Slug Situation Under Control in the Huntington Conservatory

The Huntington’s Botanical staff members routinely collaborate with other institutions and agencies to tackle conservation challenges.

By Sandy Masuo

Most of the time, these are carefully planned projects: propagating rare and endangered species, making gardens more resilient to the changing climate, and teaching such techniques as cryopreservation or culturing plant tissue. But sometimes, the unexpected happens.

In December 2022, visitor Jake Garcia spotted an unusual slug in the Huntington’s Conservatory for Botanical Science. He snapped a photo and posted it on the community science platform iNaturalist with his conjecture that it could be a slug in the Veronicellidae family—leatherleaf slugs. Jann Vendetti, associate curator of malacology (mollusks) at Los Angeles’ Natural History Museum and an administrator on iNaturalist, responded: “That would be a very unusual slug for Southern California. Do you have more information?” Once Vendetti confirmed that the slug was indeed Veronicella cubensis, a very problematic invasive species from the Caribbean, she alerted Huntington staff.

In response, Huntington closed the Conservatory to the public and assembled a containment team of botanical staff, scientists from the University of Hawai‘i, and representatives from the California Department of Food and Agriculture (CDFA) and the University of California Division of Agriculture and Natural Resources.

Not all introduced species are considered invasive. But in a hospitable setting, invasive species can wreak havoc, destroying agricultural crops, displacing native species, and potentially spreading new pathogens.

Since this slug thrives in the tropics, it probably couldn’t establish a population in California outside of greenhouse conditions. Nevertheless, the slugs in the Conservatory needed to be contained as quickly as possible.  Fortunately, the Conservatory’s controlled environment made that process easier.

Strategies for containing V. cubensis at The Huntington included removing mulch produced in-house and replacing it with commercial mulch, which is routinely sterilized. Heating mulch to 122 degrees Fahrenheit is 100% effective at killing slugs and their eggs. The Huntington acquired a low-pressure steam generator to sterilize any future mulch produced on the grounds.   A variety of essential oils—particularly clove bud oil—are highly effective at killing the slugs and their eggs. These oils break down relatively quickly, thus avoiding long-term toxicity Routine monitoring continues, with Vendetti assisting in specimen identification.

Before the Conservatory can fully reopen, the California Department of Food and Agriculture requires assurance that the risk of a wider infestation is negligible. Thanks to diligent monitoring and control measures, the V. cubensis population has shown a steady and significant decline, with only stray individuals remaining.

Corpse Flower Will Be On Display

Although the Conservatory remains closed, CDFA officials are confident that Huntington staff has the situation well in hand and approved a plan to open a restricted section of the building to display this season’s Corpse Flower (Amorphophallus titanum). Updates regarding the Conservatory, including a reopening date, will be posted online.

Sandy Masuo is the senior writer in the Office of Communications and Marketing at The Huntington. This article has been edited for clarity and brevity.