The stinkhorn lures flies with the smell of carrion

The common stinkhorn Phallus impudicus begins as a pale "egg", partly buried in the ground. The mature fruiting body develops quickly, and its head becomes covered with an olive, sticky mass called gleba. The spores are in it. Instead of exposing them to the wind, the fungus produces an intense smell associated with carrion and dung, which brings in flies and other insects.

The odour is not a single compound. Analyses have detected a mixture of volatile substances, including sulphur compounds and molecules giving faecal notes. To a human the effect is repellent; to flies seeking food or a place to lay eggs it is a clear signal. The insects land on the head, eat the slime and smear it on their legs. Spores are carried on their bodies, and some pass through the gut and travel on in their droppings.

The strategy resembles the pollination of flowers, but the reward and the message are the smell of decay rather than nectar. The stinkhorn invests in a moist mass that insects can easily take. Once it is removed, the pale, chambered surface of the head is exposed and the intensity of the smell drops. Speed matters: the fruiting body is short-lived, so attracting many visitors quickly increases the reach of dispersal.

The phrase "lures flies with the smell of carrion" describes a function, but does not mean the fungus decomposes animal remains. It grows as a saprotroph in soil rich in organic matter. Evolution has exploited the olfactory system of insects, offering them a chemical message resembling the resource they seek. It is a good example that for a fungus no smell is "unpleasant" in itself — what counts is the reaction of an effective disperser. Some plants pollinated by flies use a similar principle, but similarity of function does not mean a common origin for their structures or their scent mixtures. In both cases, though, the recipient of the message is the same insect sense of smell.

What the evidence actually shows

The strategy becomes active only when the fruiting body matures. At the tip of Phallus impudicus, a sticky, spore-bearing gleba develops and releases volatiles associated with carrion and faeces. Chemical analysis identified dimethyl disulphide and dimethyl trisulphide as major components; related oligosulphides are also released by decomposing material. Flies and other insects feed on the gleba and move spores externally or after passage through the gut. Work on another stinkhorn, Clathrus archeri, demonstrated chemical convergence between its odour and carrion or dung. The same precise bouquet should not be assigned to every member of the family, because composition varies by species and developmental stage. “Attracts flies with the smell of carrion” describes chemical mimicry, not the production of rotting flesh, and the immature “egg” lacks the mature spore slime and its full emission profile.