Environment

As Droughts Worsen, What will Become of UCSC’s Slimy Icon?

While wet weather will entice buried slugs back to the surface, persistent drought still poses a threat to slug populations.

Even scientists are having trouble spotting banana slugs these days, according to Janet Leonard, a research associate and banana slug expert at UCSC.

By Guananí Gómez-Van Cortright

“Welcome back slugs!” proclaim banners in downtown Santa Cruz as UCSC students return to in-person classes. But the slimy critters behind the school’s mascot are becoming a rare find on the dusty trails beneath the redwoods.

Even scientists are having trouble spotting banana slugs these days, according to Janet Leonard, a research associate and banana slug expert at UCSC. Last winter, Leonard tried to collect banana slug species in Big Sur, a typically reliable site.

“In three trips I found three slugs,” she says.

Despite being squishy and porous, banana slugs are quite resilient. In experiments, they were able to withstand losing as much as 30% of their body weight through dehydration and still recover. But over the last 40 years, California droughts have been getting longer and more severe, straining majestic old-growth and slow gastropods alike.

According to Leonard, banana slugs seek shelter from dry conditions by burrowing underground in search of wetter soil. Their quest for moisture can be extreme: banana slugs have been found as deep as nine feet underground. While wet weather will entice buried slugs back to the surface, persistent drought still poses a threat to slug populations.

The survival of banana slug eggs has Leonard especially concerned.

Banana slugs lay eggs at the start of the rainy season in leaf litter, a layer of rotting plant material piled on the forest floor. The eggs need to spend seven to 10 weeks enveloped in a moist layer of leaf litter in order to successfully hatch. This is the most vulnerable time in a slug’s life; if there isn’t enough rain to keep the forest floor moist during those weeks, the eggs will shrivel before the young slugs have a chance.

“I don’t think these populations are extinct, but I do think after a second year of drought there is going to be an effect on the population, and it’s going to decrease,” Leonard says.

Banana slugs’ deep burrows make it hard to tell how many may be hiding out of sight beneath the forest floor. This is why there have not been any official population counts for banana slugs, Leonard says, and there has been no published research comparing banana slug populations to moisture levels. While the lack of population counts makes the fate of banana slugs tough to track, Leonard thinks they are a useful indicator of current moisture in the environment and the effects of drought.

“When you’re not seeing as many on the surface as you typically do, that tells you that the drought is having an impact,” Leonard adds.

While redwood trees are able to endure several years of drought and can even recover after being damaged by fire, banana slugs are a far more fragile piece of the temperate forest puzzle.

“It’s important to remember that slugs may just be little invertebrates, but they play an important role in the forest,” says Leonard.

The UCSC Slugs may have returned to campus, but the dwindling presence of banana slugs serves as a slimy reminder of just how much the redwood forest and its residents rely on winter rainfall.

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