By Victoria Metcalf 04/03/2016

Sometimes we find quite extraordinary, yet ordinary, things in our own backyard. Introducing a slug.

The other day I found this beauty sliding along our doormat.

Slugs and snails don’t gross me out. After all, thanks to an interest shown by Miss6, we kept Big Gavin, a hand-me-down snail and his/her friends for nearly 2 years as a pet. Big Gavin eventually escaped with numerous babies, friends and family members when Acorn our pet house rabbit caved in the mesh on their home.

I’m not averse to getting rid of the slimy critters either – neem granules seem to work to some degree to stop them decimating the veges. Or alternatively putting them over the fence.

But despite that we still have some mucus-y movers.

I certainly wasn’t expecting though to see a 10cm long slug -at first glance looking like, well a turd, on our mat. I didn’t know we had such big slugs in New Zealand. This isn’t a native, but is what’s known as a yellow cellar or garden slug, scientifically known as Limacus flavus a subgenus of Limax flavus. Limax/Limacus are air-breathing nocturnal land slugs (in technical terms my find is a terrestrial gastropod mollusc), known as keel-back slugs. You can see its breathing hole in the pics.

The slug was over 10cm long when on the move.
The slug was over 10cm long when on the move.

The yellow garden slug

They’re found in lots of places around the world through accidental introductions, including North America and New Zealand, but are native to Southern and Western Europe. They are not always so yellow (or anaemic looking as one person on Twitter put it), but my one was apparently very typical colouring. As they are usually only active at night and they like damp places, it’s common not to see them and therefore to realise how abundant they are. The yellow garden slug feeds mainly on decaying material, fungi, and in bad news for us home vegetable growers, also vegetables.

Mucus mayhem

We’re probably all familiar with the fact snails and slugs move around on a layer of mucus that they are constantly producing. Hence the glistening silvery snail (or slug) trails we see in the morning in the garden. The mucus is lubrication to allow the muscular contractions on the underside of its foot to propel it along. They also produce a second kind of mucus to coat its body to stop it drying out.

What amazed me, however, was just much mucus our mellow yellow slug pumped out. I expected it at any point to shrivel into nothingness based on its slime production rate. But the slug stayed gargantuan.

The foot mucus of snails and slugs is actually a liquid crystal (or gel) polymer (watch a cool video here). What I didn’t know is that the slime is both glue at rest and liquid when stress is applied and this is what allows the slug to crawl up walls without falling off.

Repetitive task, a T-shirt design by Nacho Diaz and available from Threadless Designs.
Repetitive task, a T-shirt design by Nacho Diaz and available from Threadless Designs.

The mucus was also unbelievably sticky and glue-like. Normal soap and water washing failed to remove it. It took at least four washes and a lot of scrubbing to remove the adherent material. It might have its uses- researchers have been looking at snail or slug slime for some time in the field of biomimetics (mimicking biology) – to look at improving drug delivery systems, or in producing lubricants.

I know snail mucus extract is also a popular facial treatment and it seems it is also used in cosmetics production. I felt no compulsion though to let our yellow slug roam on my face in the quest for beauty.

Close up of the slug showing it's two pairs of tentacles, breathing hole and fingerprint pattern on its back.
Close up of the slug showing its two pairs of tentacles, breathing hole and fingerprint pattern on its back.

Like most land slugs, this one has two pairs of tentacles which you can see in the pictures. The upper blue-ish and longer pair are called optical tentacles and they can sense light.  The lower, shorter pair are oral tentacles, used for smell. Both pairs can retract to avoid hazards and if lost to predation or other hazards, the slug can regenerate them.

In potentially bad news for our vegetables it can lay 12 to 32 eggs per clutch with each egg 5-6 mm.

Many of our escaped snails may still be resident in our garden.  The mellow yellow cellar slug is however, hopefully well away over the road. Who knows though, it may have left friends or family members behind.

Have you seen one of these?

0 Responses to “Slugging it out? They call me mellow yellow”

  • Is that the optic nerve (or equivalent) you can see travelling along the optical tentacle and into its body? Really cool. The pupil in your last photo reminds me of a praying mantis’ psuedopupil but I guess because this slug doesn’t have compound eyes that can’t be what it is.

    • I am thinking it must be the optical nerve or similar. As far as I am aware no compound eyes in a slug- just ability to sense shadows and change in light.