This report deals with the structure, the formation and the dissolution of winter colony in the first stadium larva of Atypus karschi DOENITZ kept in a laboratory. 1. Though adults in the field never form the colony, larvas form it in winter when a large number of them are put together in one breeding farm. But even adults in a laboratory have a tendency to form the colony if they are left for long time in one breeding farm. 2. They crowd in radiate around a few bodies that will be called nucleus bodies. In this way the winter colonies are formed. And its structure is sometimes flat and sometimes heaping. All the nucleus bodies do not always stay there so long but some of them do so as long but some of them do so as long as they like. The small colonies are easy to be dissolved, and yet non radiate crowding colonies are easier to be dissolved. Therefore the colonies of radiate structure or large colonies are not dissolved easily. The winter colonies of adults often become the radiate structure. 3. We can see the corner effect and the border effect on the winter colonies of larvas kept in the glass. 4. Atypus begin to have the active moving at near 18°C and at upper 37°C have heat coma and them die. 5. They begin to form the colonies when the temperature becomes lower gradually, and at under 5°C at least, within 12 hours they form the fixed colony. The formation of colonies takes these steps, first “free movement”, then “gathering”, then “movement between the colonies” and “the fixedness”. In this process some small colonies are dissolved and mingled with the large colonies unstably. While the large colonies are usually stable. 6. Even the fixed colony sometimes moves. The movement often happens in high temperature circumstance, seldom in low temperature. 7. There are two Ecological factors of formation and dissolution of colony. They are temperature and the social interference. 8. The abdomen of Atypus in dissolving colony becomes smaller, so the yolk quickly decreases. The decrease of the yolk is a physiological factor to make the colony dissolve.