Stinkhorns, belonging to the fungal order Phallales, are a group of organisms recognizable for two striking features: their unusual physical forms and their unpleasant smell. These fungi are found in forested areas and mulched gardens across the globe, often appearing suddenly. While many mushrooms use the wind to scatter their microscopic reproductive cells, stinkhorns employ a unique, odor-based strategy for spreading their spores. This reproductive method is responsible for the foul stench that earned them their common name.
The Unusual Development and Appearance of Stinkhorns
The life cycle of a stinkhorn begins underground, enclosed in a structure commonly called a “witch’s egg” or volva, which is a round, gelatinous sac. This initial stage, which can persist for days or weeks, is composed of a leathery outer layer, a thick, jelly-like middle layer, and the compressed embryo of the future fruiting body inside. The “egg” stage provides both protection and the stored resources needed for the fungus’s rapid growth.
When conditions are right, the fungus uses immense internal turgor pressure to erupt from the volva, sometimes reaching full size in just a few hours. The mature forms of stinkhorns vary widely, ranging from the common phallic-shaped Phallus impudicus to the latticed, cage-like structure of Clathrus ruber. This rapid extension results in a hollow, spongy stalk that supports a cap covered in a sticky, olive-green or brown spore mass called the gleba.
The gleba is the reproductive surface, and its sticky texture and color are central to the fungus’s dispersal strategy. The mature fruiting body is structurally fragile and short-lived, designed only for the quick deployment of its spore-bearing slime. Once deployed, the entire structure may only last a day or two before collapsing.
The Chemistry Behind the Foul Odor
The intense, fetid odor of the stinkhorn originates exclusively from the gleba, the dark, slimy mass that contains the spores. This smell is a chemical production designed to mimic the scent of decaying organic matter, such as carrion or feces. The purpose of the odor is to attract specific dispersal agents, which is why the smell develops only when the fungus is fully mature.
Scientific analysis of the volatile organic compounds (VOCs) released by a mature stinkhorn reveals a cocktail of chemicals familiar from decomposition. The most significant contributors to the foul smell are sulfur-containing compounds known as dimethyl oligosulfides, particularly dimethyl trisulfide. These same compounds are responsible for the distinctive stench of rotting meat.
In addition to the sulfur compounds, the volatile profile includes substances like phenol and indole, which are associated with the smell of animal waste. This chemical mimicry is highly effective, as the odor is often described as a combination of sewage, rotting meat, and dung, and can be detected by humans from a considerable distance. The “egg” stage releases a much lower concentration of volatiles and is virtually odorless until maturity.
How Stinkhorns Use Smell for Survival
The scent is an evolutionary adaptation for spore dispersal, a strategy known as mycophily. By producing a smell that simulates decay, the stinkhorn attracts insects that specialize in feeding on or laying eggs in carrion and dung, such as flies and certain beetles. These insects are lured in by the promise of a meal or a nursery for their larvae.
When the flies land on the mature stinkhorn, they encounter the sticky, nutrient-rich gleba. They feed on this spore-laden slime, or the slime adheres directly to their legs and bodies as they walk across the cap. The spores are then physically transported away from the parent fungus as the insects move to new locations.
This insect-mediated dispersal ensures the spores are not merely dropped at the base of the fungus. The consumption of the gleba can also have a laxative effect, meaning the spores are often deposited in feces. This provides a nutrient-rich substrate for the spores to germinate, allowing the fungus to spread its genetic material to distant environments.