Insectivora

The insectivores are small mammals that live on or in the ground. They are considered to be the most primitive order of mammals and their anatomy shows very little difference as they have progressed though the evolution compared to other mammal orders. They have a relatively small brain size but comparatively large size of their lobes serving the sense of smell and plant grade feet, usually with five toes.

The order in Britain is represented by the hedgehog, four species of shrew and the mole, and of these only the hedgehog and one species of shrew are found all over the British Isles.

The diet of insectivores consists for the greater part, of invertebrates. This diet makes then totally innocuous to man, unlike rodents who tend to be very destructive. Infact not only do insectivores not harm man but may be positively beneficial in the reduction of harmful insects and there larvae. The hedgehog is more omnivorous than moles or shrews and will include some small amount of vegetable matter in its food.

They are not confined to a diet of small insects although it is a large part of their diet, and will attack any animal that they are large enough to overpower and fast enough to catch. Both moles and shrews are considerably voracious and will consume more than there own body weight in a 24 hour period and is starved of food will usually die within a 12 hour period. Their whole life is an incessant hunt for food interspersed with short periods of sleep. This incessant need of food is the requirement imposed by having a very high metabolism. In fact the average consumption of oxygen per gram of body weight every hour is five times greater then that of mice and voles. The expenditure of this much energy is directed towards maintaining their body heat as the 12 hour period can be extended slightly by providing warm bedding to maintain the body heat for longer. There may be link between the high body temperature or high metabolism and the preponderance of protein compared with small amounts of fat and carbohydrates in the diet.

Both shrews and moles are extremely aggressive and quarrelsome and when ever two individuals of the same species meet (except male and female during the breeding season) one will invariably attack the other.

The activity of moles and shrews differs strongly with that of the hedgehog, which is the largest insectivore in the Isles, which makes it a much more sluggish creature, having a much higher volume to surface area ratio and specializes in long periods without food during hibernation.

The differences mentioned above between the mole, shrews and hedgehog are reflected in the anatomy of the animals and thus in the classification by systematists. 2 of the eight superfamilies of insectivores are found in Britain and Ireland and their grouping emphasises that the moles and shrews are more closely related to each other then they are to hedgehogs.

Superfamily Erinacoidea

Family; Erinacidea;- Hedgehog (Erinaceus europaeus)

Superfamily Soricoidea

Family; Soricidae;- Common shrew (Sorex araneus), Pigmy shrew (Sorex minutus)

Family; Talpidae;- Mole (Talpa europaea)

The first and the last of these families in Britain each contains a single species, where as in Ireland there are no moles, There are four species and one sub-species of soricidae in Britain but only the pigmy shrew reached Ireland before the Irish sea flooded. These four species belong to three genera; Sorex (Red-toothed shrews) Neomys (Water shrews) and Crocidura (White toothed shrews).

Most of the insectivores are rather noisy animals. Shrews squeak and chatter as they rummage and scurry about the undergrowth but some of their notes are so high as to be nearly inaudible to many people. Less often heard is the very similar but more powerful squeak of the mole, which will squeak loudly if captured. The hedgehog when rooting about at dusk, makes a lot of grunting and snuffling noises that are quite unmistakable. When it stands still it also makes a ticking or clicking sound that perhaps may be produced not with the voice but with the teeth. This sound is not heard when the animal is on the move. In addition the hedgehog sometimes makes a loud screaming noise when it is pounced on by a predator before it has had time to curl up.

Although much of the knowledge of the biology of insectivores is fragmentary, the general outlines of the breeding cycle are known. The shrews, whose normal life span extends to just over a year, can experience only one breeding season. The mole and the hedgehog which tend to live longer probably go through more than one. In all of these mammals the breeding cycle is marked by physiological and anatomical changes. Out of season the whole of the reproductive organs are very small, but as the breeding cycle encroaches, these organs increase dramatically in size, in both sexes, then afterwards decrease in size again back to their former condition.

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