Move over Santa Cruz, we've got our own

There are banana slugs in San Diego County. Banana slugs? Yes, banana Slugs. But wait, there aren’t any banana slugs in San Diego County. Dear reader, let me tell you about the banana slugs of San Diego County.

Banana slugs are very large and are found along the Pacific Coast of North America. Currently, there are six described species with a recorded distribution from northern British Columbia to Santa Barbara and the Channel Islands in the south. They are very well known, well loved by many, and are even the official mascot of UC Santa Cruz.

In San Diego, there were “forgotten” historic records of an isolated population of banana slugs in Palomar Mountain State Park. In 2016, the first iNaturalist observation of the Palomar banana slug was uploaded. Since then, 10 other observations were uploaded from the same small area of Palomar Mountain—in fact, the third observation of this population was by our very own Vice President of Science and Conservation Kevin Clark. The “rediscovery” of the banana slug from Palomar Mountain sparked a lot of interest with the local malacologists, or mollusk scientists (yes, slugs are mollusks).

There are two hypotheses about the population of banana slugs of Palomar Mountain:

1. It is an introduced population that came from an existing species farther north. Perhaps it was transported to this area when a small dam was built.
2. It represents an undescribed “relict” species that somehow has persisted on Palomar Mountain but not on any of the surrounding mountains in Southern California.

To determine which hypothesis is correct, researchers from the Natural History Museum of Los Angeles County and CSU San Marcos teamed up to try and find some specimens to conduct genetic work. They attempted to find a specimen from Palomar Mountain a total of 8 times and were not successful. At the recent SCUM (Southern California Union of Malacologists) meeting held at The Nat, they briefly mentioned their attempts to find the slug. Curator of Invertebrate Zoology Shahan Derkarabetian then told them about our existing arachnid-based projects on Palomar Mountain in that same exact area. That's when Invertebrate Zoology team joined forces with them to help look for the slug.

After their many previous unsuccessful attempts, on the first collaborative trip to Palomar in April of 2026, Shahan found a single specimen! Check it out in the photos below. Much excitement followed. This specimen is currently being used for both genetic and morphological work and is deposited in the Invertebrate Zoology collections. Those tissue samples are actively being used for barcode and whole genome sequencing.

Is this Palomar Mountain population a new species? It just might be. Stay tuned!

Posted by Shahan Derkarabetian, Curator of Invertebrate Zoology.