The common name “Daddy Long Legs” causes frequent confusion because it refers to three entirely different types of arthropods globally, each having a distinct number of legs. Determining the true leg count requires examining the biological classification of the specific creature being referenced. The three primary contenders for the name belong to two separate classes of arthropods, leading to a difference in the number of appendages.
The Eight-Legged Arachnids
Two creatures commonly called “Daddy Long Legs” are arachnids, meaning they possess eight legs, the standard number for this class. The first is the harvestman, belonging to the order Opiliones, which is not a true spider. Harvestmen are easily identified because their two main body sections—the cephalothorax and the abdomen—are broadly fused, making their body appear as a single, oval structure.
Unlike true spiders, harvestmen do not possess venom or silk glands, so they do not spin webs to catch prey. They use their four pairs of legs for walking, though their second pair is often longer and utilized as sensory feelers. Over 6,650 species of harvestmen have been discovered globally.
The second eight-legged creature is the cellar spider, belonging to the family Pholcidae, which is a true spider. These arachnids have eight extremely long and thin legs in proportion to their small, typically translucent bodies. They are often found hanging upside down in the loose, irregular webs they construct in dark, quiet places.
Cellar spiders are distinct from harvestmen because their body is divided into two clear segments, a characteristic of all true spiders. They possess both venom and silk glands, though the venom is harmless to humans. When disturbed, they rapidly vibrate or bounce in their web, a defensive behavior that makes them difficult for predators to see.
The Six-Legged Insect
The third creature referred to as “Daddy Long Legs” is the crane fly, which is an insect, not an arachnid. Crane flies are classified in the family Tipulidae and are characterized by having six legs, the defining feature of all adult insects. As true flies, they belong to the order Diptera and possess a single pair of wings.
Crane flies have slender, mosquito-like bodies and long, fragile legs that break off easily as a defense mechanism against predators. They are often mistaken for giant mosquitoes, but they are completely harmless and do not bite. Most adult crane flies are short-lived and do not feed, existing only to mate and lay eggs.
Understanding Arthropod Anatomy
The difference in leg count is dictated by the fundamental rules of biological classification within the phylum Arthropoda. This phylum includes creatures with jointed legs and segmented bodies, and the number of legs is a primary characteristic used to group them into classes.
All arachnids, including the harvestman and cellar spider, are defined by having four pairs of legs, totaling eight. Conversely, all adult insects, such as the crane fly, are classified as hexapods because they have three pairs of legs, or six in total. This division based on appendage number provides a clear biological distinction that resolves the ambiguity of the common name.