The Mars Bar Mice

Some years ago, back in Ireland, I was contacted by the owner of a business located in the same business centre as my pest control company. We'll call him Paddy which wasn't his real name. Paddy told me that he was having terrible problems with mice at home. He said he was catching as many as 20 every night. Now, I have seen some heavily infested homes, but never one where that many were caught every night.

I queried these numbers and it transpired that Paddy had purchased 20 live capture mouse traps; his wife was "dead set against using poison, even if the mice were eating her cashmere sweaters to make a nest." Paddy had  been setting the traps all in his roof voids and around the house, baited with Mars bar. Each morning every trap had caught a mouse. "Big fat healthy mice!" said Paddy.

I asked Paddy what he did with the caught mice. "Oh. I take them way across the fields and let them go. About a kilometre away." he said.

I suggested that that night he set the traps again as usual. But next morning, mark each mouse with a dab of correction fluid before releasing them, and set the traps again for the following night.

Sure enough the second morning 20 'corrected' mice had been caught in the traps.

The mice were fat from Mars bar and fit from the exercise and fresh air they got each day making their way back across the fields to the house for another feed of Mars bar.

This wasn't quite the end of the story however. There was still the question of how the mice were getting back into the house. Paddy insisted that he had put much effort into finding and sealing all possible entry points. I agreed to visit the house and take a look.

It doesn't take much of a gap for a mouse to enter a building; a gap as narrow as a pencil is all they need, even well fed Mars mice. I was confident I would find a broken air vent, gap under a door, ill-fitting pipe, or climbing plant leading up to the eaves. But when I checked the house I could find no possible entry. It was unlikely that all the mice would be able to sneak in an open door when Paddy or his wife opened and closed them after themselves.

How could they be getting in?

A common entry point for rats and mice is via the garage if the garage is attached to the house. But Paddy's garage was 15 metres from the house. But I did find a gap under the garage door and I found little 'messages' letting me know that mice were getting into the garage.

In Ireland and the UK central heating is common in most homes to combat the cold, wind and rain. Rats and mice love the heat from central heating boilers and the pipes carrying hot water to radiators. The pipes can often provide highways for mice to travel around a building as the holes in walls and joists are rarely sealed tightly. This was how the mice were getting into the house. Paddy's central heating boiler was in the garage and the pipes ran underground to the house. the mice had followed the pipes, eating their way through the insulation around the pipes.

Once I sealed up the gaps around the pipes, and Paddy had caught and released the mice a long way (over 2km) away from the house, the problem was solved.

There are several lessons from this story:

• Mars bars and regular exercise make for big healthy mice
• You can train mice to get caught in traps
• Mice will find a way in if there is one
• Mice often follow pipes and cables
• You can keep mice out if you find and seal all the entry points
• Mice will find their way back to a home from over a kilometre away
• If releasing mice that you have caught in live capture traps, release them more than 2 km away (and not near other human habitation)
• Mice like Mars bars – other chocolate bars are likely to be equally attractive

David Brittain
Kiwicare