The question of whether “daddy long legs” are poisonous to humans often receives a simplified answer. This widespread belief stems from a misunderstanding of the creatures commonly referred to by this name. Unpacking the science reveals a more nuanced truth about the actual risks they pose to people. Understanding their distinct biological characteristics is important to clarify this enduring misconception.
Identifying Daddy Long Legs
The term “daddy long legs” informally refers to at least two distinct types of arachnids, leading to much of the confusion. Harvestmen, belonging to the order Opiliones, are arachnids but are not true spiders. They possess a single, fused body segment, unlike spiders which have two distinct body parts. Harvestmen typically have two eyes, often located on a raised central tubercle on their oval-shaped body. They do not spin silk or construct webs, preferring moist, sheltered environments like under rocks or logs.
In contrast, cellar spiders, members of the family Pholcidae, are true spiders. They exhibit the characteristic spider body plan with a clearly separated cephalothorax and abdomen. Cellar spiders generally have eight eyes, often clustered, and are known for their exceptionally long, thin legs, which can be several times their body length. These spiders commonly build loose, irregular webs in undisturbed, often dusty, areas such as basements, cellars, and corners of rooms. Understanding these two groups is key to understanding their potential effects on humans.
Harvestmen and Venom
Harvestmen, despite their long legs, are not venomous or poisonous to humans. They do not possess venom glands, nor do they have fangs capable of injecting venom. Their mouthparts are chelicerae, which are small, pincer-like structures adapted for tearing food into smaller pieces.
These arachnids are primarily scavengers, feeding on decaying plant and animal matter, or preying on small, soft-bodied insects. When threatened, Harvestmen rely on defensive behaviors such as releasing foul-smelling secretions from scent glands or rapidly running away. Some species can also detach a leg to distract a predator, a process known as autotomy, allowing them to escape.
Cellar Spiders and Venom
Cellar spiders, unlike Harvestmen, are indeed venomous. Their venom, however, poses no significant threat to humans. The venom is relatively mild, primarily effective against their insect prey, which they often subdue by wrapping them in silk before biting.
While cellar spiders possess fangs, these are extremely small, typically measuring around 0.25 millimeters in length. A bite from a cellar spider is rare and usually results in only a mild, short-lived stinging or burning sensation, similar to a pinprick. Scientific studies and documented cases show no evidence of medically significant effects from cellar spider bites on humans.
The Enduring Myth
The persistent myth that “daddy long legs” are highly venomous but harmless due to small fangs is an urban legend that conflates different creatures and misinterprets spider biology. This misconception often arises from the general confusion between harmless Harvestmen and true spiders like cellar spiders.
Cellar spiders, despite their mild venom, are beneficial in many environments. They consume various household pests, including other spiders, which can help control insect populations. Harvestmen also play a role in their ecosystems as scavengers, contributing to decomposition. There is no scientific evidence to support the claim that any creature commonly called “daddy long legs” is dangerously poisonous to humans.