A spider trapped in a typical glass jar with the lid screwed tight will usually die within a few days to a couple of weeks, depending on the species, the size of the jar, and whether it has any access to moisture. The limiting factor is rarely oxygen or starvation; it is almost always dehydration. A small house spider in a dry, sealed mason jar at room temperature might last three to ten days, while a larger, hardier species with some moisture available could persist for several weeks or even longer. The answer shifts dramatically once you change even one variable, which is why a simple number of days does not capture the full picture.
What Kills a Jarred Spider First
Three things can kill a spider in a sealed container: running out of breathable air, drying out, or starving. Of those three threats, dehydration is almost always the one that gets there first. Spiders are small, and their respiratory systems are efficient enough that the oxygen inside a typical jar will last much longer than their water reserves. Starvation, meanwhile, is a problem that unfolds over weeks or months for most species, not days. So when someone finds a dead spider in a jar they sealed up and forgot about, the spider almost certainly died of thirst.
This priority order matters because it tells you what to focus on if you want to keep a spider alive in a container for any length of time. A damp cotton ball or a small dish of water will do far more for survival than poking air holes in the lid, though ventilation helps for a different reason (it prevents the buildup of carbon dioxide and regulates humidity).
How Long the Air Actually Lasts
Spiders breathe using a combination of book lungs and tracheae, depending on the species. Both systems are passive and low-demand compared to a warm-blooded animal. A spider’s metabolic rate is a fraction of what a mammal of the same weight would burn, which means it consumes oxygen slowly. In a standard pint-sized mason jar with roughly 470 milliliters of air, a small spider would take a long time to deplete the oxygen to dangerous levels. For most common household spiders, oxygen in a sealed jar of that size is not the bottleneck for at least several days, and often much longer.
That said, it is not just about oxygen dropping. Carbon dioxide builds up as the spider respires, and rising CO₂ can stress spiders before the oxygen level becomes truly critical. Research on the linyphiid spider Hylyphantes graminicola found that elevated carbon dioxide concentrations significantly decreased the spider’s survival rate, even when other factors like nutrition and development were unaffected.1PubMed. Elevated CO(2) concentration affects survival, but not development, reproduction, or predation of the predator Hylyphantes graminicola (Araneae: Linyphiidae) In a sealed jar, the CO₂ concentration would climb gradually as the spider breathes, creating a slowly worsening environment even if plenty of oxygen technically remains.
Some spiders handle low-oxygen conditions better than others. A study on the intertidal jumping spider Desis marina, which builds silk nests in barnacle shells that get submerged by the tide, found that spiders in nests flooded with seawater for an hour continued to respire and experienced only minimal hypoxia inside their silk retreats.2Journal of Zoology. Behavioural and physiological adaptations of a jumping spider to a marine environment That is an extreme example of a spider adapted to tolerate enclosed, low-oxygen conditions, and it would be a mistake to assume a common cellar spider or cobweb spider could handle the same. But it illustrates that spiders as a group are not especially oxygen-hungry creatures.
Dehydration Is the Real Deadline
Water loss is what sets the clock on a jarred spider’s life. Spiders lose moisture through their cuticle (their outer body surface) and through respiration. The rate at which they dry out depends heavily on the humidity inside the container and the spider’s own body size and surface-area-to-volume ratio. A tiny spider dries out faster than a large one, simply because it has relatively more surface area for its body mass.
Research on the wolf spider Schizocosa ocreata showed that spiders survived significantly longer when kept at humidity levels of 50% or higher. Below that threshold, survival dropped off sharply.3Canadian Journal of Zoology. Dehydration resistance and tolerance in the brush-legged wolf spider (Schizocosa ocreata): a comparison of survivorship, critical body water content, and water-loss rates between sexes The same study found that female wolf spiders outlasted males under dry conditions, showing lower rates of water loss and greater overall dehydration tolerance. Sex differences in water management are common across spider species and partly explain why survival times can vary even among members of the same species in identical conditions.
In a sealed glass jar sitting on a kitchen counter, the humidity inside will depend on the ambient room conditions and whether the jar was dry when you closed it. A typical home interior sits around 30 to 50% relative humidity, and a sealed jar will equilibrate somewhere in that range. Without a water source, a small spider in that environment might have three to seven days before dehydration becomes lethal. A larger spider with a better surface-area ratio could stretch that to two weeks or more. Adding a moist piece of sponge, a damp paper towel, or a shallow water dish changes the equation entirely and can extend survival dramatically.
How Long Spiders Can Go Without Food
Spiders are remarkably good at not eating. Their metabolic strategy is built around feast-and-famine cycles. In the wild, prey capture is unpredictable, and many spiders routinely go days or weeks between meals even outside of any captive situation. When food is unavailable, spiders dial back their energy expenditure and shift to burning stored lipids, much like a hibernating bear draws on fat reserves.4Comparative Physiology of Fasting, Starvation, and Food Limitation. Metabolic Transitions During Feast and Famine in Spiders
As a spider fasts, its oxygen consumption and carbon dioxide output both decrease gradually, reflecting the lower metabolic rate.5Journal of Insect Physiology. Metabolic consequences of feeding and fasting on nutritionally different diets in the wolf spider Pardosa prativaga Interestingly, spiders that had been eating lipid-rich prey before a fast survived longer during starvation than those that had been eating protein-rich prey, because they had larger fat reserves to draw from. This makes intuitive sense: fat is a more energy-dense fuel source, and a spider that starts a fast with full lipid stores has more runway.
Another survival trick during fasting is that spiders defend their body mass by increasing their relative body water content, essentially replacing some of the mass lost from burned fat stores with water.4Comparative Physiology of Fasting, Starvation, and Food Limitation. Metabolic Transitions During Feast and Famine in Spiders This is physiologically clever, but it creates an ironic vulnerability in a jar: the spider’s starvation strategy depends on having water available to maintain body mass. In a dry jar, the spider cannot use its normal fasting playbook because it is losing water faster than it can compensate. So even though a well-hydrated spider could technically survive weeks or months without food, dehydration in a sealed jar cuts that timeline short.
For common house spiders with access to water but no food, survival on the order of one to three months is plausible, and some larger species can go considerably longer. Tarantula keepers occasionally report their spiders refusing food for months at a stretch with no ill effects, which tracks with the extreme starvation tolerance documented across the spider order.
Species Size and Lifespan Make a Huge Difference
Not all spiders are created equal when it comes to surviving captivity. A tiny money spider with a body length of a few millimeters is working with a fundamentally different set of reserves than a tarantula the size of your hand. Body size affects water-loss rate, fat storage capacity, and baseline metabolic demand, all of which compound to create enormous variation in how long different species can survive in a jar.
Tarantulas are the extreme end of the spectrum. Female tarantulas of the species Brachypelma albopilosa can live upward of 20 years in captivity, while males of the same species survive only one to two years after reaching sexual maturity.6PubMed Central. Increased ROS production: a component of the longevity equation in the male mygalomorph, Brachypelma albopilosa That dramatic sex-based difference in lifespan is driven partly by oxidative stress: males produce more damaging reactive oxygen species and have weaker antioxidant defenses after maturing. For the jar question, what this means practically is that a mature female tarantula with adequate humidity and ventilation could survive in a large, well-maintained enclosure for years, while a mature male tarantula is on a tighter biological clock regardless of conditions.
At the other end, the small orb weavers, cellar spiders, and cobweb spiders commonly found in homes have natural lifespans of roughly one to two years. Their reserves are proportionally smaller. A common cellar spider (Pholcus phalangioides) sealed in a dry jar without food or water would likely be dead within a week or two. The same spider in a jar with a damp cotton ball and the occasional fruit fly could potentially live for months.
Temperature and the Metabolic Dial
Because spiders are ectotherms, their metabolic rate tracks the ambient temperature. A warmer jar means a faster metabolism, which means faster oxygen consumption, faster water loss, and faster depletion of energy reserves. A cooler jar slows everything down. This is not a minor effect; it can easily double or halve the survival time depending on whether the jar is sitting in a warm kitchen or a cool garage.
Research on overwintering spiderlings of Argiope bruennichi showed that survival probability dropped by roughly 20% over the winter period, and their lipid content fell by about 28%, with no significant difference between groups kept at warmer versus cooler winter regimes.7PubMed Central. Winter Temperature Affects Fatty Acid Composition and Gene Expression, but Not Fat Content and Survival in a Northern Population of a Range-Expanding Spider However, the spiderlings exposed to warmer winter temperatures showed signs of a more pronounced physiological stress response, including changes in fatty acid composition and gene expression that suggested metabolic costs. The implication is that even when short-term survival numbers look similar, warmer conditions impose hidden costs that may reduce a spider’s fitness and longevity after the stress period ends.
Many spider species also have the ability to enter a dormancy state during unfavorable conditions. Various forms of diapause, triggered by temperature or day length, allow spiders to suppress their metabolism and conserve resources. During diapause, oxygen consumption drops measurably, and some species can lower their supercooling points in response to falling temperatures, essentially recalibrating their physiology for extended periods of minimal activity.8Zeitschrift für Angewandte Entomologie. Winter ecology of spiders (Araneida) A spider that enters dormancy in a cool, humid jar could outlast one that remains active in a warm, dry jar by a wide margin.
Sealed Versus Ventilated Containers
The distinction between a completely sealed jar and one with ventilation holes is important, and it affects more than just air supply. A sealed jar is a closed system: the spider’s exhaled CO₂ accumulates, humidity can only go down as the spider’s body water evaporates into the air and is not replenished, and temperature can spike if the jar sits in sunlight. A ventilated jar, by contrast, allows gas exchange with the outside air, keeps CO₂ from building up, and lets ambient humidity reach the spider.
In practice, a few small holes punched in a metal jar lid, or a piece of mesh fabric secured over the opening, transforms the survival math. The oxygen and CO₂ problems essentially vanish. Humidity inside the jar will track the room’s humidity rather than slowly declining. The spider still needs water and eventually food, but you have removed the two atmospheric threats and bought considerably more time.
If someone has accidentally trapped a spider under a glass on a counter, the gap between the glass rim and a flat surface usually allows enough air exchange that suffocation is not an immediate concern. The spider in that scenario is more likely to die of thirst over a couple of days than to suffocate. Still, the longer you leave it, the worse the conditions get.
Keeping a Spider Alive in a Jar Temporarily
People sometimes want to keep a spider they have caught for observation, identification, or relocation. If you plan to hold a spider in a jar for more than a few hours, a handful of simple steps will make the difference between finding a live spider and finding a shriveled corpse.
- Ventilation: Poke several small holes in the lid or use a piece of fine mesh instead. This prevents CO₂ buildup and allows humidity exchange.
- Moisture: Place a small damp cotton ball or a piece of wet paper towel in the jar. This is the single most important thing you can do. Spiders drink water droplets from surfaces and will use a moist substrate to rehydrate.
- Shade and temperature: Keep the jar out of direct sunlight and away from heat sources. A jar in the sun can become an oven in minutes, and elevated temperatures accelerate water loss and metabolic burn.
- Size matters: A bigger container gives the spider more air volume and more space to move, which reduces stress. A large plastic deli cup or a quart jar is better than a shot glass.
- Food (if longer than a few days): A small live insect like a fruit fly or a tiny cricket gives the spider both nutrition and moisture from the prey’s body. Many spiders will eat within a day of being captured if they are not too stressed.
With ventilation, moisture, and a cool location, most common spider species can survive in a jar for weeks. Without those provisions, the window shrinks to days.
Why Web-Building Spiders Do Worse in Small Spaces
Spiders that rely on webs for prey capture tend to struggle more in small containers than active hunters like jumping spiders or wolf spiders. A web-building spider in a jar will try to construct a web, but the confined space produces a cramped, nonfunctional structure that wastes silk (and therefore protein) without catching anything. The spider may rebuild repeatedly, burning through energy reserves faster than a hunter that simply sits and waits.
Active hunters, by contrast, often adapt reasonably well to a small space. Jumping spiders in particular are known for tolerating captivity and will readily explore a container, drink water droplets, and pounce on small prey items introduced into the space. Their hunting style does not depend on architecture, so confinement does not impose the same metabolic tax.
This behavioral difference means that a cobweb spider and a jumping spider of similar size, placed in identical jars with the same provisions, may have noticeably different survival timelines. The cobweb spider expends silk and energy on futile web-building; the jumping spider conserves both by sitting tight.
What Happens When a Spider Dies in a Sealed Jar
If curiosity brought you to this question because you found a dead spider in a jar, the cause of death is almost certainly dehydration unless the jar was extremely small and airtight, in which case CO₂ accumulation might have contributed. A dehydrated spider typically curls its legs inward because spider legs extend using hydraulic pressure from body fluid, not muscles. When the body runs out of fluid, the hydraulic system fails and the legs retract into the familiar “death curl.” A spider that died of starvation over a longer period with water available would look similar but would often have a noticeably shrunken abdomen, since the abdomen is where lipid reserves and much of the body’s water are stored.
If the jar has been sealed for a very long time, decomposition is minimal because the enclosed space limits the microorganisms available to break down the body. Spiders left in sealed jars sometimes desiccate into surprisingly well-preserved husks that can last for months or years, which is incidentally the principle behind certain museum specimen preservation methods, though those use ethanol rather than air.