The family Talpidae includes the moles, shrew moles, and desmans, all of which are confined to the north of North America and Eurasia. These predominantly burrowing insectivores (29 species in 12 genera) are highly secretive and because of their way of life have, in general, been poorly studied. The species that has, to date, received most attention from naturalists and biologists alike is the European mole (Talpa europaea), whose way of life and behavior are probably quite similar to many of the other species within this family.
Moles are highly specialized for a subterranean, fossorial way of life. Their broad, spade-like forelimbs, which have developed as powerful digging organs, are attached to muscular shoulders and a deep chestbone. The skin on the chest is thicker than elsewhere on the body as this region supports the bulk of the mole’s weight when it digs or sleeps. Behind the enormous shoulders the body is almost cylindrical, tapering slightly to narrow hips with short sturdy hindlimbs (which are not especially adapted for digging), and a short club shaped tail, which is usually carried erect.
In most species, both pairs of limbs have an extra bone that increases the surface area of the paws, for extra support in the hindlimbs, and for moving earth with the forelimbs. The elongated head tapers to a hairless, fleshy pink snout that is highly sensory. In the North American star-nosed mole (Condylura cristata), this organ bears 22 tentacles each of which bears thousands of sensory organs.
How Do Moles Dig Burrows?
The function of a mole’s burrow is often misunderstood. Moles do not dig constantly or specifically for food. Instead the tunnel system, which is the permanent habitation of the resident animal, acts as a food trap constantly collecting invertebrate prey such as earthworms and insect larvae. As they move through the soil column invertebrates fall into the animal’s burrow and often do not escape before being detected by the vigilant, patrolling resident mole.
Once prey is detected, it is rapidly seized and, in the case of an earthworm, decapitated. The worm is then pulled forward through the claws on the forefeet, thereby squeezing out any grit and sand from the worm’s body that would otherwise cause severe tooth wear-one of the common causes of death in moles.
If a mole detects a sudden abundance of prey, it will attempt to capture as many animals as possible, storing these in a centralized cache, which will usually be well defended. This cache, often located close to the mole’s single nest, is packed into the soil so that the earthworms remain alive but generally inactive for several months Thus, if an animal experiences a period of food shortage it can easily raid this larder instead of using essential body reserves to search for scarce prey. In selecting such prey for the store, moles appear to be highly selective, generally choosing only the largest prey available.
How Do Moles Construct Tunnels?
Tunnel construction and maintenance occupy much of a mole’s active time. A mole digs actively, throughout the year, although once it has established its burrow system, there may be little evidence above ground of the mole’s presence. Moles construct a complex system of burrows, which are usually multi-tiered. When a mole begins to excavate a tunnel system. It usually makes an initial relatively straight exploratory tunnel for up to 20 meters (22 yards) before adding any side branches. This is presumably an attempt to locate neighboring animals, while at the same time forming a food trap for later use. The tunnels are later lengthened and many more are formed beneath these preliminary burrows. This tiered- tunnel system can result in the burrows of one animal overlying those of its neighbors without them actually being joined together In an established population, however, many tunnels between neighboring animals are connected.
Mole’s Sense of Navigation
Moles have a keen sense of orientation and often construct their tunnels in exactly the same place every year.
In permanent pastures, existing tunnels may be used by many generation of moles. Some animals may be evicted from their own tunnels by the invasion of a stronger animal and, on such occasions, the loser will have to go away and establish a new tunnel system.
These master engineers are highly familiar with each part of their own territory and are suspicious of any changes to a tunnel, which makes them difficult to capture. If, for example, the normal route to the nest or feeding area is blocked off, a mole will dig either around or under the obstacle, rejoining the original tunnel with minimum digging.
Our knowledge of the sensory world of moles is very limited. They are among the exclusively fossorial species, the eyes are small and concealed by dense fur or, as in the blind mole Talpa caeca, covered by skin Shrew moles, however, forage not only in tunnels beneath the ground but also above ground among leal litter Although they may have a keener sense of vision than other species they are still probably only able to perceive shadows rather than rely heavily on vision for detecting prey or for purposes of orientation.
The apparent absence of ears on almost all species is due to the lack of external ear flaps and the covering of thick fur over the ear opening. It has, however, been suggested thar ultrasonics may be an important means of communication among fossorial and nocturnal species. But of all the sensory means olfaction appears to be the most important medium-a fact supported by the elaborate nasal region of many species, together with the battalion of sensory organs stored within this area.
The brief breeding season is a frantic period for moles, as females are receptive for only 24 to 48 hours. During this time males usually abandon their normal pattern of behavior and activity, spending large amounts of time and energy in locating potential mates. Mating takes place within the female’s burrow system and this is the one period of non-aggressiveness between the sexes.
The young, with an average of three to the litter, are born in the nest four weeks later. Weighing less than 4 grams (ounce), the pink, naked infants cannot control their body temperature and rely on their mother for warmth The young are fed entirely on milk for the first month, during which they rapidly gain weight. Juveniles remain in the not until they are about five weeks old at which time they begin to malor short exploratory foray in the immediate vicinity of the nest chamber. Shortly thereafter they into accompany their mother on more exterite explorations of the burrow system and may disperse from there of their own accord, those that do not leave will soon be evicted by the mother.
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