Mouses in Our Houses, Part 1

Mouses in our Houses (Part 1) 

What is it about the sight of a small furry grey creature scurrying across the bathroom floor, inches from your feet, that spikes an adrenaline rush? Your heart beats a mile a minute,  you run like a mad woman to the telephone to hire a pest control service.

Have our Cinderelly (think Disney fantasy) views of these rodents jaded our perception of these filthy rodents who have no qualms about fouling their nests, stockpiling food supplies in dark corners, and producing litters literally by the dozen? 

The life span of a mouse is five to seven years. A female mouse can produce three to fourteen young in three weeks, and do this five to ten times a year. There is no mousy-menopause. They never stop breeding! Even more frightening, it only takes four to six weeks for a newborn fluff ball to become sexually mature.

Let’s do some math, Mousy-Nerds!!!

Use conservative numbers: Start with one female mouse having a litter of ten babies, half of which are females. The females take 6 weeks to mature sexually, and only breed every other cycle.

Potentially, how many mice could you have after 4 months?

One pregnant mouse, call her Gen1, short for 1st generation. After three weeks, she could produce ten offspring (Gen2). Generous, but base 10 math means easier calculations. Let’s assume only half of them are female. Also assume that each female only breeds every other cycle, and none of her offspring die. Consider this a closed system. That means no other mice sneak into the house. I’m thinking loose morals, and mousy-incest is not prohibited in this hypothetical scenario. Furthermore, no cats exist in the household. 

Start the clock!

Sooo,  here’s the tally:

At 0 weeks:   1 pregnant, female mouse Gen1

1 mouse in my house.

At 3 weeks:  Gen1 produces 10 offspring, Gen2 has 10 members +Gen1 = 

11 mouses in my house, 5 males, 6 females, only one sexually mature and she needs a break.

At 6 weeks: No new offspring, 11 mice, 5 males, 5 sexually mature (and eager) Gen2 females, Gen1, takes a bye.

11 mouses in my house, but all 5 Gen2 females are pregnant. 

At 9 weeks:      Gen3 = 50 (Gen2 females each have a litter of ten) + 10 Gen2 + 1 Gen1 = 61 mice, 

31 females, 30 males. Gen1 is ready for motherhood again. Gen2 females on break.

There are now 61 mouses in my house. 

At 12 weeks:   Gen1 has 10 offspring (Gen4), Gen2 females are on break. Gen3 are not sexually  mature yet. 61+10 = 71 mouses in my house.

At 15 weeks:   No new offspring, All 5 Gen2 and 25 Gen3 females get pregnant, Gen1 on break, Gen4 not yet sexually mature. 

71 mouses in my house.

At 18 weeks:   Gen2 and Gen3 females have a total of 300 (!) offspring, Gen1 and Gen4 are ready to get pregnant.  

Total mouses in my house = 371 

The numbers are STAGGERING.  So, this happens after 126 days, about four months if the mousy mortality rate is zero.  I got carried away with the horror of it all. 

This scares the $%^&*out of me. And this all started with one pregnant mouse. And my assumptions are REALLY conservative. (Only one pregnant mouse makes it in the house. Pleassse….)

A humorous side does exist for this misadventure. More in Part 2 of the Mousy Adventures of a Physicist Turned Mystery Writer on Mouse Patrol. 

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