Item #: SCP-7539

Object Class: Euclid

Special Containment Procedures: Instances of SCP-7539 will be captured with lure buses operated by MTF Kappa-3 ("Bus Barn"). Instances of SCP-7539 in containment will be fed buses once a week; to facilitate this, the Foundation operates a small shell company that claims to operate intraurban bus routes. Buses fed to SCP-7539 should not be fueled.
Description: SCP-7539 is a species of sentient metal-based life forms that exclusively prey on buses. They are four wheeled vehicles of various size and coloration.
SCP-7539's primary cognition source is a small titanium box. This box contains a standard car battery and a large amount of doped silicon; the silicon is arranged into logic gates that functions as a rudimentary stimulus-response system. Small silicon wires lead from this box to essential mechanical components (the engine, axles, digestive mechanism, etc) and serve as a signaling and coordination system.
No recognizable sensory apparatuses have been found on SCP-7539. The current hypothesis subscribed to by Foundation researchers is that SCP-7539 instances receive vibrational input from their tires, though this has not been conclusively established.
In order to consume buses, the front half of SCP-7539 instances splits apart across a vertical seam. This process uses a specialized piston and swings open on concealed hinges. While open, SCP-7539 instances will accelerate and scoop the target bus into the main body. Once ingested, a series of hydraulic pistons and rams pulverize the bus. Acids, heat, and mechanical agitation assist in the digestive process. Any pieces that cannot be digested, including upholstery and tires, are expelled from behind while the instance is in motion. The full digestive process has not been fully characterized; the metal is presumably used for growth and reproduction. These processes have not yet been observed in containment or in the wild.
Batteries within ingested automobiles are isolated and removed by an as-yet unknown subprocess, with the stored energy being transferred to the instance's brain. Gasoline is removed and consumed in another uncharacterized process.
Any humans inside SCP-7539 will be expelled before the alkaline breakdown via a specialized subprocess.1 The exact mechanism of this subprocess is not yet known; however, it is capable of detecting humans of all genders, races, and age, and cannot differentiate between humans and mannequins of approximate shape. Objects or collections of objects the same mass as humans will continue to the alkaline reaction stage, and will be expelled as normal. SCP-7539 instances will slow prior to ejecting humans; damage to humans ejected is usually low, consisting of abrasions, friction burns, or cuts.
SCP-7539 instances appear to exclusively attack and consume buses. The type, size, color, or purpose of bus does not appear to matter, with instances having been observed consuming school buses, tour buses, double-decker buses, and limousine buses. Instances will not attack vans, streetcars, trolleys, trucks, or limousines.
SCP-7539 instances specialize in a certain type of bus, and display a variety of morphological features to facilitate consumption. Observed modifications include increased height and width, decreased length, patterning (including colors consistent with modern automobile manufacturing, asphalt coloring on the lower half to create illusory distance, windshield and passengers, and bumper stickers), and behavioral patterns. As SCP-7539 does not appear to predate the invention of the automobile, the exact development of these traits is still unknown.
SCP-7539 have different environmental preferences and behaviors depending on the type of bus targeted; for instance, instances targeting school buses will often follow them on their route, waiting until all children have been offloaded, and instances targeting tour buses will often congregate around well-known tourist destinations.
SCP-7539 instances do not react to any attempts at communication, or socialize with one other. Given an ample supply of food, SCP-7539 instances do not attempt to escape. When not given food, SCP-7539 instances will become agitated and roam around containment. As SCP-7539 instances will avoid walls, this does not pose a containment breach risk.
If completely drained of gasoline, SCP-7539 instances will no longer be able to move. If completely drained of electricity, SCP-7539 instances will no longer present stimulus-response. The maximum amount of time SCP-7539 instances can go without gasoline depends on travel time, speed, and distance; the maximum amount of time SCP-7539 instances can go without a battery is two weeks. If an SCP-7539 instance is completely drained of electricity and given a full battery, SCP-7539 will not resume stimulus-response. At the time of writing, 1 active instance of SCP-7539 is in containment, from three original captured specimens.
SCP-7539 does not appear to be manmade, though the mechanisms by which a specialized predator could gain a foothold in a roughly one hundred year period is currently unknown.

Footnotes
1. This seeming preference to leave humans unhurt and instead prey solely on other vehicles is the primary distinguishing trait of this anomaly when compared to other organic vehicles such as SCP-3470.

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