30 Days Wild - Day Twenty-four - Solve a wildlife puzzle

By Barbara Cracknell

An intriguing find for 30 Days Wild...

I was happily weeding in my garden and disturbed this slug. Whilst slugs are not one of my favourite creatures this one fascinated me! I couldn't make out what was on its back or on the end of its tail so I reached for my camera and took some photos. I was surprised to find that a spider was hitching a ride, I wondered whether this was normal animal behaviour? I am also not sure what was on its tail. It's so surprising what you can find in your back garden!

A spider appears stuck on a slug crawling on a wall

By Barbara Cracknell

An answer...

Our Chief Executive Brian Eversham, slug expert and enthusiast, took a look at the image and has this to say:

"The ‘what’ is straightforward, the ‘what are they doing?’ is a little more tricky.

"The slug looks like a Great Red Slug, Arion rufus, which is one of the round-backed slugs. These characteristically have a mucus gland above their tail tip (hence the rather disgusting blob at its rear end). 

"The spider looks most like one of the leaf-curling sac spiders, Clubiona, but I think it is both a youngster (hence smallish size and small wide-spaced eyes), and has recently shed its skin, hence unusually pale. The family are typically large and thickset, and have large dark jaws. 

A Clubiona spider

Clubonia spider by Brian Eversham

"I am also puzzled as to why the spider is there: its legs are in a rather unnatural position, which suggests that it’s stuck in the slime (large Arion slugs have particularly adhesive mucus), so it might simply have walked on the back, not realising It was a slug. I’ve never come across spiders feeding on or drinking the slime, nor would they try attacking a slug (the slime is a strong deterrent, and slugs probably don’t move fast enough for a spider to register that they are animals!). 

A close-up view of a harvestman trying to feed on a finger

Harvestman trying to feed on Brian's finger

"You do occasionally see harvestmen (aka harvest-spiders) feeding on slime: they pick at their food with a pair of chelicerae, which are like jaws on jointed extensions – this one was trying to eat my finger.

"Harvestmen recognise potential food by smell and taste rather than watching for movement, and they’d also forage on dead slugs and snails, unlike true spiders."

Day 24 icon for 30 Days Wild


Ways to go wild...

Solve a wildlife puzzle. Found something you're not sure about? Behaviour not mentioned in your field guide? Try putting your query to the friendly online community of experts and enthusiasts via social media. Use the hashtag #lovewildlife or #wildlifetrusts and see what answers come back to you!