Critter Corner No. 15

Critter Corner No. 15
the Eastern Mole
by
George Sly

Most of the mammals which make Goose Pond FWA their home are secretive and seldom seen. The subject of this edition of Critter Corner is no exception. In fact, the Eastern Mole is made even more elusive by the nature of its fossorial (burrowing) behavior. Certainly we see the mounded earth and raised tunnels of this mammal but the maker of these telltale trails is itself seldom seen.

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 I must admit that I am intrigued by moles. Their subterranean existence, so strange and difficult for us creatures of the light to imagine, fascinates me. What must it be like to spend life in nearly perpetual darkness? How do they find food? How is it possible to burrow through solid ground? Why does their fur always seem so clean? What do they do in the winter when the ground is frozen? Yes, moles stimulate a lot of questions for me.

 Moles are found throughout much of the world and their clan consists of around 40 species. Here in the eastern United States we have three species but only the Eastern Mole is found at Goose Pond FWA. The Star-nosed Mole lives in NE Indiana while the Hairy-tailed Mole exists in eastern Ohio and Kentucky and on up into New England. Moles are closely related to shrews. That “baby mole” your cat brings to the doorstep, and then abandons, is likely not a mole but a Short-tailed Shrew.

 Our Eastern Mole bears the scientific moniker of Scalopus aquaticus. The genus name is derived from the Greek words for digging and foot and refers to the mole’s enormous forefeet. The specific name is apparently a bit of a misnomer. Various sources report that the specimen that Carolus Linnaeus (the “father of modern taxonomy”) used in naming the species was found dead in water. Although moles can swim they are not aquatic.  
 Of course any animal that has a highly specific lifestyle such as that of the Eastern Mole will likely have major adaptations for that mode of existence. Notable among these, as illustrated in the image below, are the somewhat flattened, wedge-shaped skull and the powerfully enlarged bones of the forelimbs. The muscles that power the front legs are tremendously developed. They give the animal the appearance of having heavily trained for some body-building competition; think Arnold Schwarzenegger in his prime. The relatively smaller hind legs are used for bracing during digging and to shuttle loose soil rearward and have less need for powerful development.

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The tail is somewhat long with external hairs which give it tactile ability useful when backing up in a tunnel. The silky body fur is adapted for shedding soil thus keeping the coat relatively clean.

 Moles do have eyes but they are reduced in size and the eyelids are fused shut over them. Thus they are barely functional and serve to detect light and darkness. Unlike most mammals moles have no external ears (pinnae). These would not be a good idea when burrowing through narrow tunnels and loose soil. They can hear and are also quite sensitive to vibrations in the ground. The sense of smell is well-developed and their nose is also exquisitely sensitive to touch. In fact, research has shown that moles have highly specialized nerve tissues forming what are called Eimer’s organs in the epithelium of their nose. These reach their highest degree of development in species such as the Star-nosed Mole shown here.
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In the Eastern Mole these organs are less developed and are covered by thicker epidermis. This is thought to be because of the differences in burrowing substrate of the two species; the Star-nosed being more often found in wetter, softer soil.

 The Eastern Mole is often blamed for damaging garden plants but is in fact more often a voracious predator. Its primary prey is earthworms. These creatures are sensitive to the movements of moles and I have actually seen them flee above ground and rapidly (for an earthworm) crawl away from a burrowing mole. I once ran across an interesting paper in an online journal in which author Kenneth Catania described how folks in the southern United States practice “worm grunting”. By vibrating a wooden stake driven into the ground they are able to force worms to the surface where they are collected for fishing bait. Catania concludes that the vibrating stake mimics the pulsations caused by burrowing moles thereby eliciting the earthworm’s escape behavior. Interestingly he also notes previous studies that suggest Wood Turtles and Herring Gulls “vibrate the ground to elicit earthworm escapes.”

 Other animals eaten by moles include scarab beetle grubs (including Japanese beetles), ground beetles, slugs, and centipedes. Some vegetation may be eaten particularly grass seeds.

 Eastern Moles can burrow 10 to 15 feet per hour and their surface runs are made as they search for food. Deeper burrows (10-18 in.) and chambers are used for rearing young and resting. In the winter, burrows are made below the frost line.

 Animals which have relative few predators often have lower rates of reproduction. Eastern Moles are an example and typically have one litter per year. The babies are born in the spring and usually number three to five. At least one study has indicated that moles may live more than five years. While predation is limited due to their burrowing habit, they do have their enemies. Among these are domestic dogs and cats. Owls also take moles and it is thought that they do so on those rare occasions when the former come to the surface.

Of course, when moles invade lawns, humans become a major threat to them as well. Their tunneling certainly complicates mowing the yard. Their underground burrows may also be used by voles which may then attack the root system of garden plants. The other side of this coin is the mole’s ability to destroy insect pests, slugs, and snails. In addition, their burrowing activity tills and aerates the soil and allows water penetration into deeper soil layers. In light of this, perhaps a little more tolerance for this highly interesting mammal is called for. Rolling their surface runs before mowing pretty much eliminates the issue of “skinned” lawns. It is certainly less expensive than buying traps or calling an exterminator and definitely more environmentally friendly that sowing poisonous baits. All it takes is a little more time and patience on our part coupled with a dose of willingness to share the earth with another of natural selection’s decidedly fascinating creations.  

Reference:
Catania, Kenneth C. 2008. Worm Grunting, Fiddling, and Charming—Humans Unknowingly Mimic a Predator to Harvest Bait.  PLoS ONE. 2008; 3(10): e3472.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2566961/