Monday, November 03, 2008

Urban Wildlife Watch: Moles and Shrews

Most people mistakenly mistake these little creatures for rodents – mice and rats – but they are completely different beasts; they are called Insectivores. Insectivores do look very much like mice - small, furry, with tails, but there are some VERY big distinctions.

1. Diet – Moles and Shrews eat insects, hence the name Insectivores. They eat the whole range from juicy grubs, worms, and larvae of flying insects to grasshoppers, moths or whatever they can get their hands on – including crayfish.

2. Very quick metabolism. For the most part, small animals have faster metabolisms than larger animals. But moles and especially shrews are metabolic sprinters. Their hearts beat so fast - 800 heart beats a minute! - and they absolutely must consume lots of energy per day or they will die. No kidding. A typical shrew, weighing 15 grams must consume its equivalent body weigh per day or risk starving to death.

3. Voracious hunters. That explains why these little guys are mean, hunters. They don’t fool around. The joke in field biology is that if you set out a trap to catch small mammals and you catch 2 shrews, you’ll only find one shrew in the trap. That’s because if they have to, they will eat each other or another kind of animal beside insects…They crave protein.

4. Teeth – moles and shrews have a mean set of teeth. That’s because of their diet. They need sharp rows of teeth to make quick work of living, moving and sometimes fighting meals. They tend to bare their teeth, that look like a row of Vs all connected VVVVV. They almost seem to snarl.

5. Some body shape or morphological differences. There is always variation in body shape among species, but moles and shrews have different shaped heads than a typical house mouse or field mouse. Moles tend to be fat stocky creatures with small round heads. They don’t tend to have elongated noses or rostrums like a mouse. And they completely lack fleshy ears and have little pin-hole eyes. Moles really are blind. And they have HUGE hands. They use them for digging through the soil underground. Compared to moles, shrews do look more like mice, but their noses are very long and pointy, more so than a mouse’s nose; but they also have the tiny pin-hole eyes.

But I must be honest with you, you not likely to actually encounter a mole or a shrew. Like their Rodent cousins they are small and do live underground. They make or take over burrows. Moles are especially adept at digging tunnels and burrows and more than the shrew, they prefer to stay underground as much as possible. And those big hands that moles have testify to their underground lifestyle, fancy word -- fossorial. Insectivores are very fast. When they run they seem to shoot like a lightening rod – that’s thanks in part to that super fast metabolism.

When I was trapping for field mice, I often caught shrews - Short-tailed shrews and Blarina brevicauda – the only venomous mammal in the world.
Southern Short-tailed shrew. Image credit: New World Encyclopedia
Blarina brevicauda image credit: Animal Diversity Web
And believe it or not, mole fur is some of the plushest and softest fur I have ever touched. It reminds me of a stuffed animal or chenille yarn. Cozy.

Mole: image credit: Palaeos

Ken Catania, of Vanderbilt University, studies moles and their feeding behavior. I attended his presentation at the ISBE Conference and I was mesmerized. It was the best science talk, ever. These guys are so fast Dr. Catania has to doctor-up his high speed cameras to catch these guys in action. A mole or a shrew can attack and consume a prey (earthworms) in less than a fraction of a second. Ooh, I have to share the earthworm stuff, too, but later.


Miriam Goldstein said...

Between the bats and now the shrews and moles, I am undone with cuteness! None of my marine invertebrates have soft fuzzy fur and GIANT HANDS.

DNLee said...

hahaha. what the giant squid? those tentacles and those suckers are impressive.

Unknown said...

I had no idea there was a venomous mammal! And I had no idea that the moles were soft. Interesting.

Anonymous said...

It is not only shrews that are venemous. The slow lorises of Se Asia (a primate no less) also have a poisonous bite, which has caused human beings to be hospitalised or even killed. The toxin is secreted by the brachial glands and activated by an enzyme in the lorises saliva. In humans it triggers a violent allergic response in susceptible people.

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