For the past few days I've had some watermelon rinds placed near my pitcher plants to attract extra flies (both fruit and house.) The tactic has seemed to be helpful, allowing a few more catches than might have happened in the same period without the watermelon. Yesterday, I decided on a little experiment with one of them-- I squeezed a little juice from one of the rinds onto the hood of a pitcher and and into the water inside. Then it rained last night-- I looked today to see if the 2-3 flies that were already in there (plus some termites that I had hand-fed it) had been washed out. And found
this (linked for shock value.)