ID question (House Mouse or E. Harvest Mouse)

Mouse_A

I caught this small mouse in an overnight sherman trap this morning (Georgia, USA) and would like to confirm ID. I tentatively identified it as a House Mouse based on the small size, relatively uniform coloration between dorsal and ventral, and the readily visible scales on the tail. However, after looking at some photos on the internet, I am a bit more uncertain and want to be able to rule out Eastern Harvest Mouse (my target species). Although my photo is pretty terrible you can see the scales on the tail easily although it did have sparse hair, how furred is the tail of a harvest mouse?  Is this a House Mouse or is the photo inconclusive? Also, for future references, what is the best way to separate the two species?

Mouse_1A

Mouse_1B

7 Comments
  1. Vladimir Dinets 5 months ago

    If I remember correctly, harvest mice have proportionally longer tails. Also, they don’t have the musky odor of house mice. But the 100% certain way is to take a pin and feel the backside of the upper incisors: in house mice they have a little step. Only mice of genus Mus have it. Here’s a picture: https://www.welcomewildlife.com/wp-content/uploads/2015/01/House-mouse_front_teeth-Magne-Flaten-Wiki-cc-by-sa-2.0.jpg

  2. Profile photo of Jon Hall
    Jon Hall 5 months ago

    I took a quick look in the field guide and in fact the Eastern Harvest Mouse has a shorter tail relative to house mouse. I think the easter harvest mouse should have a bicolour tail which your animal appears not to have but hard to say from the photo. I don’t think there is too much fur on a harvest mouse tail though …. its very hard to tell from your picture. It doesn’t look all that like a Mus to me but it doesn’t look all that like a Harvest Mouse either!

    As Vladimir said house mice teeth have a notch which you can see when you are holding them if you lift up the lip and turn the animal in profie. Harvest Mice also have particularly distinctive incisors with a groove up the front that can also been seen quite easily (I think the only genus in North America that has this). There is a picture here (about half way down the page) http://www.mammalwatching.com/places/colorado/

    Generally pictures of the tail, tail tip, length of tail relative to the body are all very helpful things to have when IDing small mammals

    Jon

  3. Author
    Marcus 5 months ago

    Thanks! As I have never handled rodents, what is the best way to go about checking their teeth without hurting the animal and not getting bitten? I had known about the groove in Reithrodontomys teeth, but not the notch in Mus, but at any rate had not known how to check it on a live animal. I’ll get better photos for next time, as they seem to be common in the patch of habitat I’ve been trapping, whatever it may be…

    Marcus

    • Profile photo of Jon Hall
      Jon Hall 5 months ago

      It’s not very hard to look at the teeth but it takes a bit of experience I suppose. I usually hold the animals by the scruff of the neck and use a pencil to lift the lips gently.

  4. Vladimir Dinets 5 months ago

    Just remember to wear gloves when you handle rodents, and keep them as far from your face as you can,.

    • Profile photo of Marcus Author
      Marcus 5 months ago

      Thanks Jon and Vladimir, I’m a bit leery about handling them and appreciate the advice. I do wish to get identification correct though. I’ll put out a trap tommorow night, as it will be the only warm one this week, and report back if I get anything

  5. Profile photo of Marcus Author
    Marcus 5 months ago

    To report back, I’ve made two successful captures over three trap nights. The first individual escaped from the bag before I could get a good grip on it, but I was able to grasp the second (perhaps the same one). However, I forgot the pin as suggested by Vladimir, or even a pencil with which to feel for the step on the back of the teeth. Despite that, it did appear that the step was present although not 100% certain as the mouse and its teeth were very small. I did not observe grooves on the front of the teeth either. So probably Mus. I’ve added two photos of this individual to the original post if you have any comments on whether it’s appearance is consistent or not with that ID. Thanks!

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