The Molting Behavior of the Black Widow Spider, Latrodectus mactans1

Abstract

The molting behavior of Latrodectus mactans (F.) involves a complex series of innate stereotyped movements. The spider hangs beneath the web during the molting process, attached by 4 pairs of legs and the spinnerets. The premolting twitches of the legs at the coxal joints begin at least 2 hr prior to the molting process. This process begins with the spider attaching its spinnerets to the webbing and then swinging the legs inward and attaching them along a central line. A downward pressing motion against the carapace of the old cuticle finally produces a lateral split just above the coxal joints. During the downward pressing motion the abdominal muscles begin an undulating motion which carries the abdominal skin toward the spinnerets. After the carapace of the old cuticle is free, a downward pulling motion is initiated to remove the legs from the old cuticle. Once the legs are free they hang straight out parallel to the ground and the old cuticle. The legs while in this position are pulled laterally in a separating motion, being relaxed after each small gain and falling back to a more central position. The legs are finally pulled to the sternum and a transverse pulling motion is begun. The right and left legs are rolled alternately forward and back in opposite directions prior to each pull. The legs are pulled more dorsally and finally reach out to grasp the web. After several minutes the spider turns and moves a short distance in the opposite direction as it releases the spinneret attachment.