Jane Hu separates fact from fiction in the non-history of gerbiling:
Not too long after the gay gerbiling rumor made its splashy early 80s debut, Doctors David B. Busch and James R. Starling published a surgical-stats report in Surgery titled "Rectal Foreign Bodies." This 1986 article, which gathered information from prior literature on Rectal Foreign Bodies (or RFOs), is the most frequently cited scientific document when it comes to gerbiling. Busch and Starling tabulated 182 cases by type and number of objects, among which included two whip handles, one plastic rod, one bottle with an attached rope, and one frozen pig's tail. No gerbils, though. Not even a tail.
Hu traces the myth's origin to the AIDS epidemic:
At the start of the 80s, gay men were already perceived as socially and sexually deviant. And if anything is not a secret, it's how especially openly homophobic American culture was throughout this decade. With the addition of AIDS and its attendant narrative of Gay Desires Being Punishable By Death, there seemed to be concerns in the mainstream that maybe gay people, already alienated, weren't being alienated quite enough. Toss interspecies sex with small dirty rat-like creatures into the mix, and you simply get a variation on a theme: gay sexuality as a realm plagued with abnormality, shame-inducing behaviors, and incomprehensible stupidity.