Nothing to Declare
S16 E8 Suspicions arise when officers locate bags full of designer goods, and biosecurity does not waste a minute fooling around with a Mongolian delicacy in a passenger's luggage.
Star Trek: Deep Space Nine
S4 E7 Little Green Men While taking Nog to Starfleet Academy on Earth, Quark's shuttle malfunctions and crashes in Roswell, New Mexico, in the year 1947.
Stargate SG-1
S6 E13 Sight Unseen Civilians manage to see a species of harmless insects that have always been present on Earth but living on a different astral plane, in principle supposedly invisible to humans. SG-1 must find a way to stop this phenomenon.