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Nature Notebook – Tarantula Molt

“Did we get a new tarantula?” That was the question when two tarantulas were spotted in Rosie’s cage.

Turns out we did have a new one…but it was a “new” old one. Rosie had shed (or molted). Arthropods, just like reptiles, shed their exoskeletons when those rigid coverings become too small or worn out.

Rosie prepared for the occasion by spinning a thick silk mat, which became her molting bed. Then she rested…sort of. During this time, the new exoskeleton was forming and molting fluid was being produced. The fluid oozed between the old and new exoskeletons. The fluid was reabsorbed just before the actual molt, which left an air space that allowed the two skeletons to easily separate.

Most spiders stop molting once they reach maturity because they don’t live much longer after that point. Female tarantulas can live for ten to twenty years and need to replace their worn out exoskeletons periodically. The shed provides an excellent opportunity to safely study the spider’s anatomy, including its formidable fangs.