Flanders Moss NNR
I met a fellow traveler the other day on the path around Flanders.
The black slug (Arion ater) is a very common invertebrate, we see them almost every day when it is warmer but despite seeing it so often I realised I knew very little about it.
So if you want to know more about black slugs, especially their mucus, read on. Firstly they are very common and successful. This is partially because they eat just about anything. Their diet can include carrion, fungi, earthworms, leaves, plant stems, dead plants and dung. In our family they are called dog poo slugs as you can often find them wrapped around the afore mentioned object.
They eat these things but using their radula – this is a mouth part structure that is like a belt sander – a very rough strap that grinds off fragments of food that are then ingested and broken down with enzymes. Seeds and spores that are eaten whole can then be transported around a habitat and spread through the slug’s waste. As decomposers and consumers their diet makes them a very important in an ecosystem as part of the waste disposal system that breaks down plant and animal remains. This ability to eat lots of different things also means that they can be used to monitor pollutant levels in an ecosystem, for instance mercury levels.
They tend to be more active at night and this individual seen early in the morning was obviously heading back home after a busy night. It looked rather uncomfortable as it slid rather gingerly over the hard gravel. Its movement was helped by quantities of thick mucus that it secretes on its underside to ease its passage. Black slugs actually produce 3 types of mucus, a finer one around its sides and back which helps to stop it from drying out and another that tastes vile to prevent predation. Apparently in Sweden in the 18th century this mucus resulted in slugs being used extensively to lubricate cart axles, which seemed a bit harsh on the slugs.
The slug looked so uncomfortable that I was tempted to help it across the path. But I didn’t as when other slugs come across a mucus trail the follow it so they can mate. so if I had moved it I might have spoiled a special slug moment. Instead I left it to continue on its travels but it had added to my day by encouraging me to find out just what interesting these creatures are, despite first appearances.