Retracts and turns

Edward Stuart Russell, The behaviour of animals : an introduction to its study, Londres. Edward Arnold, 1938, p.2-4.

My third example illustrative od directive activity relates to a familiar insect larva, the caddis worm, in this case of the genus Limnophilus, which lives in a tube constructed of little piece of leaf and stalk of aquatic plants. Ejected from its tube it wanders vaguely round until it touches the empty tube, then fasten on to it and crawls all over it till it finds the front entrance and goes in head first. The hind entrance is too narrow to permit of its entry. When it is inside it enlarges the narrower hind entrance until it gets its head and legs free, but then retracts and turns right round Inside the tube so that its head and legs emerge at the front end ; then all is well and it carries on with the main business of its life, which is eating.
If however the empty tube is not avaible the caddis larva will, after wandering around for some time , construct a new one out of any suitable material it finds, building first a collar or zone rounds its thorax and pushing this further back as it adds bits on the anterior edge.
The important thing to note is that if the first effort to cover it’s nakefness fails, that is, if it cannot find the old tube, it adopts a totally different line of action and constructs a new tube.
Let us take now some cases of persistent striving where the immediate object is not so obvious…/….

…/….. So too the caddis larva’s activity is satified and ceases only when, by one method or the other it manage to clothe its nakedness in a suitable tube.