The term “daddy long legs” commonly refers to several distinct creatures, leading to frequent confusion about their biology. While the name is ambiguous, some of these animals shed their outer layer, a process known as molting, which is fundamental for growth. This article clarifies which “daddy long legs” species molt and explains the biological mechanisms.
The Biological Process of Molting
Molting, or ecdysis, is a biological process for arthropods, including arachnids and insects, to grow. Their rigid outer covering, an exoskeleton, does not expand with the animal’s increasing size. Shedding this non-living cuticle is essential for continued development and tissue repair.
Molting begins when the arthropod’s body releases hormones, such as ecdysone, signaling the need for a new exoskeleton. Enzymes then break down the inner layer of the old exoskeleton, allowing nutrient reabsorption. A new, softer, and larger exoskeleton forms underneath the old one.
Once the new exoskeleton is ready, the old one splits, typically along pre-defined lines of weakness. The animal extracts itself from its old shell, often by increasing body fluid pressure to expand and crack the exoskeleton. The newly emerged arthropod is soft and vulnerable until its new cuticle hardens, which can take hours to days.
Identifying the “Daddy Long Legs” That Shed
The common name “daddy long legs” refers to at least three different animals, and their molting habits differ by classification. Harvestmen (Order Opiliones) are arachnids, but not true spiders. They possess a fused body section and typically have two eyes, unlike most spiders. Harvestmen molt their exoskeletons as they grow, similar to spiders.
Cellar spiders (Family Pholcidae) are true spiders. Recognized by their long, thin legs and small bodies, they undergo molting to accommodate their growth.
Crane flies (Family Tipulidae) are insects, not arachnids, often mistaken for large mosquitoes due to their slender bodies and long legs. While they undergo metamorphosis (egg, larval, pupal, adult stages), their molting differs. The larval stage, “leatherjackets,” molts several times as it grows, but adult crane flies do not shed an exoskeleton like arachnids.
Life Stages and Molting Frequency
For harvestmen and cellar spiders, molting is primarily associated with juvenile growth. Young harvestmen typically undergo around six molts before reaching adulthood. Young spiders, including cellar spiders, molt multiple times as they increase in size. Some spider species may molt up to a dozen times throughout their lifespan.
The molting process can be energy-intensive and leaves the animal vulnerable due to its soft, unprotected new cuticle. After reaching sexual maturity, most adult harvestmen and spiders stop molting, though some adult spiders may continue less frequently.