The term “daddy long legs” is confusing because it refers to three entirely different creatures that share the common trait of having long, thin legs. This ambiguity often leads to questions about their behavior, especially why one of these organisms frequently appears indoors. Understanding which creature you are seeing is the first step to knowing why it is in your house and how to manage its presence. This article will clarify the identity of these long-legged visitors and explain the specific environmental factors that attract them inside human dwellings.
The Three Creatures Known as Daddy Long Legs
The most common indoor resident is the Cellar Spider (Pholcidae), which is a true spider with two distinct body segments and eight eyes. These spiders are famous for spinning large, tangled, irregular webs, typically in the corners of rooms. While they possess venom glands, their fangs are generally considered too small and their venom too mild to pose any threat to humans.
Another creature bearing the nickname is the Harvestman (Opiliones), a member of the arachnid class but not a true spider. Harvestmen are easily distinguished by their single, fused body segment and lack of venom glands or silk-producing organs. They use small, pincer-like mouthparts to scavenge for decaying matter and small insects, posing no danger to people or pets.
The third animal is the Crane Fly (Tipulidae), which is an insect and not an arachnid at all, sometimes mistakenly called a “mosquito hawk.” Crane flies have six legs, a pair of transparent wings, and a delicate body, resembling an oversized mosquito. Adult crane flies are entirely harmless, as many species do not even possess mouthparts for feeding, living only briefly to reproduce.
Environmental Factors That Attract Them Indoors
The primary cause for an indoor presence is the Cellar Spider, which seeks the stable, non-fluctuating environment of a human structure. These spiders prefer areas that offer protection from intense cold or heat found outdoors, using basements, crawl spaces, and dark closets as year-round refuges. The consistent temperature allows them to thrive and reproduce without the seasonal dormancy required outside.
High humidity is a major attractant for Cellar Spiders, as they require moisture to prevent desiccation and maintain their reproductive cycle. They are often found in parts of a home where humidity levels exceed 50%, such as damp basements or utility rooms with plumbing leaks or poor ventilation. This dampness encourages the growth of mold and mildew, which in turn feeds smaller insects that become prey.
The availability of food is the determining factor for a sustained population, as Cellar Spiders are opportunistic predators. They feed on a variety of small insects, including gnats, flies, and even other spiders. If a home has a secondary pest issue, the Cellar Spiders will move in to take advantage of the reliable, sheltered food source.
Managing and Preventing Indoor Presence
Reducing the interior humidity is the most effective way to make an environment less appealing for Cellar Spiders and their prey. Running a dehumidifier in damp areas like the basement or crawl space helps to maintain a relative humidity level below 50%, which is generally unfavorable for these spiders. Fixing any leaking pipes or ensuring proper ventilation in bathrooms and laundry rooms also eliminates sources of excess moisture.
Mechanical exclusion is an important step to prevent their initial entry into the home from the surrounding outdoor environment. This involves sealing cracks and gaps in the foundation, especially where pipes and utility lines enter the structure, using a durable silicone-based caulk. Installing tight-fitting screens on all foundation and attic vents, and ensuring that all windows and doors have intact weatherstripping, eliminates potential entry points.
Control efforts should also focus on eliminating the spider’s food supply and existing population. Regularly vacuuming up webs, spiders, and egg sacs in corners and undisturbed areas removes the current generation and their potential offspring. Reducing clutter in storage areas, like boxes and old clothing piles, eliminates the dark, quiet hiding places where they prefer to build their webs and wait for prey.