Show and Tell

A young boy warns SGC of a plot by invisible non-humanoid aliens (rogue Re'tu, who exist in large numbers on P63-2031) to destroy all humans. A minority of the Re'tu wage war on the Goa'uld by eliminating their potential hosts: humans. They operate in 5-man suicide units, which are capable of setting off an explosion equivalent to a small tactical nuke. SG-1 decide his warning is real, and call the Tok'ra for help, who provide TER's that locate the Re'tus already hiding on the base, and eliminate them.