What worm has natural selection selected AGAINST (which worm will not survive)?

Natural selection tends to select against parasites that have overly specialized life cycles, such as the fluke worm, which relies on specific host species for reproduction. If environmental changes or host availability fluctuate, these worms may struggle to survive, as they cannot adapt quickly to new hosts or conditions. Additionally, worms that are less efficient in reproduction or have weakened defenses against host immune systems may also be selected against, leading to decreased survival rates.