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Expert Opinion

All In A Day's Walk
By Dr. Stuart Mitchell

For any given pestiferous ant, "all in a day's work" is all in a day's walk. One reason for the astounding biological success of ant species is their terrestrial travel talent. With three pairs of podites positioned laterally for potent posture, the ant's body has a low center of mass to maximize strength of stance. Serving as a brace and a lever each podite or leg holds and distributes the ant's body weight as well as enabling its ambulation.

Used by most terrestrial arthropods, ants use a metachronal (beating of a group) wave or gait. Within this gait a podite lifts only when the preceding podite is in contact with the surface (a position of support). The wave initiates from the back as the hind podite lifts and is transferred forward then each podite lifts in turn.

In walking mode or smooth movement gait only one podite at a time is lifted while five podites remain in contact with the surface. Increased stability and decreased energy expenditure result.

In running mode or tripod gait three podites move simultaneously. The ant consistently has three podites in contact with the surface. On one side of the body; front and hind podites touch the surface while on the opposite side of the body; the middle podite touches the surface. For alternating tripods of support to work, six podites are required.

Neuronal networks control podite articulations. Neuronal networks are central pattern generators (CPGs) that produce rhythmic pattern outputs without rhythmic sensory or central input. Researched as models of neural network function, central pattern generators cause the production of many rhythmic motor patterns.

Each podite has one or more CPGs. Interneurons link singular networks and CPG outputs are altered per podite sensory feedback.

Movement by tripod gait is only possible by animals with an inelastic frame. Insects with soft bodies such as larvae have a hydrostatic skeleton. Movement is through peristalsis or contractions that propagate waves down a tube coupled with other means.

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