SCP-XXXX is an anomalous species of centipede. Fully grown, its total length (from head to anus) is approximately 6.5 meters. It has a pair of soft, extendable keratin flaps which can enclose its body (save for a portion of its head). When these flaps are fully extended, SCP-XXXX's exposed segment roughly resembles the face of an old man (with movement of its pincers simulating motion of the 'mouth' and 'jaw').

SCP-XXXX is native to Great Britain and Ireland. Like most centipedes, it is carnivorous, and spends most of its time burrowing underground. When hunting, it partially emerges from the soil, exposing its head and the middle of its thorax. It then extends its keratin flaps and arranges its lower legs into a semi-circle resembling an upright archway. Via an as-of-yet unknown mechanism, this produces a spatial anomaly that leads directly into its stomach. Once prey enters, the anomaly closes; paralytic enzymes combined with powerful acids are used to subdue and digest them over a period of several days. After consuming a sufficient quantity of meat, SCP-XXXX instances will often burrow and hibernate for periods as long as several years.

SCP-XXXX uses two mechanisms to lure prey into its stomach. The first is the emission of a pheromone that induces mild euphoria, suppresses fear, and encourages curiosity in warm-blooded mammals. The second is a sound that also functions as its mating call: It produces a repeating series of recognizable English phrases that resemble a heroic speech (typically describing a quest or prophecy that must be fulfilled by entering 'the archway'). These calls last up to three minutes before repeating. Although each centipede's call is unique, no variation in a single centipede's call has been recorded over its lifetime.

SCP-XXXX was first discovered in 1950 following a Foundation investigation into several disappearances reported in the town of Belfast, Northern Ireland. Agents noted the presence of DNA from several missing parties in animal leavings discovered in a nearby wooded grotto; the ensuing excavation uncovered three hibernating SCP-XXXX instances along with the bones of over seventy children.