Nervous System
Worms have no eyes or ears but, in compensation, an extremely sensitive nervous system. So sensitive that they are able to notice a bird walking above them or sunlight on their tender skins. Either of these sensations will send them diving for cover, very quickly. They are also able to learn very simple tasks.
Contained in their anterior — the portion in front of the clitellum — are two nerve endings, called photoreceptors, which are extremely sensitive to light. There are also thousands of tense-like nerve endings concentrated over the length of the body. These are particularly sensitive to ultraviolet light, exposure to which will kill worms and constitute the warning system which quickly sends them burrowing for cover.
Digestion
Like birds, worms have a gizzard where the food is ground to a fine consistency. It is then acted upon by a secretion of calcium carbonate, (This is one reason, worms help to neutr³alise acid soils.) The food is next passed on to the actual digestive tract for further processing by means of a variety of enzymes, excreted both by the worms and importantly, by bacteria, (The enzymes are also thought to influence the pH of the soil.)
During the digestive process, a proportion of insoluble minerals are converted to a plant-available soluble form, carbon is released to the atmosphere as carbon dioxide, and cellulose is partially broken down.
Diet
The eating habits of worms are very varied. Some are strictly herbivores, most are omnivores and one or two species of African arms are carnivores. Some prefer a nutrient-rich diet, others eluding most of the Australian indigenous worms do not The general rule is that worms will eat anything that once was living, t not while it is alive.
In very compact soil, swallowing soil is the earthworm’s main of moving about and they ingest about 50 per cent of what encounter. It is generally believed that earthworms eat their n weight every day, although some researchers claim the daily take to be less than this, perhaps only half.
Even if their daily rate of eating is only half their individual y weight, it is still a substantial amount and a characteristic hich is most beneficial to us. When you consider that worms have to extract their nutrition from the soil, this high food intake is understandable. To get the little they need for sustenance, they have to ingest a relatively huge amount.
Earthworms ingest food by pushing the inside of their mouth forward and inside out. It closes over the chosen morsel which is then pulled back in and passed on into their digestive tract. (They have no teeth and so need their food is to be partially degraded or pre-processed as, for example, in manures.)
A Hollow Tube
All worms are essentially a hollow tube, the hollow being the digestive tract. This is surrounded by muscle like a section of bicycle tube which runs the length of the body. The muscle is in mm enclosed by a series of muscles which ring the body and can be seen as segments. These segmental muscles are filled with water. The skin forms the outer sheath. It is the presence of the liquid — liquids being incompressible — that provides the real key to the worms’ locomotion.
Hydraulics
Worms are a combination of hydraulic ram and jack. They are able to exert great force with their muscles, which are made effective by the presence of the water enclosed within the segmental muscles. Their movement is achieved through coordinated contraction and expansion of their muscle groups, in a very smooth and fluid action.
Other muscles which control the setae cause these body hairs to protrude as an additional grip, and these are protruded and withdrawn in coordination with the segmental and bicycle tube’ muscle. A worm, given time, can push its way through a hole less than one-quarter of its own relaxed diameter, or can quite firmly fill one twice its sire. Worms can grip so tightly that, if you try to pull one out of a hole, you may well pull it in two before it yields.
Tunneling
In forward motion, the segments of the front section of the worm are expanded so that force is exerted on the surrounding soil, setae protruding, while simultaneously the segments behind the expanded portion are progressively contracted in a ripple or peristaltic action, setae withdrawn. This jams the forward section in place and the rest of the worm can be drawn forward by contraction of the ‘bicycle tube’ muscle. This process is then reversed. The rear segments expand (setae protruding0 the front contacts (setae withdrawn and is pushed forward by elongation of the “bicycle tube” and the rear drawn up. In endless repetition of this co-ordinated movement, involving no stop-start but continuous fluidity, the worms can move through remarkably hard soils. They are able to move forward and backward with equal ease. Darwin considered earthworms, weight for weight, the strongest animals in the world.
Sometimes, worms will follow the channels left by decayed roots ( perhaps eating the root), or if the soil is soft enough just push their way through.
Worms are also great mining engineers, because their tunnels are coated with mucus which, on hardening as it dries, shores up the roof and walls. The mucus forms yet another of the worm’s gifts to the soil
