There is a belief that cockroaches will not eat margarine.
only humans are foolish enough to eat [margarine] – rats and cockroaches won’t touch the stuff.
Even the humble cockroach won’t eat margarine.
However this Yahoo Questions answer argues against it.
This seems to be a common urban myth, and seems to be widespread on sites that are dedicated to the latest boogie-man of trans fats.
(A related claim is about ants will eat it, but I am focussed on cockroaches here.)
Do cockroaches eat margarine?