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Facts About Creeping Voles and Their Strange Chromosomes

Linda Crampton is a writer and experienced science teacher with an honors degree in biology. She enjoys writing about science and nature.

Microtus lusitanicus belongs to the same genus as the creeping vole and is a close relative.

Microtus lusitanicus belongs to the same genus as the creeping vole and is a close relative.

An Intriguing Animal

The creeping vole (Microtus oregoni) is an interesting and unusual animal. Its sex chromosomes are strange in comparison to those of most other mammals. Female humans have two X chromosomes. Males have one X and one Y chromosome. This is also the case for nearly all of our mammal relatives. Creeping voles have a different system, however. Females have an unpaired X chromosome. The male has two X chromosomes, but only one is active. In both females and males, the chromosomes contain tiny sections of the Y chromosome that was present in the distant ancestors of the voles.

Voles are also known as field mice and meadow mice, though they aren’t actually mice. They are rodents, however. They belong to the family Cricetidae in the rodent order, which also contains lemmings, hamsters, and the new world rats and true mice.

The creeping vole lives In the Pacific Northwest region of North America. The region encompasses British Columbia, Washington, and Oregon. Some people include southern Alaska, the Yukon, parts of Montana and Idaho, and northern California in the definition of “Pacific Northwest.” Despite their strange chromosomes, both the male and the female versions of the creeping vole have suitable reproductive organs for their gender.

The video above shows creeping voles at the PAWS (Progressive Animal Welfare Society) in Washington. They appear to be a rescued group of young voles. At one point in the video, one of the animals accepts food delivered by a staff member.

Facts About Voles in the Genus Microtus

Voles and humans belong to the class Mammalia. We belong to the order Primates in the class Mammalia. Voles belong to the order Rodentia. Multiple genera of voles exist. The information below applies to members of the genus Microtus that live in North America, including the creeping vole.

Physical Features

Voles look somewhat like mice. They have a stouter body, however. They also have a shorter tail than mice. Their tail is lightly haired. Their eyes are small and their ears are partially hidden by fur. The genus name “Microtus” is derived from Latin and means “small ears.” Voles have short legs. The adults are often said to reach a length of between five and eight inches, including the tail.

Tunnels and Burrows

The voles travel along runways above ground and through shallow tunnels underground. Their burrows are also underground. The runways and the multiple tunnel entrances are usually hidden by vegetation. The animals are active during the day and during the night. The voles or their droppings may be seen at any time of year. They don’t hibernate, even in areas where there is snow on the ground in winter.

Herbivorous Diet

The animals are herbivores. They eat a variety of plants and plant parts, including grass, other types of plants, roots, bulbs, and tubers. They also eat tree bark. North American voles in the genus Microtus generally don’t climb trees, but this isn’t an impossible act for them. They may be able to climb onto low branches.

Their choice of food sometimes brings voles into conflict with humans. Unfortunately, in certain areas, some vole species are considered to be pests.

Additional Facts About the Creeping Vole

In addition to the general facts mentioned above, researchers have discovered some specific information about the creeping vole.

Distribution and Habitat

The northern limit of the creeping vole’s distribution is southwestern British Columbia, its southern one is northwestern California, and its eastern one is located in Washington. The species lives in forests, woodlands, and areas with long grass. It’s said to be more common in clearcut areas than dense forests and in drier rather than moist ones.

Features and Activity

The animal is dark brown, dark grey, or black. It’s generally the smallest vole in its area. Adults are usually just over over six inches long. Like other members of its genus, the creeping vole may be active at any time of the day or night, but it’s most active during the night.


The female has multiple litters in a year. She may produce as many as four or five litters during the spring, summer, and fall, though the usual number is probably smaller. Gestation lasts for around twenty-three days. The litters consist of around three or four youngsters. The offspring are born in a sheltered area, such as a burrow or a cavity under a log. The female builds a nest of vegetation for them.


The species has a short lifespan. Its maximum age appears to be around fifteen months. More facts about the animal’s life in the wild need to be discovered. The animal may have a much shorter life than expected due to predation. This fact also applies to some other vole species.

Human and vole cells vary in shape. Their basic components are shown in the illustration below. The illustration is a good guide to cell structure, but it’s an approximation. Cells have thousands of mitochondria, for example. (The singular form of mitochondria is mitochondrion.) The chromosomes are located in the nucleus of a cell.

The Nature of Mammalian Chromosomes

A mammalian chromosome consists of DNA (deoxyribonucleic acid) and a small amount of protein attached to the DNA. The DNA contains instructions for making the many types of protein that the body needs for its structure and function. The instructions are encoded in a series of chemicals known as nitrogenous bases. The order of these bases in a molecule of DNA can be likened to the order of letters in words. In both cases, meaning is created. Unlike the case in our alphabet, there are only four “letters” in the DNA one: A (for a chemical called adenine), T (thymine), C (cytosine), and G (guanine).

A DNA molecule contains two strands of nitrogenous bases that are joined together. Adenine on one strand bonds to thymine on the other, while cytosine on one strand binds to guanine on the other. The ladder-like structure that results is coiled into a spiral shape known as a double helix. A flattened section of this helix is shown in the illustration below.

The chromosomes are located in the nucleus of a cell. When the cell is making a protein, only one strand of the DNA is “read.” The code is copied onto a molecule called messenger RNA (or mRNA). This molecule then leaves the nucleus and travels to a ribosome, where the correct protein is made. A section of DNA that codes for a particular protein is called a gene.

The Sex Chromosomes: X and Y

Humans have 23 pairs of chromosomes, or 46 individual ones. The chromosomes in one of the pairs are referred to as the sex chromosomes because they determine our gender. Females have two X chromosomes and are designated XX. One of the chromosomes was present in the father’s sperm cell and the other in the mother’s egg cell. Males have an X chromosome inherited from their mother and a Y chromosome obtained from their father and are said to be XY. This pattern is the same in nearly all mammals. The creeping vole is an exception, however

The human Y chromosome is shorter than the X one. A human X chromosome is about 156 million base pairs long. The human Y chromosome is about 59 million base pairs in length. It’s believed to be gradually disappearing. Though that may sound horrifying to some people, it may be comforting to know that the process will probably take several million years. It’s interesting that the creeping vole does very well without a Y chromosome.

DNA is replicated and distributed when a cell divides. This enables each of the resulting cells to have the required genetic information.

Structural features of a chromosome

Structural features of a chromosome

Strange Sex Chromosomes in Creeping Voles

Despite the loss of the Y chromosome in the creeping vole, both male and female voles are born. It’s unknown how the Y chromosome was lost. The scientists investigating the situation have an idea, however. They suspect that the original chromosome that was present in the ancestors of the creeping vole broke during meiosis. Meiosis is the process in which a cell produces egg and sperm cells that each have half the normal number of chromosomes.

The male and female creeping vole mate as in other animals. The researchers have made the following discoveries about the species.

  1. Male creeping voles have two X chromosomes (XX). Females have one X chromosome (XO).
  2. Though the species lost its Y chromosome a long time ago, the current X chromosomes in both genders contain genes that were on the ancestral Y one.
  3. Females inherit their single chromosome from their mother, not their father.
  4. Although the X chromosome in the female’s cells contains genes from the ancestral Y chromosome, she doesn’t develop male characteristics.
  5. Males inherit one X chromosome from their mother and one from their father.
  6. The chromosome from the father is silenced (inactive) while it’s inside the cells of the son’s body.

Some intriguing questions are raised by the observations described above. For example, when an egg and sperm join in humans and most other mammals, the offspring receives one sex chromosome from each parent. The female creeping vole doesn’t have a sex chromosome that came from her father, however. It’s interesting to speculate about how the inheritance of the paternal sex chromosome is prevented.

The quotation below refers to another intriguing question about the creeping vole genome, or collection of genes. It refers to the ”expression” of a gene, or its activation. Even though a chromosome contains a particular gene, that gene may not be active at a particular time. Although the male and female vole both have X chromosomes, if significant genes on the chromosomes are silenced in one gender but not in the other, anatomical and physiological differences could appear.

In typical male development, the expression of a gene called SRY during a precise developmental window initiates the development of testes. Female voles carry 7 intact copies of SRY, Campbell and her team found. But somehow, the female voles silence these genes and all of their consequences.

— Stephanie Pappas, via Live Science, in reference to creeping voles

Another Source of Genetic Variability

Since the female vole gets her single chromosome from her mother, it might seem logical to assume that the mother and daughter are genetically identical. This is unlikely to be the case, however. As egg cells are being made, genes can be exchanged between DNA strands that are close together, creating variation. The process also contributes to the fact that the DNA in the sperm cells produced by a male vole are not genetically identical. Many sections are conserved in the DNA of eggs and sperm of an individual, however, which is why the offspring resembles a parent even though they aren’t identical to it.

Mysteries of Nature

The nature and behaviour of the sex chromosomes in creeping voles may sound very odd in comparison to the system in other voles and other mammals. One of the researchers studying the situation suspects that it may not be as unusual as it sounds, however. Researchers are slowly discovering additional oddities related to sex chromosomes in various mammals, including humans. We can also develop some unusual situations with respect to the identity of our sex chromosomes, though unlike the case in creeping voles this isn’t a routine occurrence in us.

The method by which the sex chromosome system in creeping voles developed is one of the fascinating mysteries of nature. As far as we know, the situation is different from that in other voles, which follow the normal mammalian pattern. Nature still contains many secrets. Exploring them is an interesting activity. The exploration may lead to important discoveries about genetics and heredity in other animal species and even in us.


  • Information about voles in the genus Microtus from the University of California
  • Creeping vole entry at NatureServe Explorer
  • Status of Microtus oregoni and information about the animal from the International Union for Conservation of Nature (IUCN)
  • Chromosomes fact sheet from the National Human Genome Research Institute (part of the NIH)
  • Creeping voles and the Y chromosome from Live Science
  • “Sex chromosome transformation and the origin of a male-specific X chromosome in the creeping vole” from Science (Abstract)

© 2021 Linda Crampton


Linda Crampton (author) from British Columbia, Canada on May 31, 2021:

I think voles are interesting creatures, too. The creeping vole is a fascinating species from a biological standpoint.

Mary Norton from Ontario, Canada on May 31, 2021:

Creeping voles, another interesting creature. I would label all the ones I see in the garden looking like this, groundhogs. Now, I'll be more discerning when I see a creature in the garden.

Linda Crampton (author) from British Columbia, Canada on May 29, 2021:

Thank you very much for the visit and the kind comment, Peg. I hope you have a great weekend.

Peg Cole from North Dallas, Texas on May 29, 2021:

So glad I found your article on the feed. As always, your information is interesting, educational and well-illustrated. Thanks for sharing in such a readable fashion.

Linda Crampton (author) from British Columbia, Canada on May 28, 2021:

Thanks for commenting when you found the article, Flourish. I’m most familiar with the vole species that live in my part of North America, but some species do live in other parts of the continent.

FlourishAnyway from USA on May 28, 2021:

I’ve been looking for this article to leave a comment. Glad it showed up on the feed finally. I found the description of the genetics very intriguing. I had thought we had these little rodents where I live but I don’t think they reach this far south based on your article. Must be moles instead that my cats occasionally kill and gift to me.

Linda Crampton (author) from British Columbia, Canada on May 27, 2021:

I’m looking forward to reading your article, Mel. I wish I could see moose in my backyard! I appreciate your visit and comment.

Linda Crampton (author) from British Columbia, Canada on May 27, 2021:

Thank you very much, Penny. It’s an interesting topic.

Mel Carriere from Snowbound and down in Northern Colorado on May 27, 2021:

This is fascinating stuff, and it would seem kind of science-fictiony if it wasn't actual science. Very soon I am going to publish another Lunchtime Lit about a book where people are ambisexual, meaning there are no males or females, and anybody can bear a child. If its author would have known about creeping voles in 1969, her science fiction would not have been really science fiction anymore, it would have been closer to the truth.

Anyhow, nature is a wonderful thing. On that note, I saw a moose crossing the road here in Northern Colorado day before yesterday. I know in Canada where you are they practically live in your backyard, but to me it was something special. That an animal so big can be so reclusive is mysterious.

Great article!

Penny Leigh Sebring from Fort Collins on May 26, 2021:

I saw a short blurb on this a few days ago, but it was lacking a lot of information. Thank you for writing this thorough and compelling piece.

Linda Crampton (author) from British Columbia, Canada on May 26, 2021:

Hi, Heidi. I agree with you. Nature is amazing! Thanks for the visit,

Heidi Thorne from Chicago Area on May 26, 2021:

Who would have thought a simple, common animal would be so complex from an evolutionary perspective? Nature is forever amazing. Thanks for sharing the world we often can't see!

Linda Crampton (author) from British Columbia, Canada on May 26, 2021:

Thanks, Eman. I appreciate your visit.

Eman Abdallah Kamel from Egypt on May 26, 2021:

It is really an interesting animal. Thank you, Linda, for all these facts about creeping vole.

Linda Crampton (author) from British Columbia, Canada on May 26, 2021:

That’s so true, Adrienne! There’s always something new to learn.

Adrienne Farricelli on May 26, 2021:

I didn't know voles are in the same family as hamsters. Always something new to learn!

Linda Crampton (author) from British Columbia, Canada on May 26, 2021:

I think it’s a fascinating topic, Peggy. Chromosomes and genetics are intriguing. I hope you have a good day.

Linda Crampton (author) from British Columbia, Canada on May 26, 2021:

I can understand why people confuse voles with mice, too. I appreciate your visit, Bill.

Linda Crampton (author) from British Columbia, Canada on May 26, 2021:

Thanks, Devika. I appreciate your kindness.

Linda Crampton (author) from British Columbia, Canada on May 26, 2021:

Thank you, EK. I hope you stay safe and healthy as well.

Thank you for the comment, Rozlin. I hope you have a good day, too.

Peggy Woods from Houston, Texas on May 26, 2021:

Whether voles or mice, their short lifespan enables scientists to do studies like this one about the chromosomes and genetics in multiple generations of them. I found this fascinating! Thanks for always educating us!

Bill De Giulio from Massachusetts on May 26, 2021:

Very interesting, Linda. I don’t think we have voles here in the northeast. I can see how people might confuse them with a mouse. Thank you for the education, I was not familiar with the vole.

Linda Crampton (author) from British Columbia, Canada on May 26, 2021:

Hi, Audrey. I think they’re cute, too. They are interesting animals. I appreciate your visit and comment.

Devika Primić from Dubrovnik, Croatia on May 26, 2021:

A well-written and informed hub about Creeping Voles. Linda you have such interesting hubs and always inform of us about something new. I enjoy reading and learning from your hubs.

Rozlin from UAE on May 26, 2021:

Hi Linda. It's a well explained hub on creeping voles. I learned a lot from your hub about voles. Thanks for sharing. Have a good day.

EK Jadoon from Abbottabad Pakistan on May 26, 2021:

You have shared some interesting facts about voles. Thanks for sharing the information with us.

Stay safe and healthy...

Audrey Hunt from Pahrump NV on May 26, 2021:

Creeping Voles are so cute! I enjoyed learning about them. So much to know about these little creatures. Very informative. Thanks.

Linda Crampton (author) from British Columbia, Canada on May 25, 2021:

Thank you for such a kind comment, Chitrangada. I appreciate your visit.

Chitrangada Sharan from New Delhi, India on May 25, 2021:

An excellent and well researched article about the Creeping Voles, and their unique characteristics!

I don't think I have seen them, or know about them

Your articles are always educative and informative and I am always happy to learn something new from them!

Thank you for sharing!

Linda Crampton (author) from British Columbia, Canada on May 25, 2021:

Thank you very much, Bill. Yes, I think many people may mistake a vole for a mouse. Some voles can be a nuisance, but I think they’re interesting animals.

Bill Holland from Olympia, WA on May 25, 2021:

Anyone who lives in the Pacific Northwest has seen a vole at one time or another, even though they probably thought it was a mouse. They were constant visitors when I was raising chickens. Great facts, as always. I always come away from your articles with great information.

Linda Crampton (author) from British Columbia, Canada on May 25, 2021:

I appreciate your visit and comment a great deal, Misbah. I hope you stay healthy and happy as well.

Linda Crampton (author) from British Columbia, Canada on May 25, 2021:

Thank you very much, Pamela. I’m always happy to discover a unique animal!

Misbah Sheikh from — This Existence Is Only an Illusion on May 25, 2021:

Linda, it is very interesting and informative article about Creeping Voles. I enjoyed reading about their behaviour, genetics and all the facts you mentioned. I never knew anything about them. If, I had seen it I would have called it mice.

Thanks for sharing. Stay happy and healthy

Blessings and Love

Linda Crampton (author) from British Columbia, Canada on May 25, 2021:

Thank you for the comment, Linda.

Pamela Oglesby from Sunny Florida on May 25, 2021:

This is a fascinating article Linda. I have never been around voles but I like learning about all creatures. Their chromosomes are sure unusual and they also don't live very long. They are uniquely different from many other animals. Thanks for sharing all this information.

Linda Chechar from Arizona on May 25, 2021:

I like so many the voles for your articles and images!