1. A descriptive model for the walking patterns of eight-legged animals similar to one applicable to some insects is presented. Data from films of walking tarantulas are compared to the gaits predicted by the model.
2. The model is found to be inapplicable to the tarantula data in two important respects. Some of the common walking patterns of the tarantulas are not predicted by the model, and the several patterns found are not correlated with frequency differences.
3. The tarantula gaits are best described in terms of the phase-relationships between leg pairs. Bilaterally opposite legs and segmentally adjacent legs tend to be used in antiphase. There is much phase variation, giving different stepping sequences, but this variation is by and large not correlated with speed.
4. Incapacitation of some of the spider's legs results in adaptive changes in phase-coupling between the other legs.
5. A mechanistic model which could explain both insect and spider data is tentatively suggested. It is based on negative coupling between the oscillators controlling each leg.