We observed the social behavior of the jumping spider, a common species of spider being found on board fences, earthen walls, etc. The spiders wander about within 2-3 m of diameters ranging on the surface of their habitat for a considerable period of time, when their population density is low without extraneous intervention, though some spiders may be observed to pass on. As the density becomes high, their behavior ranges appear to lie one on top of the other, but their individual positions are actually kept apart for more than a certain distance moment by moment. If they come within 20 cm with each other, they fight, with the result that the inferior spider escapes and that the required distance is restored again. So the dominant one has always a control over the subdominant within such a definite area and the dynamic equilibrium is kept during their continual migration carried on with a chain-reaction according to their social order. When the most dominant spider occupies the best position, it shows, though temporarily, the behavior like that of the trout (Plecoglossus altivelis), which has its own territory and home range. Experimentally we bred and observed the jumping spider in a cube-shaped glass box, and obtained almost the same results as could observe out doors. They wander about on the separate internal faces of the box while their population density is low. As the density becomes high, their behavior ranges apparently lie upon another, but they keep a definite distance from one another, except when they start fighting now and then. When the density becomes still higher, the inferior reduces its range of behavior, or stays in its nest, keeping quiet. The jumping spider, therefore, can be considered to have its behavior range, which is affected by its social order. But it may be said that the stability or fixity of their range of behavior is still in a weak stage in many ways.
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