[[WMG: The Blog was a deranged [[Series/StarTrekDeepSpaceNine Changeling]].]]
The blob was one of the hundred infant Changelings sent out to explore the Alpha Quadrant. When its vessel crashed on Earth, it was exposed to some substance in the air or soil that induced psychosis and an increase in mass (similar to Odo's experience with a psychotropic gas on L-S VI).