Featured Creature: Star-nosed Mole

Photo from The Daily Mail

What sort of voracious creature cannot see or smell well, feels its way around, and looks like someone’s nightmare enlarged?

The star-nosed mole, of course, or condylura cristata!

Photo from The Daily Mail

So what is a star-nosed mole and what is that horrible thing on its nose?

The star-nosed mole is a very distinctive mammal, covered in dark brown, water-repellent fur, and wide forefeet tipped with talons that are designed for digging. The palms of their pinkish and black feet face outwards. Their feet also make excellent rudders, steering their bodies as they swim through water. Their tail is long and hairy, and in winter it swells up with fat, making it 4 times larger than its normal size, so as to serve as a fat storage organ to help the mole survive the winter months. 

The star-nosed mole is sometimes called an optimal forager. This means it has evolved the ability to identify and consume food very efficiently in order to survive in a highly competitive environment.

In almost all its characteristics besides the tentacles, the star-nosed mole actually looks like a typical member of the mole family. It has a big, stout body, a sinewy tail, and massive forelimbs that are highly adapted for digging. The short but dense coat of fur is black and dark brown on the back and fades to lighter brown on the underside. Measuring about the same size as a rat, this species stretches an average of 6 to 8 inches and weighs only 1 or 2 ounces. Besides the presence of sex organs, males and females are very similar in appearance. 

About that Nose

Its star-shaped nose is by far the most conspicuous characteristic of this species. The snout for which they are named has 11 pairs of little pink tentacles on its tip, splayed out like a star. This touch organ has more than 25,000 minute sensory receptors that the mole uses to feel its way around. It can even detect seismic wave vibrations from often distant earthquakes! 

This snout is an extremely sensitive structure covered with touch receptors known as Eimer’s organs. The nose is about 1 cm in diameter and has roughly 25,000 Eimer’s organs distributed on 22 fleshy finger-like appendages that ring its nostrils. These tendrils are in constant motion as the mole explores its environment. 

Photo from National Wildlife Foundation
Photo by Kenneth Catania

The star-nosed mole is functionally blind (they are colorblind and only poorly see light and movement), so this strange-looking snout was long suspected to be used to detect electrical activity in prey animals, though there has not been much empirical support found for this hypothesis. It is believed that the sensory receptors on the nose have three distinct purposes: they can sense the microscopic textures of objects, the electrical fields of surrounding objects, and even ground vibrations in the soil. 

It hasn’t been definitively proven that the mole can sense electrical fields, but this ability is strongly inferred from the results of studies in which the mole is drawn to batteries or other strong electrical fields in the water. 

Its sensitive nasal structure is divided into a high resolution region and less sensitive peripheral areas. In this way, the star effectively works as a “tactile eye” where the peripheral rays (1–10 on each side) study the surroundings with erratic movements and direct the 11th ray to objects of interest that it might want to eat, while foraging in dark confines. And based on its concentration of neurons, its sensitivity is about six times that of the human hand!

A fast food lover

The nasal star and teeth of this species appear to be primarily adapted to feed on extremely small prey. The star-nosed mole is also reputed to be a very fast eater, much like the enthusiastic guest who wants second helpings before everyone else is served! A report in Nature awards this beast the title of fastest-eating mammal, taking as little time as 120 milliseconds to identify and consume individual food items. 

Its brain decides in approximately 8 milliseconds if a prey is edible or not, which pace is at the very limit of the speed of neurons! So this mole is a real pig. Just for comparison’s sake, a similar process would take 600 milliseconds for a human reaction.

With extremely short handling times for eating very small prey, star-nosed moles can profitably consume foods that are not worth the time or effort of slower animals, and having a special food category available just to themselves is a big advantage. Furthermore, just behind the 11th ray of the star, the star-nosed mole has modified front teeth that form the equivalent of a pair of tweezers. High-speed video shows these specialized teeth are used to pluck tiny prey from the ground as a means of consuming them. So this creature is highly adapted to the sort of environment that it inhabits.

According to studies, more than half of its brain is dedicated to processing sensory information from its nose, even when the nose itself is only 10% of the mole’s total size. In a sense, the nose serves as a substitute for eyes, with all of its sensory information producing a tactile map of the mole’s immediate environment. 

Photo from Catania Lab, Vanderbilt University

Star-nosed moles are also able to smell underwater! Though this was previously thought impossible in mammals, they accomplish this feat by exhaling air bubbles onto objects or scent trails and then inhaling the bubbles to carry scents back through the nose. Such a diversely talented creature, huh? 

Check out the mole’s claws, handy for digging muddy burrows in wet dirt. They use them to dig shallow tunnels up to 100 feet in length and forage through marshes and swamps. These excellent diggers with their broad feet and sharp claws are ideal for moving dirt and for burrowing their nests underground. They generally build these nests in deeper tunnels away from predators, usually below a protective structure, like rocks or logs. They use sticks, leaves and dry grass to line their nests and keep them dry.

Where do these creatures dwell?

The star-nosed mole is generally found in swampy areas in the northeastern part of North America. They like wet lowland areas in which they can dig their burrows to hide from predators. These animals prefer areas with poor drainage, such as coniferous and deciduous forests, wet meadows, clearings, marshes and peatlands. They will also inhabit stream banks, lakes and ponds, and will venture into them for food. They forage on small invertebrates such as aquatic insects, worms, and mollusks, as well as small amphibians and small fish. The home range of an individual star-nosed mole is thought to be less than 4000 square meters.

Range of the Star-nosed Mole (from WikiCommons)

Star-nosed moles have  also been found in dry meadows farther away from water, such as in the Great Smoky Mountains as high as 1,676 meters. So I guess they are mountain climbers as well! However, the star-nosed mole much prefers wet or poorly drained areas and marshes. 

There are 39 species of mole, and the star-nosed mole is the only species that lives in swamps and marshes. Star-nosed moles are diurnal (i.e. they are active both day and night), and they remain active throughout the winter when they can be seen tunneling through the snow and swimming in ice-covered streams. Brrr! But this animal is skilled at thermoregulation, so can maintain a high body temperature in a wide range of external conditions, which explains why it can thrive in cold aquatic conditions.

Photo from Tumblr

Who are their main predators? What are their prey species?

The star-nosed mole faces the constant threat of natural predators in the wild. This species is not usually disturbed or harassed by humans, because its habitat does not generally overlap with where people live. They have many other dangers to be wary of, though. They must watch out for red-tailed hawks, great horned, barn and screech owls, foxes, weasels, minks, skunks, domestic cats and even large fish such as the northern pike or largemouth bass, which will swallow them up in one gulp. Yummy!

The star-nosed mole spends most of its own day foraging and eating. About half of its diet consists of worms; the other half consists of mollusks, small fish, damselflies, dragonflies, and other insects. It prefers to hunt in underground burrows or in the water and only rarely comes up to the ground level for food, which is why we don’t see them very often despite their ubiquity.

This creature is a good swimmer that can forage along the bottoms of streams and ponds. They can dive for several seconds, sometimes remaining underwater for as much as half a minute. They also will often dig shallow surface tunnels that they use for foraging with underwater exits. During the wintertime, star-nosed moles hunt more in water because the wet ground is likely frozen, and they will even swim under ice. 

If they come above ground searching for food it is usually at night. Although normal progression on the surface of the ground or snow is slow, an alarmed star-nosed mole can run short distances at speeds of 4-5 miles per hour in ‘panic mode’. Although this species is active by day as well as by night, it spends about half of each 24 hour period resting or sleeping curled upright with the head bent under the forelimbs, which is a lot better than most of us manage (except sometimes in mid-afternoons at our desks)!

Why are they of interest to researchers?

These star-nosed moles are a treasure for research, because the sensitive feelers on their nose offer us a means to understand more general principles about how human brains process and represent sensory information. This highly-acute organ operates much like vision in its speed and responsiveness, which has led to recognition of this species in the Guinness Book of World Records as the world’s fastest forager, so you might think twice before inviting this rude guest to dinner. It might just scarf down everyone’s food in the blink of an eye!

This creature’s foraging activity has been of great interest to scientific researchers. They have found that when the outer appendages of the star-shaped nose come into slight contact with a potential food source, the nose is quickly shifted so that one or more touches are made with the fovea (the two lower appendages on the 11th pair) to explore objects of interest in much greater detail – especially when it is potential prey.

This foraging behavior is exceptionally fast, such that the mole may touch between 10 and 15 separate areas in its environment every second, which is really ‘covering the ground’! Evidently, there are molecules in the mole’s star-shaped nose that help turn a physical force into the electrical signals that are the currency of the nervous system. Because of this sensitivity, this fascinating creature can locate and consume 8 separate prey items in less than 2 seconds and begin searching again for more prey in as little as 120 milliseconds, although the average time is 227 milliseconds. So it can quickly gobble up everything it comes across!

Photo from Anamalia.bio

The star-nosed mole may also be a model organism for research into how brains process touch. A better understanding of its sensory apparatus may lead in future to the development of new types of neural prostheses. In addition, the speed and precision of the mole’s processing may provide insights into designing intelligent machines to mimic their remarkable sensory ability. 

What other ecological impacts do they have?

The star-nosed mole benefits other living things, including humans, by preying on the larvae of pest insects and aerating soil, keeping plants healthy. They are listed by the IUCN as of “least concern” so they are not currently threatened. However, due to potential land development and other possible risks, the growth of human population can lead to a destructive filling in of the wetlands upon which their survival depends. They may also occasionally extend their tunnels into lawns adjacent to wetlands, damaging the sod, so one might say that they are not ‘out of the woods’ but neither are they ‘in over their heads’ as yet! 

By Fred Jennings