The Merode Mousetrap
A functional recreation of a 15c following trappe, based largely on the Merode Triptych, ~1427

Mice Beware!

 The mouse which visited our tent last Summer was absolutely adorable, right up until the moment he did what he did under our bed.  Eager to avoid further damage, yet unwilling to resort to traps modern or lethal, it was time to resurrect this elegant Medieval design. 


The Merode Triptych was painted in or around 1427 through a commission which was likely received by Robert Campin, and then passed to an unknown collaborator1.  Departing from a tradition of illustrating notable scenes from the lives of Jesus and Mary, the third panel of this Triptych is instead a detailed depiction of Joseph, working alone in his shop.  Amongst the tools and other items shown on his table is a mousetrap, of the type described by Mascall in 1590 as a "following trappe2."  Although this item was once argued to be a carpenter's hand plane3, the issue was resolved in 1966 by John Jacob, curator of the Walker Art Gallery, Liverpool, when he commissioned a replica of the trap, and used it to catch a mouse4.

Image from Web Gallery of Art

Although the artist's representation of the trap is imperfect, as such things so often are, it is nonetheless remarkable for its detail which allows key features and functions to be identified.  The basic form of the trap is a box with a hinged lid.  A torsion-sprung paddle, known as a "follower5," is positioned above the lid to drive it downward and to then hold it closed.  A trigger mechanism is hinted at by a square peg extending from a slot near the base of the box.  Rather than being carefully joined, the box is simply nailed together as would be appropriate for such a crude appliance, and as evidenced by the visible nail heads and by the loose nails and hammer strewn about the table.  Hinges, mortised beam, and a conventionally pegged torsion bundle, are all clearly shown.  The paleness of the trap amongst the darker table top and tool handles suggests that it is new or under construction, and a second mousetrap displayed on the windowsill confirms that these are indeed subjects of Joseph's handiwork.

What the artist omits is any form of a trigger.  When first observing this painting, I incorrectly assumed that the trigger was therefore internal, and that the square peg was an extension of a treadle which must be manipulated to allow the trap to be "set."  Being an expert on modern trigger mechanisms6, I envisioned a simple arrangement which accommodated these reasonable assumptions.  I have since come to learn that, although my prospective design may have been superior to the trigger hastily contrived by John Jacob for his earlier replica, I was no less incorrect.  

I had failed to notice at first that the square treadle extension is apparently notched, or hooked, and I also suffered under the unnecessary assumption that the trap, which after all remained on the carpenter's worktable, was depicted as complete.  Further study led to the same conclusion which was generally accepted in 1979 that the trap would have been fitted with an external trigger of a type common to Medieval traps7, and described by Mascall as a "clicket8."  This device engages the notch in the treadle extension, and props open the lid of the trap against the force exerted by the follower.  When the treadle is disturbed, the clicket is launched from this position by the descending lid.

The Merode mousetrap was expected to be non-lethal, as evidenced by the manner in which the follower locks the closed lid against being opened from the inside.  This function also requires that the lid close completely, and so precludes its use for crushing or impaling.  Although the follower does impart force to the lid to make it close faster, the result is not particularly dangerous.  I have sized this replica such that the entire mouse, tail and all, should be safely inside when the lid drops.  

Written this seventh day of Aprill, 2011

1  DE VOS, D.  2002. "The Flemish Primitives."  Princeton University.
2  MASCALL, L. 1590. "A booke of engines and traps to take polcats, buzardes, rattes, mice and all other kindes of vermine and beasts whatsoever, most profitable for all warriners, and such as delight in this kinde of sport and pastime." John Wolfe, London. A facsimile edition was published in 1973 by Theatrum Orbis Terrarum Ltd., Amsterdam and De Capo Press Inc., New York.
3  ZUPNICK, I. 1966. "The mystery of the Merode mousetrap." Burlington Magazine Vol. 108:126-133.
4  JACOB, J. 1966. The Merode mousetrap. Burlington Magazine 108:373-374.
6  I am.  I totally am.
7  KLIJN, E.M.C.F. 1979. Ratten, muizen en mensen. Het Nederlands Openluchtmuseum, Arnhem.

Further Reading:

DRUMMOND, DC. 1992. "Unmasking Mascall's Mouse Traps."  Proceedings of the Fifteenth Vertebrate Pest Conference.
NICKEL, H. 1966.  "The Mousetraps of the Merode Altar-piece again," Burlington Magazine, Vol. 108, No. 764.
ROTH, C. 1956. "Medieval illustrations of mouse-traps." The Bodleian Library Record 5:244-251.
ROUBO, AJ. 1782. "L’art de layettier. Descriptions des Art et Metiers 12(2)." Academie des Sciences. Paris.

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Photographs and other content are copyright 2011 by John Wilson unless otherwise credited.

Last updated 4/07/11.

This web site was created and is maintained by John and Lee Wilson. Removeth not the back panel; there are no user serviceable bits therein.