House spiders, such as the common house spider (Parasteatoda tepidariorum) and the cellar spider (Pholcus phalangioides), are frequent indoor residents. While many people associate these arachnids with catching flying insects like houseflies and mosquitoes, this food source is seasonal or scarce in the controlled environment of a home. Their survival indoors depends on a specialized diet of non-flying prey. This need for alternative sustenance has led house spiders to become opportunistic predators, adapting their feeding habits to the unique ecosystem of a human dwelling.
Primary Alternative Prey
When flies are not available, house spiders sustain themselves by preying on the small, crawling arthropods that live within a structure. They target tiny household pests that often go unnoticed by humans. The size of the potential meal is the main limitation for the spider, meaning they focus on smaller organisms.
The diet often includes various types of mites, such as dust mites and clover mites, which are abundant but nearly invisible to the naked eye. Spiders also readily consume springtails, which are minute, wingless arthropods often found in moist areas like bathrooms and kitchens, feeding on mold and decaying matter. These tiny organisms provide a steady, consistent food base throughout the year.
Larger prey items like silverfish, which are elongated, nocturnal insects attracted to paper and starchy materials, become substantial meals. Spiders will also target the nymphs of larger pests, such as cockroach nymphs, which are small enough to be subdued. The larvae of certain beetles, including carpet beetles, also get caught in webs, providing a protein-rich meal.
Intraspecific and Opportunistic Feeding
House spiders have evolved several less conventional feeding strategies to endure periods of food scarcity.
Scavenging
One of the most significant is scavenging, where spiders will consume insects that have already died, often those that have expired in the web or nearby. Many spider species are capable of feeding on dead prey, a flexible behavior that provides calories without the energy expenditure of a live hunt.
Cannibalism and Oophagy
Cannibalism, or intraspecific feeding, is another common behavior, particularly when resources are limited. This can involve a female consuming a male after mating, or the predation of smaller, neighboring spiders by larger rivals. This behavior provides a high-quality nutrient source and reduces competition for the limited food supply. Oophagy, the consumption of eggs, is also observed, where a female may consume some of her own unfertilized eggs to recycle nutrients if her body reserves are low.
Surviving Periods of Scarcity
When the food supply is nearly nonexistent, house spiders rely on their unique physiology to survive. Spiders are not endotherms, meaning they do not expend energy to maintain a constant body temperature. This allows them to possess a naturally low metabolic rate, which is the primary factor enabling them to go for extended periods without a meal.
Smaller house spiders can survive for several weeks to a few months without food. In times of severe scarcity, some species can enter a state of dormancy, or diapause, significantly slowing down their activity and metabolism to conserve energy reserves. This physiological shutdown allows them to endure harsh, lean conditions, such as the depths of winter. Even during these long fasts, a spider’s survival is critically dependent on water. Access to moisture is constantly required to prevent desiccation, which is a much more immediate threat than starvation.