▶ All arthropods (insects, spiders and crabs) have a hard exoskeleton, which they must shed at intervals, to catch up on their growth. Known as ecdysis (from the Greek ekduo to strip off), the process is carefully coordinated, risky in the wild, and fraught with difficulties.
▶ For several days or even weeks before the molt, a tarantula will appear moody and sluggish, refusing to eat. It spins a cradle, called molting web (seen to the left of the gif), and lays on its back. Its heart rate increases dramatically and hemolymph (“blood”) is pumped into the upper body (cephalothorax) so it nearly doubles in size. The pressure cracks the carapace along the sides and front. Wave like muscle contractions in the abdomen push the old exoskeleton, lifting it off like the lid of a can. Now comes the tricky part: the spider must work its legs out of the old shell, with forward facing hairs and bristles keeping it from slipping back inside.
One well-placed kick, and the ordeal is over – here, have a cigar!
♺▶ Fun Facts (aka everything you wanted to know about molting but were afraid to ask):
● Before the molt, the spider secretes a digesting fluid that loosens and eats away at the old cuticle (yum!).
● While spiderlings molt several times a year, mature females, who can live up to 40 years molt every other year. Unfortunately, many males do not survive their last adult molt, because their male sex organs get stuck in the exoskeleton (sorry, guys!).
● The molt lasts from ~20 minutes, in babies, to several days in the adult (ladies, you sympathize, right?).
● During a molt, spiders also shed their fangs, chelicerae (which they use for grasping), their throats and stomach lining, female genital organs (omg!), and the lining of their “book lungs”.
● A spider that has lost a leg can regenerate one during a molt.
Credit: This has been a fun Google+ #collaboration with the lovely Carmelyne Thompson for #ScienceEveryday . Carmelyne gif-ed the ecdysis time-lapse for this post, after we discussed another cool spider molt gif on her post (http://goo.gl/fVo5fp). If you don’t have Carmelyne in your circles for more science fun, you should!
More reading: http://goo.gl/U6w0cV