7 Mar 2018

Inventor turns compost bin to rat trap

From Jesse Mulligan, 1–4pm, 1:37 pm on 7 March 2018

Rats kept getting into Hannah Smith’s home-made compost bin. When none of the traps she tried solved the problem she invented her own.

Smith tried a variety of traps – from the snap traps though to through to high-tech CO2 canister-driven models.

Manufacturers told her to set traps away from the compost pile, because no bait would be more enticing for a rat than the heap itself.

“So it seemed like a good idea to try and make the compost pile the bait,” Smith says.

She tried putting a trap in the wall of the home-made bin, but decided she needed to build a trap from scratch.

After a few “pretty hilarious” attempts she came up with a combination rat-trap compost bin made from a recycled washing machine drum, that also incorporates the dead rats into the compost.

The drum is set on a frame, allowing it to be turned like a rotary or tumbler compost system. The difference is there’s a rat-sized entrance to the unit, which allows the rodents easy access. But the exit is fitted with a snap trap to snare them.

When the unit is reset the rat falls into the compost, which is later dropped into the box below. It sits directly on a raised bed or the ground.

The compost doesn’t smell, Smith says. “Because of the really rich mix of microbes all going crazy in that lower bed, I’ve dropped rats into it and … it doesn’t smell at all, they just disappear really quickly.”

Rat-trapping runs in the family; Smith’s father James Wilson is involved in Picton Dawn Chorus, the community effort to control predators in Picton / Waikawa.

The prototype of her invention under the working title ‘urbin composter’, is online.

Smith will make the plan available online for anyone who wants to make one - the whole unit is made of a single sheet of plywood and the drum -  and build and sell them herself.

“My back yard is filling up with washing machine drums – my husband’s not entirely enthused about it.”

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