The Parasite is a small green creature indigenous to Tallon IV, known to be a common pest throughout the galaxy. Parasites are highly versatile, able to adapt to nearly any given environment. They tend to travel in large swarms, big enough to take down creatures several times their own size. They come in many subspecies varieties, including the tough-skinned Plated Parasite, the Ice Parasite that lives in colder regions and the nightmarish Parasite Queen, born from the Space Pirate's Phazon Bio-weapons Research.
Samus Aran first came across Parasites en masse within the crippled Space Pirate Frigate Orpheon. Here they were seen wandering the airshafts and within containers in biological research labs. She later discovered that these creatures were being used as a test specimen by the Pirates, who were using a powerful mutagen called Phazon to create bio-weapons. The results of an experiment on a female Parasite were astounding. The creature had developed many new combat-focused traits, including an armored carapace, extra rows of razor-sharp teeth and so on. The creature had grown larger and stronger, with many improvements to its defenses and reproductive functions. It was dubbed the Parasite Queen by the Pirates.
Strangely, typical Parasites were only seen by Samus aboard the Frigate Orpheon, and not on Tallon IV proper itself. Why this is remains a mystery.
- Metroid Prime(First appearance)