The following post was written by Woodlore’s Aspirant Instructor and Quartermaster, Keith Whitehead:
During our many months spent in the field, we have the chance to see much wonderful wildlife and most of it is a joy to behold. There are some exceptions to this rule however, and racing its way to the top of most people’s lists of unwelcome visitors is the humble slug.
At this point you may be expecting me to extol the edible virtues of this creature in order to curry favour for the unpopular pest, but in truth they are best avoided; if you want a meal, put them on a hook and use them as bait. There is more to the average slug than meets the eye though and a recent encounter prompted me to investigate a little further.
On seeing a slug gently pulsating its way towards my mug, I would normally remove the slug/mug and think no more about it, but this time I decided to see how it used its two pairs of tentacles to locate and recognise food. I knew that the upper pair of optical tentacles were sensitive to light but that they did not recognise colour and that the lower sensory tentacles recognised chemicals in much the same way as our sense of smell. To test this I presented the slug with some food (the closest thing to hand being a biscuit) and watched. As soon as the sensory tentacles brushed the biscuit, the slug veered from its course and proceeded to gorge itself. It’s not often that you find out you have something in common with a mollusc.
The slug in question is a member of the Arion genus, probably Arion ater (black slug) although this is difficult to differentiate from other members of Arion without dissection. Despite its common name, the colour of the ‘black slug’ varies considerably, this example being an orange/brown. Its mouth can be clearly seen in the photograph, the margins looking like a row of blunt teeth. These are not used the chew the food however. The slug is a mollusc and as such, uses a radula to grind its food. This organ is best likened to a tongue made of cartilage and covered with up to 27,000 chitin teeth. This is used to rasp food into the mouth in a backward and forward motion. Black slugs are omnivores and, as well as biscuits, they will eat vegetable matter, fungi, dung and carrion.
Watching this animal feed, seeing it close up and reading about its biology and behaviour garnered new respect for an old adversary, and I would advise anyone to delve deeper into things that are normally overlooked. The process of researching often takes you down unexpected avenues and is a joy for those who are interested. I have only touched on a couple of the fascinating things that I learned during my investigations and the purpose of this article is to encourage others to look, observe and research. A good start and aid to identification of terrestrial molluscs can be found at the ID Tools website.
The next time I encounter one of these creatures on/in my mug, shoes, water bottle or face, at least I will be respectfully disgruntled rather than completely outraged.
– Keith Whitehead