Ambiguous Visual Controls

Ambiguous Visual Controls: Come Closer. No, stay Away!

By Jon Miller Updated on May 19th, 2017

Peter Köves shared an amusing example of this ambiguous or perhaps downright dangerous visual control.

When hiking in the countryside of South Limburg near the Dutch city of Maastricht, I stumbled upon this sign on the side of the path:

The sign reads:
“Watch out!
Oak processionary caterpillar
To prevent health troubles we advise you to observe the following ‘code of conduct’:
– Don’t go standing under an oak tree or sitting in the grass under it.
– Avoid touching the caterpillars, the nests and the tree trunk.
– Avoid eyes contacting the urticating hairs.
– Provide good cover of the neck, arms and legs.
– Look for treatment of discomforts in case of skin or eye contact on or ask your doctor.
(Municipality of Valkenburg aan de Geul)”

The suggestions on this sign are certainly reasonable. The problem is: The sign is placed underneath an oak tree!

Have you ever seen similar well-intentioned but perhaps dangerous warning signs?

How could we provide better warning against the health risks of the caterpillar?

  1. John Santomer

    August 23, 2009 - 5:54 am

    I noticed my niece having a good time watching the Little Red Riding Hood Cartoon spoof yesterday and it made me remember your blog.
    LRRH, as we can call her, came to her grandma’s cabin – not knowing of course it was the wolf already in her grandma’s bed waiting for her. LRRH told the wolf, “Oh grandmother what big eyes you have!”. The wolf answered her, “The better to see you with my child.” LRRH again added, “Oh grandmother, what big teeth you have!” The wolf answered quickly, “The better to eat you with my child!” And he grabbed LRRH and swallowed her in one gulp.
    If the trees are well apart, perhaps a perimiter fence may deter the people to get closer to the tree. Caterpillars are not known to crawl more than an inch a second and will not be more likely to target pedestrians or on lookers by intent. A likely probable chance of the caterpillar dropping off from the tree branches because of strong wind gusts in the vicinity can cause it to fall on any on looker. But a similar sign a few meters away from the tree on the path leading to it may advise people of the danger ahead.

  2. Peter Köves

    September 1, 2009 - 1:05 am

    since I provided the story and the picture I should give some additional facts:
    – the tree stood right at the side of the path.
    – pouncing ‘pillars are not the main risk. The urticating hairs which can cause rashes and other allergic reactions remain not just on the caterpillars or in their nest but can break away easily, become airborne and be carried away by the wind.
    – These hairs can keep their toxicity over years so that they accumulate in the area around a tree.
    When trees near populated areas are infested, the infestation has to be controlled with some sort of flame thrower.

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