Harvest mice as pets

The Basics

Harvest mice (Micromys minutus) are the smallest British rodent. They are tiny, native mice with long, prehensile tails, and fully grown weigh only 4-6 grams and are just 5 to 7 cm long. They have white fur on their bellies and brown fur on top and are very agile, using their tails for balance as well as hanging onto things. The typical photos of Harvest mice (as below) show them sitting on or eating ears of wheat, but in fact they eat a wide variety of seeds, shoots, insects and fruit – they have to be flexible in their appetites as the decline of traditional farming methods means that dropped cereal grains/field margins are scarce. In the wild, harvest mice are very low on the food chain with everything from foxes and owls down to large toads finding them a tasty snack or meal. By necessity, they are therefore shy creatures and extremely hard to spot in the wild. This means that keeping track of wild populations is very difficult, but they are thought to be in decline.

I have been keeping Harvest mice for around 4 years and have found them to be entertaining, curious and relatively low maintenance 'pets'. My interest in them was sparked after watching a youtube video of several young harvest mice playing in a wheel and pinging out of it. I currently have a vivarium of young female mice and several regularly pile into their wheel and ping each other out while it spins.

Habitat

I keep my Harvest mice in tall glass vivariums (30 x 30 x 45 cm) with mesh tops and opening hinged doors at the front. On the base I put about and 2 inches of sawdust or similar (I have read that you should not use sawdust for them – but I do and see no harm from it) you can also use hay, grass, moss and chipped bark on the bottom of their habitats. They will rapidly create little tunnels and nests within this substrate – which is entertaining to see through the glass. I give my mice lots of things to climb up (as they love climbing) and currently have given them 'first floors' made from bark/wood sitting on top of strings (natural garden twine) held onto the glass sides by suckers with hooks. They also love to have plenty of fresh and varied things from the garden: flowers, unripe seeds of all kinds (dandelions before they open are very popular), and are especially fond of the tender shoots of grass (grab a handful for them and the pale bases are rapidly eaten) and any mosses you can find. I also give them twigs to climb up, leaves, interesting pieces of rotting wood and anything interesting and ideally a little smelly as they seem to be largely led by their noses. I try to regularly add little bits from the garden as they seem to enjoy the natural smells so much. I also give my mice lots of kitchen roll/loo roll tubes, and a 'silent spinner' wheel in each tank. They love their wheels and seem to find them fun to use. Sometimes there's almost a waiting line of mice (I think the dominant mice get first dibs), at other times several mice compete to make the wheel turn in their preferred direction by climbing up the sides to gain advantage. Sometimes I see them use the moving wheel as an elevator/travellator – they seem to understand how the wheel works and enjoy the exercise and options it provides. In terms of cleaning out, I have read online that 4 times a year is sufficient, (but I wonder about the nasal capacity of that person, as the mice rapidly build up a distinctive smell), however, I keep my mice in my living room and find I can get away with leaving it about 6-8 weeks or so before cleaning them.

Diet

Their diet is mainly a mixture of as many types of birdseed I can find, and I put strings of millet hanging from the mesh ceilings, which they adore. They are also partial to black sunflower seeds, which they seem to enjoy releasing from their shells and then eating rather like a corn in the cob (their little paws holding each end). In the less natural line, I have found Harvest mice to be fond of cucumber, tiny pieces of twiglets, wholemeal bread, raw or cooked pastry, freshly cooked (not salted or sweet) popcorn, prawn crackers, cream and cheese. Oddly, my mice seem not very fond of berries and fruit. They quite like to eat the squishy flesh from grapes (leaving the skin), but are totally uninterested in blackberries, hawthorn berries and even strawberries and raspberries. I am not sure if they eat them in the wild when seeds are less available, or whether my lot are just oddly fussy.

Interaction

I do not believe that keeping Harvest mice in captivity has a very great impact on their wildness, and to a certain extent they tolerate human intervention rather than becoming greatly changed by them (although I do believe a few of them seem to enjoy being played with, but this might be purely my imagination). I do handle my mice (they are more than able to avoid you if they don't want to be picked up), and have a few of both sexes that are happy to be picked up and taken to my back door for some lungfuls of fresh air. Older mice seem to be more reluctant than younger mice, but if varies. Some of my mice have developed a funny but cute habit of sitting on my hand (often with their tails curled around my fingers) and then deciding to run up my arm and sit on the back of my neck (very ticklish). If they get comfortable there (for example if wearing a roll-neck jumper) they will sometimes stay there and fall asleep (maybe it's like a heated blanket/bed?). However, they are very adept at pretending to be well behaved, and then legging off to explore the house. If this happens, they run around the edges of the room and find a piece of furniture to hide underneath. I have found AWOL mice playing in the fake coals of my gas fire, sleeping in the narrow gap behind a cupboard about a foot off the floor, upstairs in my bathroom, and playing behind my cooker. However, generally they make their way to the baskets of mouse food and make enough noise when they're bored to allow me to pick them up and pop them back home. I also have a humane mousetrap which comes in handy when they're being awkward.

Sleeping

Harvest mice build themselves small spherical nests from grass, moss or unravelled twine. They often sleep together in piles, especially when young, sometimes perched precariously (and I find it amusing when one mouse halfway down decides to shift making the whole mouse-stack reorganise).

Breeding

Harvest Mice are very good at breeding in captivity, and given half a chance would constantly be at it. I have a suspicion that it might be possible for females to store semen up so they can produce two litters with no male contact after the first litter (but there might have been a segregation error). My mice have had between 5 and 7 babies. The female will build a larger spherical nest, and gradually become infeasibly bulky until she looks like two ping-pong balls with a head. She withdraws and gives birth to the 'pinkies' (tiny hairless, blind squishy things) inside the nest. She then feeds them up over the next 11 days as they develop fur and sight, before they hesitantly emerge from the nest on day 12. They are tiny, wobbly and entertainingly rubbish at balancing initially, and provide great entertainment. Mother mouse gets fairly bored of her duties a few days later, when they are able to fend for themselves. I discovered the hard way that mice over about a year old become infertile.

Sexing

Sexing harvest mice is very difficult due to their tiny size, their speed of movement and the fact their bits do not develop visibly until after they are already sexually mature. The technique I use is to put them onto a cooling rack (metal grid), and lift them up high so I can see their underneaths as they move. Generally, they will stretch out a little quite soon, and either tiny nipples (two rows), or a slightly squarish rear end will become apparent. I try to do this before they are 2 weeks old, and then keep the sexes segregated unless I decide some lucky mice can breed.