Mezcal “Worm” in a Bottle Mystery: DNA Testing Reveals a Surprise

That strange "worm" at the bottom of some mezcal bottles has finally been identified. The answer overturns decades of guesses.

Mezcal is a spirit with deep roots in Mexican culture. Producers cook the agave plant, ferment it, and distill it. Most bottles are clear, pure distillates. However, a small number contain a larva at the bottom.

These famous "worms" are called gusanos de maguey, which means agave worms in Spanish. They are not worms at all, but insect larvae. They became part of the mezcal story much more recently than the drink itself. Mezcal production dates back to the early Spanish presence in Mexico. But larvae did not appear in bottles until the 1940s.

Identifying the Mezcal "Worm"

For decades, the gusano helped make mezcal more recognizable, especially outside Mexico. Yet, no one knew exactly what it was.

Different ideas pointed in different directions. Some thought the larvae were moths. Others suggested butterflies or even weevils. It was not clear if producers used one species or several.

Akito Kawahara, a curator at the Florida Museum’s McGuire Center for Lepidoptera and Biodiversity, noted that it's usually easy to tell the type of larva by its head shape. However, their identity was never confirmed. He believes this is because most biologists don't look inside mezcal bottles.

To solve the mystery, Kawahara and his team used DNA. Their study, published in 2023 in PeerJ Life & Environment, looked at larvae from mezcal bottles sold commercially. In 2022, the team went to Oaxaca, Mexico. This is a key region for mezcal production. They collected many different brands to get a wide range of gusanos.

DNA Reveals the Truth

The larvae offered few physical clues. After soaking in alcohol, many had lost features that could help identify them by sight. But the mezcal had preserved the specimens and their genetic material.

The researchers successfully extracted and analyzed DNA from 18 larvae. They expected to find different species. Gusanos de maguey are not farmed, so it seemed likely that producers would gather larvae from various insects living on agave plants.

One strong suspect was the tequila giant skipper (Aegiale hesperiaris). This butterfly's caterpillars eat agave. Its large, pale larvae tunnel into agave leaves. Their whitish color matched many of the preserved gusanos in bottles. The name also made it seem like an obvious choice.

But the DNA showed something different.

Every larva that provided usable DNA matched the agave redworm moth (Comadia redtenbacheri). The specimens that didn't amplify successfully were also identified as the same species by their appearance.

This means the famous mezcal "worm" is much more specific than many thought. The samples all pointed to the caterpillar of one moth, not a mix of agave-eating larvae.

The finding also explains why the larvae's color was confusing. Agave redworm moth larvae are naturally rosy or reddish. But many gusanos de maguey in bottles look pale. The researchers believe that long exposure to alcohol may bleach the larvae over time, making red caterpillars appear white.

Sustainability Concerns for Mezcal and Moths

This discovery comes as mezcal's global popularity grows. A report from Straits Research predicts mezcal sales will rise 22% over the next decade. They could reach $2.1 billion in profits by 2030. This growth is partly due to demand for artisanal and ethically made products.

This growth creates a complex challenge. Tequila is often made on an industrial scale. Many mezcals, however, still come from smaller rural operations in Mexico's dry countryside. Producers roast thick agave cores in pits, crush the plant material, ferment it, and distill it in small batches.

Scaling this tradition is not simple. It's unclear if mezcal producers, landowners, and agave farmers can increase output sustainably. They also need to preserve the ecosystems and practices that make the spirit unique.

The agave redworm moth also faces pressure. Maguey worms have been eaten in Mexico for centuries, dating back to the Aztecs. More recently, demand from restaurants and specialty food markets has grown. These caterpillars are usually collected from the wild. Researchers warn that local populations could be overharvested.

Kawahara noted that agave worms are still common. But the popularity of mezcal could have long-term negative effects on local populations because they are harvested from the wild.

Harvesting can also harm the plant. Red agave caterpillars burrow deep into the core of their agave hosts. Removing them often damages or kills the agave itself. If demand keeps rising, harvesters may need to raise caterpillars on agave farms. Or they might need to find ways to produce them without relying entirely on wild plants.

Recent research highlights these sustainability concerns. A study on chinicuil extraction and ixtle maguey populations found that harvesting Comadia redtenbacheri larvae can reduce Agave applanata populations by up to 57%. The study also found that young agaves are crucial for population survival. Yet, these are often the plants harvested for larvae.

This work looked at a different use of agave, not bottled mezcal specifically. But it shows the same biological problem. When larvae live inside agave, collecting them can mean sacrificing the plant that supports them. The 2025 study recommended responsible management to protect ixtle maguey populations threatened by chinicuil extraction.

The mezcal worm is a marketing icon, a culinary tradition, and a scientific curiosity. DNA has now clarified what it is. The harder question is how to keep this tradition from putting too much pressure on the moths and agaves that make it possible.

Deep Dive & References

Mezcal worm in a bottle: DNA evidence suggests a single moth species - PeerJ, 2023