ANYTHING in the nature of acrobatics would hardly be accredited to slugs and snails; nor indeed does one ordinarily associate them with spinning, an industry of which the monopoly is usually believed to be held by spiders, and to a lesser extent by certain caterpillars. Nevertheless, although they do not perform these things as a matter of habit, certain slugs are capable on occasion of spinning threads and suspending themselves from the branches of trees, or even of swinging from one branch to another. The material used in the spinning of such threads is the same as the mucus given off from the body as the slug travels over the ground and which gives rise to the tell-tale silvery tracks. The significance of this form of spinning is obscure, but in some cases it is associated with mating, the two slugs hanging suspended side by side and mating in mid-air.
An example of spinning may be seen in the bladder-snails living in ponds and streams. They often spin a thread a foot or more in length and reaching from the surface of the water to the bottom, or with the lower end hanging free. A few inches of the upper end of the thread are allowed to lie free on the surface to give the necessary grip. With the thread in position the snail can travel from the bottom of the pond to the surface and vice versa with a minimum of effort, crawling up and down the thread instead of having to swim.
What is perhaps more remarkable, is that, when the snail wishes to move to another part of the pond, it eats the thread inch by inch, digests it and uses the material again to construct another thread in the new quarters. In this case, the thread is so fine that it cannot be detected when the animal is in its natural haunts. Only in an aquarium, and under special illumination can it be seen.