In the spring, blooming flowers create a picturesque background anywhere you look. Ultimately, all things come to an end, and many of the flowering trees have already shed their petals as new buds grow. Less regrettably, however, is the dissipation of the trademark scent of these smelly white trees.

However, these smelly trees, or callery pears, hold a surprisingly sinister secret. As if their infamously pungent odor wasn’t enough, the trees are also considered an invasive species in many parts of the US.

Although callery pears are common throughout San Ramon and the US, they are actually native to parts of East Asia. During the 1900’s, the callery pear became popular as an ornamental tree in American cities due to its beautiful foliage, resilience, and sterility. Over time, the callery pear’s major weakness became apparent: poor branch structure. Its production of densely-packed upright branches left it susceptible to splitting and damage during storms. To overcome this flaw, breeders developed cultivars such as “Aristocrat” and “Chanticleer” with better branching habits.

However, this short-sighted action had unforeseen consequences, namely increased genetic diversity. Due to breeding and the creation of genetically different cultivars, callery pears gained the ability to produce viable fruit. From then, the trees spread profusely, often crowding out native species.

The severity of the invasion varies throughout the country, with several eastern and midwestern states labeling the callery pear as an invasive species.

Not everybody knows about the destructive nature of these trees, but nearly anybody can describe their putrid smell. The scent produced by callery pears has often been compared to rotting fish, which is unsurprising since both contain similar compounds.

Richard Banick, a botanical manager at Bell Flavors & Fragrances, attributes the smell to volatile amines such as dimethylamine and trimethylamine.

As reported by the U.S. National Library of Medicine, dimethylamine and trimethylamine are present in fish and other seafoods. In low concentrations, both chemicals have a distinctively fishy smell.

Although the smell may be revolting, it is actually a boon to the trees. Dr. Eloy Rodriguez, a professor of plant biology at Cornell university, surmises that the volatile amines produced by the flowers actually attract pollinators. Consequently, the trees only produce the chemicals when they are flowering, explaining why the air smells terrible around March. This evolutionary perk is an unpleasant reminder that one man’s trash is another man’s—or insect’s—treasure.