Scientists Uncover the Unexpected True Identity of “Tequila” Worms

Jul 25, 2023

By Florida Museum of Natural HistoryApril 18, 2023

A study published in PeerJ Life & Environment analyzed the species of larvae found in bottles of Mezcal, a distilled alcoholic beverage made from agave. Somewhat unexpectedly, the study found that all the larvae were of a single moth species, C. redtenbacheri, which is one of the most commonly consumed edible insects in Mexico.

Mezcal is a distilled spirit produced from the cooked and fermented sap of agave plants. The majority of mezcal drinks, including all tequila varieties, are marketed as unadulterated distillates, but a select few contain an unexpected addition: worms.

Referred to as gusanos de maguey in Spanish, which translates to agave worms, these peculiar accompaniments are not truly worms, but rather a kind of insect larva. The practice of incorporating these larvae into mezcal is relatively recent, as mezcal production boasts a rich history that traces back to the earliest Spanish settlers in Mexico. However, it wasn't until the 1940s that larvae were first introduced to the beverage.

Since then, gusanos have helped boost the popularity of mezcal, but their identity has remained elusive. There's no consensus on what type of larva is used in mezcal or even if it belongs to one or multiple speciesA species is a group of living organisms that share a set of common characteristics and are able to breed and produce fertile offspring. The concept of a species is important in biology as it is used to classify and organize the diversity of life. There are different ways to define a species, but the most widely accepted one is the biological species concept, which defines a species as a group of organisms that can interbreed and produce viable offspring in nature. This definition is widely used in evolutionary biology and ecology to identify and classify living organisms." data-gt-translate-attributes="[{"attribute":"data-cmtooltip", "format":"html"}]">species. They’ve been variously ascribed to moths, butterflies, and even a type of weevil.

"It's relatively easy to broadly determine the kind of larva based on the shape of the head, but their identity has never been confirmed," said Akito Kawahara, curator at the Florida Museum's McGuire Center for Lepidoptera and Biodiversity. "This is probably because most biologists are not looking inside mezcal bottles."

Mezcal is made from the boiled and distilled sap of various agave species. Credit: Charles Lemaire

In a new study, recently published in the journal PeerJ Life & Environment, Kawahara and his colleagues decided to pin down the identity of the mezcal gusanos. In 2022, they traveled to Oaxaca Mexico, which has been the center of mezcal production for hundreds of years. There, they visited distilleries and obtained as many different brands as they could find to ensure a diverse sampling of larvae.

There were very few distinguishing features that could be used to assign the specimens to a particular group or species; fortunately, mezcal makes an excellent preservative, preventing the decay of the larvae and their internal packets of DNADNA, or deoxyribonucleic acid, is a molecule composed of two long strands of nucleotides that coil around each other to form a double helix. It is the hereditary material in humans and almost all other organisms that carries genetic instructions for development, functioning, growth, and reproduction. Nearly every cell in a person's body has the same DNA. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is called mitochondrial DNA or mtDNA)." data-gt-translate-attributes="[{"attribute":"data-cmtooltip", "format":"html"}]">DNA. The researchers successfully extracted and analyzed genetic material from 18 specimens, but the results they got back were unexpected.

Mezcal is a type of distilled alcoholic beverage that is made from the agave plant, which is native to Mexico. It is similar to tequila but is made from a wider variety of agave plants and is typically produced using traditional methods such as underground pit ovens and stone mills.

Since gusanos de maguey aren't commercially farmed, the authors suspected that mezcal worms would likely be sourced from several unrelated species. This included a type of butterfly called the tequila giant skipper (Aegiale hesperiaris), which lays its eggs on agave plants. Their large, milky-white caterpillars parasitize several agave species, boring tunnels through the rigid, succulent leaves. The eponymous common name, combined with their white larvae — which match the color of many gusanos de maguey — marked them out as a primary suspect.

Instead, the DNA unequivocally identified all 18 specimens as the caterpillars of agave redworm moths (Comadia redtenbacheri), another type of agave parasite with rosy-hued larvae. The researchers suspect that accounts of white gusanos de maguey come from caterpillars that have been stored in alcohol for long amounts of time and have consequently leached their color.

The results add a sobering note to what is currently a boom in the international popularity of mezcal. According to a report by Straits Research, an independent analytical firm, the sale of mezcal is expected to increase by 22% in the next decade, reaching $2.1 billion in profits by 2030, riding a growing wave of interest in artisanal, ethically manufactured products.

Unlike tequila, which is mass-produced in industrial autoclaves, mezcal production continues to rely on small-scale facilities in Mexico's arid countryside. Farmers roast the barrel-shaped agave cores in open fire pits or specialized kilns, then chop and pulverize the crisp stumps for fermentation and small-batch distribution. It's unclear whether all mezcal distilleries and landowners will be able to sustainably scale up production to meet demand.

The fate of agave redworm moths is also uncertain. Maguey worms have been harvested as a delicacy for centuries, beginning with the Aztecs. But demand for the larva in Mexican culinary establishments has also seen an increase in recent years, to the extent that wild populations of these caterpillars are considered at risk of overharvesting.

"Agave worms are still fairly common, but the impact of mezcal becoming popular can have long-term negative effects on local populations because they are harvested in the wild," Kawahara said.

Red agave caterpillars burrow deep into the core of their host plants, and collecting them often kills the agave. For production to scale with the growing market, it's possible local harvesters may need to actively grow caterpillars on agave farms or find ways to produce them outside of their host plants.

For more on this research, see Mezcal Worm in a Bottle: DNA Testing Yields Unexpected Results.

Reference: "Mezcal worm in a bottle: DNA evidence suggests a single moth species" by Akito Y. Kawahara​, Jose I. Martinez, David Plotkin, Amanda Markee, Violet Butterwort, Christian D. Couch and Emmanuel F.A. Toussaint, 8 March 2023, PeerJ.DOI: 10.7717/peerj.14948