"It's another form of diversity the vast majority of public does completely overlook."
— Bill Leonard
Blame it on the carnivorous snails.
Those predatory mollusks have a healthy appetite, and they’ve got a taste for the slugs of western Washington. To escape the snails, many gastropods turn to unique methods of defense. And you’ll find a true fighter in the jumping slug.
Secretive, mysterious and often overlooked, the jumping slug can be found around forested areas throughout Washington, including the Conservancy’s Ellsworth Creek Preserve.
Researchers believe our state is actually the center of biodiversity for jumping slugs, with at least five species including the warty jumping slug (Hemphillia glandulosa), the keeled jumping slug (H. burringtoni) and Malone (H. malonei). Of the group, the dromedary jumping slug (H. dromedarius) is the Olympic gold-medal jumper.
When a snail or other predator moves in to take a bite out of one of these guys, it performs its signature move – the one that earned it its name.
“It’s really not jumping, it’s more like corkscrew motion. They tighten up, coil up and straighten out rapidly,” said William Leonard, a Washington resident who has contributed to numerous books and papers on invertebrates.
He says jumping slugs are the only land gastropod in the United States known to exhibit this acrobatic behavior.
A Mystery Slug
When many people think about slugs, they think of the exotic slugs that were introduced into our ecosystem and forage in our gardens. Jumping slugs are native to the Pacific Northwest.
Researchers say many things about these mollusks remain a mystery, including the exact number of species and their relationship to other gastropods.
“They’re fascinating windows into lots of different questions about biology and nature,” Leonard said. “It’s another form of diversity the vast majority of public does completely overlook. “
Larger varieties – like the Malone jumping slug or pale jumping slug – can reach lengths of an inch and a half when fully extended. They have one unusual feature: a hump on their backs. Snails carry their internal organs hidden inside their shells; most slugs hide them within a cavity in the foot. But the jumping slug is caught in the middle – carrying their internal organs in a hump on their back. It has a partially exposed shell that’s been compared to the human appendix (i.e. it has no function).
Seven species of jumping slug have been described in the Pacific Northwest, throughout Washington, Idaho and Montana. But researchers say there are more out there.
“If a person really got down and did the DNA analysis on these, they’d probably find there’s more species than described,” said Tom Burke, a retired Washington resident who is working with Leonard to publish a field guide on land mollusks.
The existence of one variety of jumping slug, the panther, remains uncertain; only one specimen has been collected—and that was back in the 1970s.
Might as Well Jump!
Jumping slugs existed largely under the radar until 1994, when the Northwest Forest Plan was adopted. Leonard says this plan brought conservation and management of invertebrates into the mainstream.
He became interested in jumping slugs during his career as a wildlife biologist.
“The thing really got me hooked was working on these surveys 10 years ago and going out to do surveys for transportation projects on Forest Service lands,” Leonard said
It’s rare to see the jumping slug jump in the wild. In a resting posture, they curl their tail around to the side – appearing ready to jump. But you’d have to hold one in your hand to see it in action.
“If you take one and put it on your hand it might just sit there a little while,” Burke said. “Once they get irritated they just start flopping and they’re off your hand in just a second, you know. More like they’re just writhing around like a fish out of water. They just flop around.”
If they were trying to escape a predator on a piece of bark or log, that flopping behavior would allow them to lose their grip on the log and flee by tumbling away.
“So it’s immediately separated from the snail,” said Leonard. “The second thing, is it breaks the slime trail. These snails and slugs – they do have some vision ability – but it’s believed their sensory world is largely olfactory taste and smell. With the slime trail broken, there’s no way of knowing where it’s disappeared to.”
Though often overlooked, jumping snails have a lot to offer.
“They eat living and decomposing vegetation. They’re kind of recyclers. They also are thought to be potentially important dispersal agents for fungal spores,” Leonard said.
And aside from predators like snails, beetles and salamanders—their only threat is the loss of habitat. Jumping slugs rely on Washington’s forests to thrive.
“It’s another form of diversity the vast majority of public does completely overlook,” Leonard said. “Birds are obvious. They’re conspicuous – people appreciate them for beauty as much as ecological benefits they bring. Snails and slugs are just as important from an ecosystem function standpoint, but in their own way just as beautiful and even more diverse.”