The common fear that spiders lay eggs under human skin is a widespread misconception, not based on scientific reality. Spiders do not and cannot lay eggs inside a human body.
Spider Biology and Human Skin
Spiders possess an anatomy that prevents them from laying eggs under human skin. Their chelicerae, or mouthparts, are designed for injecting venom or defense, not for burrowing or depositing eggs. Spiders lay their eggs in protective silk sacs, typically in webs, under leaves, or in soil, environments suitable for development.
The structure of human skin acts as a barrier against such intrusion. The outermost layer, the stratum corneum, prevents foreign substances and organisms from entering the body. This layer, composed of tightly packed cells and lipids, forms an effective defense. The human body’s internal environment also lacks the oxygen and conditions necessary for spider eggs to survive and hatch.
What Can Happen Under the Skin
While spiders do not lay eggs under human skin, several real conditions can cause skin lesions or sensations that might be mistaken for such an event. Scabies, for instance, is a highly contagious skin infestation caused by microscopic mites that burrow into the superficial layer of the epidermis to lay eggs. This results in intense itching and a pimple-like rash.
Other possibilities include parasitic infestations by fly larvae, such as the human botfly, which can create a painful nodule under the skin as the larva develops. These larvae enter through a bite wound or hair follicle, and the sensation of movement can be felt. Bacterial skin infections, which can manifest as red, swollen, and painful bumps often filled with pus, might also be misidentified.
Understanding Spider Bites
Spider bites are typically defensive, not aggressive. Spiders usually bite humans only when threatened, such as when accidentally trapped against the skin. Most spider bites are harmless, causing only minor local reactions like redness, swelling, or mild pain, similar to a mosquito bite or bee sting.
Severe reactions to spider bites are rare and associated with specific species, such as the black widow or brown recluse spiders. Even then, the bite causes localized tissue damage or systemic symptoms from venom, not egg implantation. Many skin irritations and lesions are frequently mistaken for spider bites, when they are actually caused by other insects, allergies, or bacterial infections.