While boating around Elk Horn Slough last spring we saw a pile of sea lions sleeping on the water’s edge. Sea lions are thigmotactic, the naturalist told us, which means they like to lie all over each other. Later we saw harbor seals basking in the sun. They were in a group, but each had its own space, about a foot from neighboring harbor seals. Harbor seals are not thigmotactic, the guide told us. (1)
Or maybe they are just less thigmotactic. It’s probably more a matter of degree. Thigmotaxis is a response to contact often referred to as “wall-hugging behavior” to describe animals that like to avoid being out in the open. When insects creep under the bark of a tree for the winter or mice run along the walls instead of out in the middle of the room they are exhibiting positive thigmotaxis. Staying near the edges even has a genetic component. Some mice hug walls more than others and mice can actually be bred for wall-hugging behavior. (2, 3)
In a broader sense, the term thigmokinesis refers to how an organism’s movement is affected by contact. In plants this is called thigmotropism, the response that peas or morning glories make when their tendrils find a support to cling to. As with animals, this trait is crucial to survival.
When one harbor seal gets too close to another, his neighbor moves away. On the other hand, sea lions enjoy lying around in overlapping piles. In some animals thigmotaxis is related to a need for warmth and protection for the vulnerable. Baby mammals like puppies or kittens seek contact with their mother but eventually begin to wander off on their own. As adults, they may tend to keep their distance from each other, but they still seek security by curling into a cozy bed or lying close to a trusted friend. (4) My little rescue dog Ozzie stays in direct contact with me whenever he can. Even at day camp he likes to stay near familiar dogs until he sees me coming to pick him up.
Thigmotaxis has even been studied in humans. The amount of personal space we prefer varies individually as well as with the culture we live in. A recent article states that extreme thigmotaxis in humans may even be related to agarophobia, a pathologic fear of open spaces. This finding was based on an “open field” study of peoples’ behavior outdoors in a field bordered by trees as well as in an open marketplace, in which people who suffered from agarophobia stayed near the edges. (5,6)
But many of us have a perfectly natural tendency to stay close to the edges, for example at parties or in an empty restaurant. How architects use this knowledge is explained in a book called Cognitive Architecture, by Ann Sussman and Justin B. Hollander, who state, “We navigate more like rats and mice than we may think.” It is the principle behind “double-loaded corridors,” a concept seen in bazaars and malls, where the shoppers stay along the edges. City planners who do not take this behavior into account create empty public spaces. (7)
Thigmotaxis. We all have it and it affects our everyday decisions. How much is all a matter of degree.
With gratitude to:
- Elk Horn Slough: http://www.elkhornslough.org/
- “Behavioral Responses in Mice Selectively Bred for High and Low Levels of Open-Field Thigmotaxis,” Pia k. Leppanen, 2009.
- The Ecology of Insect Overwintering, S.R.Winter, K.F.A.Walters, J.S. Bale, Cambridge University Press, 1995. P. 21 – 22.
- Handbook of Applied Dog Behavior and Training, Procedures and Protocols, Steven R. Lindsay, John Wiley & Sons, 2013. (no page numbers).
- “Fear of Open Spaces May Be Linked to Animal Instincts,” Wall Street Journal, 19, 2016
- “A Human Open Field Test Reveals Thigmotaxis Related to Agoraphobic Fear,” Biological Psychiatry, Sept. 1, 2016. Nora Walz, Andreas Muehlberger, Paul Pauli.
- Cognitive Architecture: Designing for How We Respond to the Built Environment, Ann Sussman, Justin B. Hollander, Routledge, 2014. Chapter 2: “Edges Matter: The Wall-Hugging Trait.”