, I think.
It's Poor Little Warrior!, by Brian W Aldiss.
Claude Ford shoots the brontosaurus without the slightest difficulty, but forgets that when it died its parasites would leave it, and they would be far more dangerous. They pick his carcass loving clean.
So you pause, and as you pause, something lands socko on your back, pitching you face forward into tasty mud. You struggle and scream as lobster claws tear at your neck and throat. You try to pick up the rifle but cannot, so in agony you roll over, and next second the crab-thing is greedying it on your chest. You wrench at its shell, but it giggles and pecks your fingers off. You forgot when you killed the bronto that its parasites would leave it, and that to a little shrimp like you they would be a deal more dangerous than their host.
I read it first in Aldiss' collection Penguin Science Fiction, but don't doubt it's been anthologised many times since. It appeared in The Magazine of Fantasy and Science Fiction, 1958 and is available to read online (legally) here