16.01.2021

The moult of a tarantula larva

The following video shows the molting (= ecdysis) of a spider larva into the 1st nymphal stage in fast motion. As the spider increases its blood pressure to about 300mm Hg and pumps large amounts of this body fluid into the cephalothorax, the carapace first tears open in the front just below the eye tubercle. The cephalothorax often achieves a weight gain of up to 80% due to this increase in blood pressure, while the opisthosoma becomes 30% lighter. Normally, the cuticle resists pressures up to 600 - 750mm Hg. However, due to the premature degradation of the endocuticle in preparation for the molting phase (= apolysis), the strength of the cuticle decreases by about one third and can thus tear much more easily. The tear then continues laterally at the carapace margin to the rear until the carapace folds up. As the blood pressure continues to rise and the exuvial fluid lubricates between the old and new skin, the legs slowly push out of the old skin. The spines on the legs also prevent the legs from sliding back. During this process, the thin skin of the opisthosma also tears open more and more, so that the spider comes completely out of the skin at the end.

Reference:

Foelix, R. (2010): Biology of Spiders. Oxford University Press