Collective Behavior of Worm Blobs

We study the aggregation of blackworms( Lumbriculus variegatus ) into large ensembles of entangled, living “blobs” composed of thousands of slender bodies knotted together. To understand the mechanism and advantages of aggregation in these worm blobs, we systematically expose them to various environmental stresses including light and temperature. The diameter of the worm blob can be controlled by both light stimulus history and light intensity. At low light intensity, the blob dilates; conversely, increasing the light intensity contracts the blob and leads to a more entangled and tightly packed state. This behavior also affects the collective movement under thermal stress. Under high light intensity (>1500 Lux) we find that a 5 g (~600 hundred) worm blob placed under a linear temperature gradient between 15 to 50°C stays as a blob and moves collectively to the cold side with a speed of 0.35± 0.01 cm/min. In contrast, if the light intensity is reduced to 400 lux, the worm blob dissipates and individual worms crawl to the cold side with a speed of 0.21± 0.03 cm/min. We find that the number of surviving worms increases when they move as a blob.