Cellar spiders are enthusiastic predators of other spiders, and spider-eating is not a rare or accidental behavior for them. The common cellar spider Pholcus phalangioides, familiar to anyone who has noticed long-legged spiders dangling in messy webs in basements and garages, actively invades the webs of other spider species and feeds on the occupants. Researchers have documented this behavior in detail, including a surprisingly sophisticated hunting strategy that involves tricking other spiders into thinking they have caught prey.
How Cellar Spiders Hunt Other Spiders
What makes cellar spiders remarkable is not just that they eat other spiders, but how deliberately they go about it. Pholcus phalangioides does not simply stumble into another spider’s web and overpower it. The cellar spider enters the web of another species and performs specialized vibrations on the silk, mimicking the signals of trapped prey. The resident spider, feeling these vibrations, approaches as if it were about to grab a meal and instead becomes one.1Journal of Zoology. The biology of Pholcus phalangioides (Araneae, Pholcidae): predatory versatility, araneophagy and aggressive mimicry
This tactic is called aggressive mimicry, and it is one of the more cunning strategies in the spider world. Rather than relying on brute force, the cellar spider exploits the prey-catching instincts of its target. The victim spider is adapted to rush toward vibrations in its own web because those vibrations normally signal food. The cellar spider hijacks that instinct. By the time the resident spider realizes something is wrong, it is already under attack.
In addition to invading webs and eating the spiders living in them, cellar spiders are opportunistic about what else they find. They sometimes consume the eggs of other spider species and will eat insects that happen to be stuck in the alien web.1Journal of Zoology. The biology of Pholcus phalangioides (Araneae, Pholcidae): predatory versatility, araneophagy and aggressive mimicry The cellar spider does not go to the trouble of entering a rival’s web and then leave half the food behind.
The Wrapping Attack
When a cellar spider engages prey, whether it is another spider or an insect, the attack itself relies on a distinctive technique: wrapping. Rather than delivering a quick bite and waiting for venom to take effect, cellar spiders rapidly throw silk over the prey to immobilize it. If you have ever seen a cellar spider in its web vibrating wildly while something thrashes nearby, you have likely witnessed this wrapping behavior in real time. The spider spins the prey while casting silk over it, bundling it into a package before delivering a bite.
Research into the silk glands of Pholcus phalangioides has revealed that this wrapping process is more complex than it looks. Cellar spiders use multiple types of silk-producing glands during predation, combining different fiber types rather than relying on a single gland for a single purpose.2Journal of Experimental Biology. Functional diversity and behavioural use of fibre-producing silk glands in Pholcus phalangioides This flexibility in silk use may help explain why cellar spiders can subdue prey that seems too large or too dangerous for such a delicate-looking spider. The wrapping restrains the prey first, reducing the risk of a counterattack before the cellar spider commits to a bite.
This approach gives cellar spiders an advantage against other spiders specifically. Spiders are fast, armed with their own venom, and accustomed to being the predator rather than the prey. Trying to simply bite a spider that is fighting back would be risky. Wrapping it first neutralizes the danger. The combination of aggressive mimicry to lure the prey in close and rapid silk-wrapping to immobilize it before biting makes the cellar spider a surprisingly effective spider hunter despite its fragile build.
Which Spiders Do They Target?
Cellar spiders are generalists. Their diet includes both insects and other spiders, and they do not appear to specialize in hunting one particular spider family. In homes, they have been observed preying on a range of house-dwelling spiders. Anecdotal reports from homeowners and pest control professionals frequently describe cellar spiders occupying the webs of previously resident spiders after apparently eating or driving off the original owners.
The aggressive mimicry strategy described in the research literature works on any spider whose web relies on vibration-based prey detection, which includes most web-building species. This means cobweb spiders, funnel weavers, and other species commonly found in human dwellings are all potential targets. The cellar spider’s generalist approach to spider predation, combined with the fact that it thrives in the same indoor environments as many other house spiders, puts it in frequent contact with potential prey.
There is a popular claim that cellar spiders regularly kill and eat brown recluse spiders or even black widows. While cellar spiders certainly can and do kill other spider species, the idea that they serve as reliable biological control agents against medically significant spiders is not well supported by controlled research. A cellar spider in the right place at the right time might catch a recluse or a widow, but counting on it as a pest management strategy would be optimistic.
Cannibalism Among Cellar Spiders
Cellar spiders do not limit their spider-eating habits to other species. Cannibalism plays a real role in their ecology, and researchers have studied the conditions under which it occurs and how cellar spiders manage to avoid eating their own offspring.
A study examining two pholcid species found that cannibalism and intraguild predation provide important resources and influence how different predator species interact. When researchers tested whether mother cellar spiders would eat their own young, the answer was clear: mothers did not prey on their own spiderlings. However, unrelated adult females of the same species would eat spiderlings that were not their own.3The American Midland Naturalist. Kin Recognition in two Species of Cellar Spiders, (Pholcidae), and its Effects on Inter- and Intra-Specific Predation of Spiderlings
The findings revealed an interesting asymmetry between two closely related species. Pholcus phalangioides showed relatively consistent predation rates regardless of whether the spiderlings offered to it were conspecific or from the other species. But the other species tested, Pholcus manueli, ate P. phalangioides young at roughly twice the rate it ate its own species’ young, treating heterospecific spiderlings much like it would a cricket.3The American Midland Naturalist. Kin Recognition in two Species of Cellar Spiders, (Pholcidae), and its Effects on Inter- and Intra-Specific Predation of Spiderlings This difference suggests that intraguild predation, where two competing species prey on each other’s young, could be an important factor in determining which species dominates a given area.
The ability of mother cellar spiders to recognize and spare their own offspring is significant. Without some form of kin recognition, a spider that shares its living space with its own babies and regularly eats small spiders would quickly decimate its own reproductive success. The research confirms that this recognition mechanism exists and functions reliably under laboratory conditions, even after mothers and spiderlings were separated and then reintroduced.
The Venom Question
A persistent myth holds that cellar spiders possess extremely potent venom but cannot deliver it effectively because their fangs are too short to pierce human skin. This claim has been repeated so often that it has become one of the most widespread pieces of spider misinformation. The reality is less dramatic on both counts.
Research on the venom of a related pholcid species, Physocyclus mexicanus, tested the actual potency of crude venom using bioassays on crickets. The effective paralytic dose came out to about 3.9 micrograms per gram of body weight, which is comparable to that of other related spider taxa and not exceptionally potent by spider standards.4PubMed Central. Not so Dangerous After All? Venom Composition and Potency of the Pholcid (Daddy Long-Leg) Spider Physocyclus mexicanus The venom did produce flaccid paralysis and some localized darkening in crickets, effects not seen with the venom of another comparison species, which suggests pholcid venom has a somewhat distinct mode of action on invertebrate prey. But “distinct” is a long way from “the most dangerous venom in the world.”
As for biting humans, cellar spiders can do it. Documented bites on people result in a mild sting with no lasting effects.4PubMed Central. Not so Dangerous After All? Venom Composition and Potency of the Pholcid (Daddy Long-Leg) Spider Physocyclus mexicanus Their fangs are not too short to break skin. The myth probably persists because it is a satisfying story: the idea that the most dangerous spider in the world is the goofy, spindly one hanging in your basement has a certain appeal. But the science does not support it.
What the venom findings do help explain is how cellar spiders manage to subdue other spiders that might seem like tough opponents. Their venom does not need to be record-breakingly potent. It just needs to work well enough on invertebrate prey, and combined with the silk-wrapping strategy that immobilizes the target first, it clearly does.
Why Cellar Spiders Are So Good at This
It is worth stepping back to appreciate just how many things work in the cellar spider’s favor when it hunts other spiders. They are not physically imposing. Their bodies are small relative to their leg span, and they look like they would lose a fight with almost anything. Yet they consistently prey on spiders that are stockier and, in many cases, carry more potent venom.
Several factors combine to make this possible. Their extremely long legs allow them to keep their body at a distance while throwing silk, reducing the chance that prey can land a counterattack. The aggressive mimicry strategy means they often catch their target completely off guard. The wrapping-first approach neutralizes the victim’s own weapons before the cellar spider moves in for a bite. And the fact that they build messy, tangled webs rather than organized orbs may actually be an asset: the irregular structure is difficult for other spiders to navigate, giving the cellar spider a home-field advantage if a confrontation happens on its own turf.
Their willingness to eat other spiders, combined with their comfort in human-built environments, also gives them a competitive edge in the long game. When two spider species share a habitat, the one that eats the other has an obvious advantage. Over time, in a basement or garage, a population of cellar spiders can gradually reduce the numbers of competing species through direct predation. This is not a planned campaign; it is just what happens when an opportunistic predator lives alongside its food supply.
Living with Cellar Spider Predators
If you find cellar spiders in your home and are wondering whether to leave them alone, their spider-eating habits are often cited as a reason to keep them around. There is some practical logic to this. A cellar spider population in a basement will reduce the number of other spiders sharing the space, simply by eating them. If your concern is the total number of spiders in your home, though, the cellar spiders themselves are still spiders, so you are really just trading several species for one.
Cellar spiders are harmless to people. Their bites are trivial, their webs are messy but easily swept away, and they do not damage structures. They are also poor candidates for seasonal invasion because they tend to stay put once established in a sheltered indoor space. If your main concern is aesthetically unpleasant cobwebbing, cellar spiders will make it worse, not better, since their webs accumulate over time as old ones are abandoned and new ones are built nearby.
For people dealing with more concerning spiders like brown recluses, removing clutter, sealing entry points, and using sticky traps are far more reliable approaches than hoping resident cellar spiders will handle the problem. Cellar spiders will eat other spiders they encounter, but they cannot seek out and eliminate an entire population of recluses hiding in boxes and wall voids. Their predation is opportunistic and localized to the area around their web, not systematic.
How Pholcid Identity Confusion Muddles the Story
One complication in understanding cellar spiders is that the common name “daddy long-legs” is applied to at least three completely unrelated groups of creatures: pholcid cellar spiders, harvestmen (which are arachnids but not spiders), and crane flies (which are insects). This confusion fuels myths and muddled claims about venom, diet, and behavior. When someone says “daddy long-legs eat other spiders,” they could be talking about cellar spiders, which genuinely do, or about harvestmen, which are scavengers with a completely different biology and no venom glands at all.
Harvestmen look superficially similar to cellar spiders because of their long legs, but they lack silk glands, do not build webs, and are not predators in the same sense. They feed mainly on decaying plant and animal matter. Crane flies, meanwhile, are flying insects that do not eat spiders or much of anything else as adults. The overlap in common names means that accurate information about cellar spider predation often gets mixed together with irrelevant facts about these other animals, creating a tangle of folk wisdom that does not cleanly apply to any one group.
If you want to know whether the long-legged creature in your basement eats other spiders, the key identifier is the web. Cellar spiders build irregular, tangled webs and hang upside-down in them. Harvestmen do not build webs and walk on surfaces. Crane flies have wings. Once you can tell the three apart, the behavioral claims sort themselves out: the one building the messy web is the confirmed spider predator.