Giant house spiders feed primarily on flies, beetles, and small wasps or ants that blunder into their funnel-shaped webs. Research on the genus Tegenaria, which until recently included today’s giant house spider (now classified as Eratigena atrica), found that short-bodied flies, beetles, and members of the ant-and-wasp order made up the bulk of their captured prey.1PubMed. The prey of web-building spiders compared with feeding experiments That said, their diet is more flexible than a simple list of insects suggests, and the way they catch and process a meal is worth understanding on its own.
The Typical Prey Lineup
If you could inventory everything a giant house spider catches over a season, you would find it dominated by three groups. The first is short-bodied flies, the kind you might see on a piece of fruit or circling a kitchen light. The second is beetles, from tiny carpet beetles to slightly larger ground beetles that wander indoors. The third is small members of the order that includes ants, wasps, and sawflies. Longer-legged, slender-bodied flies like gnats and mosquitoes turn up much less often in their webs, probably because those insects are light enough to bounce off or escape the relatively coarse sheet web a giant house spider builds.1PubMed. The prey of web-building spiders compared with feeding experiments In homes, this translates to a practical roster: houseflies, cluster flies, small moths, earwigs, woodlice, silverfish, and the occasional ant column scout. The spider does not specialize. It is a generalist predator that eats whatever stumbles into its funnel.
Compared with orb-weaving spiders that hang delicate, sticky spirals in mid-air and intercept large numbers of tiny flying insects, the giant house spider’s sheet-and-funnel design catches fewer but somewhat larger individual prey items.1PubMed. The prey of web-building spiders compared with feeding experiments The web acts less like a fine-mesh net and more like a trip-wire platform: an insect lands on the broad sheet, loses its footing, and the spider rushes out from the funnel retreat to grab it.
How the Funnel Web Works as a Hunting Tool
Giant house spiders belong to the funnel weaver family Agelenidae, and their webs are central to how they eat. The web is a flat or slightly concave sheet of non-sticky silk that narrows at one end into a tube where the spider hides. When an insect walks or crash-lands onto the sheet, it does not stick. Instead, it struggles on the uneven surface, and that movement sends vibrations along the silk threads toward the spider. The spider interprets those vibrations to figure out roughly where the prey is, then sprints across the sheet to tackle it.
Research on how web-building spiders locate prey through silk vibrations shows that the radial threads radiating from the spider act like antennae. In one study, the thread carrying the strongest vibratory signal reliably predicted the direction the spider would turn, meaning the spider was consistently orienting toward the loudest “signal” in its web.2PubMed Central. Unsupervised discovery and predictive sensorimotor transformation of spider prey capture through active vibration sensing Separate modeling work on orb webs confirmed that a spider can reconstruct the approximate position of a prey impact from the vibration patterns picked up by its legs.3Scientific Reports. Prey localization in spider orb webs using modal vibration analysis While those particular studies focused on orb weavers, the underlying principle applies broadly to web-building spiders: silk threads carry mechanical information that the spider reads like sonar. For a giant house spider sitting deep inside its funnel, this vibration-sensing ability is the difference between eating and going hungry, because it cannot see prey well from inside the retreat.
Speed matters once the spider commits. Giant house spiders are famously fast runners for their size, and the flat sheet web gives them an unobstructed runway. They do not need to climb a vertical web or reel in a struggling insect on a sticky spiral. They simply dash out, grab the prey, and haul it back into the funnel to feed in safety. This sprinting ability also lets them overpower insects that would otherwise escape a non-sticky web.
What Happens After the Catch
Spiders do not chew. A giant house spider’s mouthparts cannot break food into chunks the way a beetle’s jaws can. Instead, it relies on a process called extra-oral digestion, which is essentially digesting the prey outside of its own body. After biting the prey and injecting venom that paralyzes or kills it, the spider floods the wound with a cocktail of digestive enzymes. These enzymes dissolve the soft tissues of the prey into a liquid slurry. The spider then pumps that liquid into its gut, regurgitates more enzyme fluid back into the carcass, and repeats the cycle. The prey’s exoskeleton effectively becomes a bowl in which digestion takes place.4PubMed Central. Characterisation of protein families in spider digestive fluids and their role in extra-oral digestion
The enzyme cocktail is not simple. It includes protein-breaking enzymes, fat-breaking enzymes, and enzymes that break down nucleic acids and carbohydrates. The spider pumps and sucks the fluids back and forth repeatedly to mix the enzymes and dissolve as much tissue as possible.4PubMed Central. Characterisation of protein families in spider digestive fluids and their role in extra-oral digestion Research on related species has shown that some of these enzymes work best in an alkaline environment and handle the initial external breakdown, while another set of enzymes works inside the spider’s gut cells in an acidic environment, handling a second round of digestion after the liquefied food is swallowed.5PubMed. Cysteine cathepsins as digestive enzymes in the spider Nephilengys cruentata
This is why, if you find a dead insect beneath a giant house spider’s web, it often looks eerily intact on the outside but hollow. The spider has sucked out everything soft and left behind little more than a shell.
How Prey Size Affects What Gets Eaten
Giant house spiders have a leg span that can reach about 75 millimeters, with a body length up to roughly 18 millimeters for large females. That makes them among the largest spiders found in northern European and North American homes. Their size means they can tackle prey that smaller house spiders cannot, but there are still limits. Feeding experiments across multiple spider species found that the sweet spot for prey acceptance sits between about half and four-fifths of the spider’s own body size. Prey much larger than the spider is almost always rejected, with only a couple of species in those experiments willing to attack prey twice their own size.6Springer Link / Oecologia. A comparison of prey lengths among spiders
For a giant house spider with a body around 15 millimeters long, this means it comfortably handles prey in the 8-to-12-millimeter range: houseflies, small moths, modest beetles, earwigs. It can manage larger items occasionally, but acceptance drops off quickly. Very small prey like fruit flies or springtails are not usually worth the energy expenditure of a sprint across the web, though a hungry spider will eat just about anything it can subdue.
Juvenile giant house spiders, being much smaller, eat correspondingly smaller prey. Their webs are finer and placed in tighter crevices, and their menu leans heavily toward tiny flies, mites, and springtails. As they grow through successive molts, their prey range shifts upward in size. This developmental scaling means that a single species effectively fills multiple ecological niches over its lifetime, competing with different sets of predators at each stage.
Do Giant House Spiders Eat Other Spiders?
Yes, and this is one of the more practical reasons people tolerate them indoors. Giant house spiders are known to prey on other spiders that share their habitat, including smaller funnel weavers and cellar spiders. This is not specialized predation; it is opportunism. If another spider wanders onto a giant house spider’s web or into its territory, it gets treated the same as any other appropriately sized prey item.
There is a persistent claim that giant house spiders have displaced false widow spiders in parts of the UK. The evidence for systematic competitive exclusion is thin, but individual predation events certainly happen: a large Eratigena will kill and eat a smaller Steatoda if the two cross paths. In a home with an established giant house spider population, smaller spider species tend to be less visible, whether because they have been eaten, outcompeted for web sites, or simply deterred from settling nearby.
Cannibalism also occurs. Females occasionally eat males, particularly after or even during mating. Males are smaller and spend the autumn wandering in search of mates, which means they frequently stumble into the webs of other giant house spiders. If the resident spider is hungry and the intruder does not signal its intentions quickly enough, it becomes a meal rather than a mate.
Are They Picky About Nutrition?
The old assumption was that spiders are pure opportunists, eating whatever falls into the web without regard to nutritional content. That picture has been revised. Research on multiple spider genera has shown that different spider groups, and even different sexes and life stages within the same species, end up with nutritionally distinct diets. Some spiders disproportionately catch prey rich in fats, while others favor protein-heavy prey, and these patterns are consistent enough to suggest active selection rather than random chance.7Oikos. Prey nutrient content is associated with the trophic interactions of spiders and their prey selection under field conditions
Controlled experiments with wolf spiders showed that when fed prey with varying ratios of fat to protein, the spiders adjusted both how much they ate and how efficiently they converted ingested nutrients into body tissue. When the available prey was protein-heavy, the spiders ate more of it in an apparent attempt to obtain enough fat, overconsumming protein in the process. They also processed protein less efficiently when it was overly abundant, a way of buffering their body composition against an unbalanced diet.8Animal Behaviour. Nutrient regulation in a predator, the wolf spider Pardosa prativaga Those experiments used wolf spiders rather than giant house spiders, but the underlying ability to partially regulate nutrient intake appears widespread among spiders.
What this means for your house spider is that it is not just eating mindlessly. If it has been catching a lot of lean, protein-rich prey like ants, it may be more inclined to attack a fat-bodied moth next. The regulation is imperfect, and body composition still shifts depending on what is available, but the spider is doing more metabolic bookkeeping than its reputation as a brainless predator would suggest.
How Indoor Lighting Changes the Menu
If you have noticed that spiders seem to build webs near porch lights and illuminated windows, you are observing a well-documented phenomenon. Artificial light at night draws flying insects, and spiders exploit that concentration of prey. A field experiment comparing lit and unlit bridge panels found that spiders in artificially lit areas caught more prey and had better body condition, even though they built smaller webs. Interestingly, fewer spiders set up shop in the lit zones, possibly because the light also attracted the spiders’ own predators, like birds.9PubMed Central. Orb-weaving spiders are fewer but larger and catch more prey in lit bridge panels from a natural artificial light experiment
For giant house spiders living indoors, the dynamics are slightly different. They tend to build in dark corners, behind furniture, and in basements or garages, not directly in lit areas. But the insects drawn indoors by your house lights often end up wandering into those dark corners. A moth that flies through an open window toward a lamp eventually flutters down to rest, and if it lands near a funnel web, its fate is sealed. The spider benefits from your lights without ever sitting under one.
Seasonal shifts in indoor insect populations also change what the spider eats. In autumn, cluster flies and crane flies become abundant indoors across temperate regions, and they show up heavily in funnel webs. In summer, smaller flies and moths dominate. In winter, prey becomes scarce, and giant house spiders can fast for weeks or even months. Their metabolic rate is low enough to survive long stretches without food, though they will lose body mass steadily until prey reappears.
When Prey Is Contaminated
One dimension of a spider’s diet that most people never consider is what happens when the prey itself carries chemical residue. In agricultural settings, insects that contact pesticides before being caught by a spider can transfer those chemicals during feeding. Research on a farmland spider species showed that when prey had been exposed to neonicotinoid pesticides, the spiders killed the contaminated insects but then refused to eat much of them. In females of the study species, the rate of “overkilling,” meaning killing the prey without actually consuming it, jumped dramatically when the flies had been treated with neonicotinoids.10PubMed Central. Prey contaminated with neonicotinoids induces feeding deterrent behavior of a common farmland spider
This finding suggests spiders can detect something off about contaminated prey after initial contact and choose to abandon it. From the spider’s perspective, this is a defensive behavior. From an ecological perspective, it is troubling: the spider wastes energy catching prey it then discards, and if the contamination is widespread, the spider’s effective food supply shrinks. For giant house spiders in homes, the practical parallel involves indoor insecticide use. If you spray for ants or flies and a spider later catches a dying, pesticide-laden insect, the spider may eat less of it, or the chemicals may accumulate in the spider’s body. This is one of the underappreciated consequences of using broad-spectrum insecticides indoors.
The Role of Venom in Subduing Prey
Giant house spiders are venomous, as virtually all spiders are, but their venom is not medically significant to humans. Its purpose is prey capture. The venom acts fast on insects, causing paralysis that prevents the prey from struggling and escaping the web or injuring the spider with its own defenses. Research comparing paralysis and lethality across spider venoms found that the two properties scale together in a roughly linear way: venoms that paralyze more efficiently also kill more effectively.11PubMed Central. Paralysis efficiency (PD50) scales linearly with lethality (LD50) in spider venoms For a giant house spider, quick paralysis is especially important because its web is not sticky. Without adhesive silk to restrain the prey, the spider relies on speed and venom to close the deal before the insect can scramble off the sheet.
Venom also serves as the opening act for digestion. The same bite that delivers neurotoxic compounds to paralyze the prey can introduce early-stage digestive enzymes, beginning the tissue breakdown before the spider even starts pumping its main digestive fluids.4PubMed Central. Characterisation of protein families in spider digestive fluids and their role in extra-oral digestion This head start on digestion is especially useful for larger or more heavily armored prey, where the spider needs the exoskeleton to soften before it can extract much nutrition.
Can They Eat Anything Bigger Than Insects?
Occasionally, spiders eat vertebrates. A comprehensive review of spider-versus-vertebrate encounters documented cases across dozens of spider families, and the funnel weaver family Agelenidae, which includes giant house spiders, was among those recorded feeding on small vertebrates.12The Journal of Arachnology. Spiders feeding on vertebrates is more common and widespread than previously thought, geographically and taxonomically These events typically involve very small vertebrates, such as tiny lizards, frogs, or juvenile mice, that happen to wander into a large spider’s web or hunting ground. The review characterized such feeding by Agelenidae and similar families as opportunistic chance events rather than a normal dietary pattern.
For a giant house spider in your home, the realistic version of this is vanishingly rare. A newborn mouse or a very small gecko might theoretically be vulnerable, but these encounters almost never happen in domestic settings. The spider’s day-to-day diet remains firmly in the realm of arthropods. The vertebrate-feeding data is more interesting as a window into spider capabilities than as a description of what your house spider actually eats. It does, however, underscore how effective the combination of venom, extra-oral digestion, and silk restraint can be: the same system that dissolves a housefly can, under the right circumstances, handle prey far above the spider’s usual weight class.
Living with a Resident Predator
Giant house spiders eat many of the insects that people find annoying indoors: flies, moths, earwigs, ants, and even other spiders. A single large female with a well-placed web can catch dozens of insects over a season. Whether that is enough to noticeably reduce your indoor insect population depends on how many entry points your house has and how many spiders are present, but the effect is real. People who remove all spider webs from their home sometimes notice a bump in other small arthropods, particularly in basements and garages where funnel weavers concentrate.
If you want to coexist with your spiders but draw a line somewhere, the webs in high-traffic areas can be swept away. The spider will usually rebuild nearby or relocate. Spiders in out-of-the-way spots like behind the water heater or under a workbench are purely beneficial, eating pests you would never otherwise notice. The one caveat worth mentioning is that if you use indoor insecticides, you are likely harming these natural pest controllers along with their prey. Given the evidence that spiders detect and avoid contaminated insects, even sub-lethal pesticide exposure disrupts their feeding behavior. In a home where insect control matters to you, the spider in the corner may already be doing part of the job.