|“||Observe this Hornoad, unimportant creatures that jump up and down.||„|
Hornoads first appeared in Metroid II: Return of Samus, where they lived in the tunnels of their home planet. They were very weak and could do little besides jump at Samus as an attack. They would often give missile ammunition when defeated. Machines called Autoads that were behaviorally very similar to Hornoads could also be found on SR388.
Hornoads later made a return during the events of Metroid Fusion. When Samus was escorting Biologic's research team on SR388, she was attacked by an X Parasite mimicking a Hornoad. Upon being hit with a Missile, the parasite reverted to its gelatinous form and infected Samus, eventually leading to the removal of parts of her Power Suit and her inoculation with the Vaccine "Metroid". The portions of Samus' suit infected by the Hornoad-X would later become the SA-X. When Samus was sent to investigate an explosion at the Biologic Space Laboratories research station, she found the station overrun by the X. Hornoads were among the infected and mimicked wildlife and could be found on the Main Deck and in Sector 1. These Hornoad-X had gained the ability to spit globs of acid at Samus, but they remained exceptionally feeble.
The Hornoads found in Fusion have a slightly altered appearance from the ones found in Metroid II; most notably, their color scheme has changed to blue-and-purple, their backs now contain warty protrusions instead of a spiked surface, and their legs are more frog-like in appearance. The X has changed the Hornoad in form and nature- whilst normal Hornoads either have no teeth or conceal them, their X variant modifies their form to have more teeth and very aggressive behaviour. Their purple coloring seems to be restricted to the X-infected/mimicked variants -- natural green Hornoads can still be seen hopping around in the background of certain rooms in Sector 1 before being infected. However, this could simply mean that there are multiple subspecies of Hornoads with slightly different physiology. Either way, the new design has since remained unchanged. In Fusion, uninfected Hornoads will continually spawn from grey-green hives in the background, although no such structures are ever found on SR388.
Hornoads appear in green and red varieties in Samus Returns. The red variety is found in Area 3 and is stronger than its green counterpart. In addition, the Hornoad-X variety makes a cameo appearance in the ending of the game, where it appears after being infected by an X-Parasite and roaring ferally, heavily implying that this was how the X outbreak restarted itself, and that this was possibly the same Hornoad-X that infected Samus in the beginning of Fusion.
- The Hornoad-X featured in the live action commercial for Fusion has a different design.
- The website data states that SR388 was Samus' first mission. This is not true, her Zero Mission on Zebes was. However, it is more likely the data is talking about her first mission pertaining to SR388.
- A Hornoad becoming being infected by the X can be seen in an ending cutscene of Samus Returns as an allusion to the upcoming events of Fusion.
- Additionally, Hornoads appear several times in the Chozo Memories from Samus Returns. The second memory shows a Chozo collecting an Aeion Orb dropped by a deceased Hornoad while another is being feasted on by a Gullugg. Another shows an X infecting a Hornoad and transforming into a Hornoad-X which is witnessed by the Chozo leading to the Metroid being developed. Another shows Larva Metroids under the direction of the Chozo preying on a group of Hornoad-X. A group of Hornoad can seen observing the arrival of the Galactic Federation Special Squadron ship in the opening as well. During a cutscene when Samus' Metroid Detector first beeps when it detects a nearby Metroid, a Hornoad is shown being attacked and preyed upon by a Larva Metroid which is implied to later mature into the first Alpha Metroid Samus encounters.
- Old Bird's statement about the Hornoad being an unimportant creature is ironic given that during Fusion Samus is almost killed after being infected by an X Parasite from a defeated Hornoad-X which she assumed was a normal Hornoad due to being unaware of the existence of the X at the time. In fact, SA-X is implied to possess Hornoad DNA in addition to Samus' as it transforms into what appears to be a Hornoad/Samus hybrid form during the climax of their battle on the B.S.L. station, which makes sense as SA-X was born as a result of the Hornoad-X infecting Samus' Power Suit components which where transferred to the station after they had been surgically removed resulting in the Station becoming infected after SA-X used a Power Bomb to escape the Quarantine Bay. This is even more ironic considering normal Hornoads are common enemies in Return of Samus and Samus Returns.
- In Samus Returns it is shown that Hornoads are apparently low on the food chain as a Metroid is shown preying on one and Chozo Memory 02 implies that Gullugg feed on them, though it is possibly they where just carrion feeding on deceased Hornoads as they are never shown actually preying on them during Samus' time on SR388 and they are shown coexisting with live healthy Hornoads. However this does not stop the X from selecting them as hosts, indicating they are strong enough for the X to target them.