These must have been the larv of a blowfly similar to that which has been mentioned by others as inhabiting Sarracenia.
The house-fly has a life-history and immature stages like the blowfly, but its eggs are deposited on manure.
He swore savagely under his breath, and dabbed viciously at a blowfly that suddenly became noisy on the window-pane.
He had eased his uncle's labours by crushing the wasp, and averted his aunt's displeasure by obliterating the blowfly.
A blowfly crawled over a caribou carcass, and possibly a few black flies were abroad.