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Bug of the Week is written by "The Bug Guy," Michael J. Raupp, Professor of Entomology at the University of Maryland.

Destination Central Cordillera, Costa Rica: A visit with giant rainforest recyclers, Polydesmid millipedes


Python millipedes are striking recyclers of vegetation in the rainforest.


Over the past several weeks we’ve escaped the dreary, chilly confines of Maryland to visit denizens of tropical rainforests in Costa Rica where we met orb weaving spiders, stingless bees, velvet ants, and tiger beetles. We’ve discovered their important ecological roles and learned where they fit into the circle of life in one of the most diverse biomes on planet earth. Today we will meet charismatic recyclers of rainforest vegetation that go by the intriguing names of tractor millipedes, python millipedes, and giant flat-backed millipedes. One can easily see where these monikers originated. An encounter in the dim light of the rainforest with these large colorful forest floor dwellers could startle one in much the same way as an encounter with a reptile might. Flattened dorsal plates surely describe a flat-backed arthropod reminiscent of the tread of a tractor tire moving across the forest floor. Simple eyes, touch, and smell guide the millipedes’ quest to find delicious rotting organic matter that serves as their tucker. 

Dozens of tiny legs move in synchronized waves to propel the tractor millipede as it searches for food on the rainforest floor.

Millipedes play an essential role in the ecology of rainforests and other ecosystems around the globe where they recycle vegetation, making the energy and nutrients found in plants available to other living organisms. Millipedes and their cousins, centipedes, are not insects but belong instead to a group of arthropods called the Myriapods, “many legged creatures”. Contrary to their name, millipedes do not actually have one thousand legs. If one were to buy shoes for all of their tiny feet, between 40 to 400 pairs would do the trick depending on the species. Most body segments of millipedes bear two pair of legs rather than a single pair as would be found on centipedes. This is an easy way to tell centipedes from millipedes next time you happen on one in the garden.

Curling into a tight ball is a common defense of millipedes.

How do animals so large and apparently so defenseless protect themselves from hungry predators? The primary defense of millipedes is to curl into a tight ball and protect their tender underbelly. Plates on their back and sides are sturdy and are believed to withstand hungry beaks and jaws. Many species of millipedes also wage chemical warfare against lethal attackers. Glands line the margins of the millipede’s body and when provoked by a predator, these glands secrete a veritable witches’ brew of noxious chemicals such as hydrogen cyanide, benzaldehyde, phenol, benzoic acid, benzoyl cyanide, and mandelonitrile. These chemicals are repellent and act as deterrents to insects, birds, or other small animals attempting to munch on a millipede. Although Costa Rican tractor millipedes are mighty impressive with a body length of roughly six inches, the real leviathans of the millipede realm reside in tropical Africa forests where they bulldoze through leaf litter and soil in search of decaying plant material. At more than 15 inches, these behemoths dwarf their Costa Rican cousins. However, fossil remains of a relative called Arthropleura have been found in Nova Scotia. This giant was roughly eight feet long. Imagine encountering one of those while wandering through the rainforest at night!


The interesting article “Defense mechanisms of Nyssodesmus python (Polydesmidae)” by Sheiphali Gandhi, and the fascinating book "For Love of Insects" by Tom Eisner were used as references for this episode.