Analysis of the Movement of Two Silkworms during the Construction of Double Cocoons

Abstract

In a few genetic strains of the silkworm, Bombyx mori, two mature larvae jointly spin a large cocoon called a double cocoon with a high frequency. We measured the behaviour of the silkworm to spin double cocoons and analysed the data to examine the relationships between the two silkworms concerning the sharing of the cocoon construction, the relative positions of the two silkworms, the moving properties and the spinning speed. As a result, we were able to visually show the spinning positions and the sharing of the two silkworms for the construction of the cocoon. The results showed that they fixed their bodies in the same or opposite direction with a high frequency. Furthermore, in one race of double cocoons, pseudo-periodicity existed in the serial change of the angle between the two silkworm bodies. There was a difference between the transition probabilities of the two different kinds of double cocoons. The behaviour of one silkworm affected the movement of the other silkworm in one of the double cocoons, though the two silkworms behaved more independently in the other double cocoon. They moved the spinneret significantly faster when the hind parts of the body were being fixed than when they were moving, although there was no definite difference between the spinning speed of the two silkworms.