The urban myth that “daddy long legs” are among the most poisonous spiders but cannot bite humans is a widespread misconception. Understanding their true nature reveals why this popular belief is incorrect.
Unpacking the “Daddy Long Legs” Term
The term “daddy long legs” causes confusion because it refers to two distinct arachnid groups: harvestmen (Opiliones) and cellar spiders (Pholcidae). Both are arachnids, but they differ significantly in anatomy and biology.
Harvestmen are not spiders. They have a fused body structure, appearing as a single, oval-shaped segment, unlike spiders which have two distinct body parts: a cephalothorax and an abdomen. Harvestmen also possess only two eyes, compared to the eight eyes most spiders have. They do not produce silk for webs, and their mouthparts are designed for chewing and scavenging, not for injecting venom.
Cellar spiders, often found in homes, are true spiders. They exhibit the typical two-part body structure and spin irregular, tangled webs. These spiders have small bodies and exceptionally long, thin legs, which can span up to two inches. They are often mistaken for harvestmen due to their similar long-legged appearance.
The Reality of Their Venom and Fangs
Harvestmen and cellar spiders differ significantly in venom and biting ability. Harvestmen do not possess venom glands, meaning they cannot produce or inject venom. Their mouthparts, sometimes described as fang-like, are chelicerae designed for grasping and masticating food, not for piercing skin.
Lacking venom, harvestmen pose no threat to humans. They are primarily scavengers, feeding on decaying plant matter, fungi, and small, soft-bodied invertebrates. If disturbed, some species can release foul-smelling defensive chemicals from glands to deter predators, but this is a defensive secretion, not an injected venom.
Cellar spiders possess venom glands and fangs. However, their venom is very weak and is not medically significant to humans. Studies indicate cellar spider venom is of low potency, even against insects, and poses no danger to human health.
Their fangs are small, typically measuring around 0.25 millimeters. While some research suggests they are capable of penetrating human skin, any bite would likely result in only a mild, localized irritation, comparable to a mosquito bite or a slight sting, with no lasting effects. Cellar spiders are timid and prefer to retreat rather than bite, making actual bites rare.
Why the “Most Poisonous” Claim is False
The claim that “daddy long legs” are the most poisonous spiders but cannot bite humans is a widespread urban legend with no scientific basis. The myth conflates two different arachnids and misrepresents their biological characteristics. Harvestmen are not venomous at all, possessing neither venom glands nor fangs capable of injecting toxins.
Cellar spiders, while venomous, have venom that is remarkably weak and poses no significant threat to humans. Their small fangs, though technically capable of skin penetration, deliver venom not potent enough to cause harm. This contrasts with medically important spiders like black widows or brown recluses, which possess potent venom capable of causing severe reactions.
The origin of this myth may stem from observations of cellar spiders preying on more dangerous spiders, like redback spiders, in their webs. This led to the mistaken assumption that cellar spiders must possess an even more potent venom to overpower such formidable prey. In reality, cellar spiders often use their long legs and silk-wrapping abilities to immobilize prey rather than relying solely on venom.