On the streets of Hanoi, a select few food stalls offer a coveted condiment: cà cuống essence. The expensive extract comes from an increasingly rare water bug (Lethocerus indicus) whose pungent aroma will make a snack of steamed rice rolls an unforgettable experience.

Although it is billed as water bug “essence,” it is in fact the pheromone that the male bug uses to attract the female during mating season. The pheromone gets extracted from a tiny, liquid-filled sac in the insect’s back by hand in a laborious process. More than 2,000 male water bugs are needed to produce 25 milliliters of the essence. The resulting flavoring agent, which has a funky yet floral aroma, is added to a variety of Northern Vietnamese soups and broths. Bear in mind, though, that the real deal is pricey, so a synthetic version is the commonly-used household favorite. Traditionalists, however, still prefer splurging on the actual water bug essence, which is said to be a strong aphrodisiac. But don’t go overboard: Some say that eating too much of it will make your mouth go numb.

The best use for cà cuống is arguably to flavor the dipping sauce that accompanies bánh cuốn, paper-thin steamed-rice rolls that are a popular Hanoi breakfast food, sold in street food stalls. It is also a flavor enhancer for chả cá lã vọng, a sautéed dish that combines fish with a heap of onions, dill, and other herbs.

Pollution, urban encroachment on farmland, and the use of pesticides are considered the leading causes for the rapid disappearance of the water beetle. Some even say that the biochemical effects of the Vietnam War may have been a cause. The good news, though, is that some Vietnamese biologists have made bringing the water bug back to its habitat a part of their research agenda. Projects to train villagers in resource-poor regions to farm the insects are generating income and reviving a lost culinary tradition.