Spiders eat far less reliably than most animals, and their bodies are built for it. A spider can live well on a feast-and-famine diet that would quickly harm a mammal. How often a spider eats and how often it needs to eat are two very different numbers, and age matters more than species. Water is a separate need that food doesn’t cover.
How Often Spiders Eat in the Wild
Spiders in fields and gardens usually eat about one insect of a suitable size per day.1The Journal of Arachnology. Spider Predation: How and Why We Study It The striped lynx spider, a common crop spider, catches about one prey item on each rain-free day.2Journal of Applied Entomology. Insectivorous activities of spiders in United States field crops Rainy days often mean no meal at all. Even with plenty of insects around, a spider catches less than 1 in 100 of the possible prey near it each day.3Journal of Applied Entomology. Insectivorous activities of spiders in United States field crops Spiders are opportunists that wait for food to come to them rather than eating on a schedule.
Spider groups live very different lives, from web builders to roaming hunters, and their feeding patterns vary just as widely.4Oxford Academic. How Spiders Make a Living A web spider may get several insects in one night and then nothing for days, so an idle spider or an empty web is not a sign of a starving animal.
Meal size matters as much as frequency. A spider eats prey it can overpower, often close to its own size, so one large meal can stand in for several small ones.
A spider’s feeding record is also hard to read from the outside. One sitting in its web during the day is usually waiting rather than failing, because many web builders do most of their catching around dusk and at night. A tidy, empty-looking web isn’t evidence of hunger either: many orb weavers take down and rebuild their webs regularly, and a fresh web simply hasn’t had time to catch anything. Jumping spiders and wolf spiders have no web at all, so there is nothing to inspect, and body shape tells you more about how well they are eating than their surroundings do.
How Long a Spider Can Go Without Food
Spiders run on a low energy budget. Their metabolism, the rate a body burns energy, is 22 to 57 percent slower at rest than standard formulas predict for animals their size.5PubMed. Is spider resting metabolic rate more strongly associated with ecological guild or extreme habitat conditions? A resting spider therefore needs far less food than a similar-sized insect might. When food runs out, its energy use also falls gradually over time.6PubMed. Metabolic consequences of feeding and fasting on nutritionally different diets in the wolf spider Pardosa prativaga In one mountain tarantula, energy use dropped after about 3 weeks without food.7PubMed. Effects of diet and water supply on energy intake and water loss in a mygalomorph spider in a fluctuating environment of the central Andes
Fat does the rest. Spiders store fat as droplets in their gut, which feeds them through long periods without food.8PubMed Central. Digestive enzymes and sphingomyelinase D in spiders without venom (Uloboridae) Wolf spiders fed fattier prey built bigger fat stores and survived starvation longer than those fed leaner prey,9PubMed. Metabolic consequences of feeding and fasting on nutritionally different diets in the wolf spider Pardosa prativaga so what a spider ate before a fast affects how long it lasts. Cave spiders that overwinter with almost no food gradually use up their fat, sugar, and protein stores, much as many insects do in winter.10PubMed Central. Towards understanding partial adaptation to the subterranean habitat in the European cave spider, Meta menardi: An ecocytological approach11PubMed Central. Changes in the midgut diverticula epithelial cells of the European cave spider, Meta menardi, under controlled winter starvation They get through the winter until occasional prey turns up.12PubMed Central. Changes in the midgut diverticula epithelial cells of the European cave spider, Meta menardi, under controlled winter starvation
Fasting doesn’t disarm a spider. A large hunting spider fasted for 4 or 8 weeks lost body weight but kept its full venom supply.13PubMed. The influence of hunger and breeding temperature on the venom production of the spider Cupiennius salei (Araneae, Ctenidae)14PubMed. The influence of hunger and breeding temperature on the venom production of the spider Cupiennius salei (Araneae, Ctenidae)
In a pet or house spider, fasting looks quiet. The abdomen slowly shrinks and looks less plump, and the spider may sit still for long periods. A healthy adult with a full abdomen can safely go weeks between meals. A shriveled, wrinkled abdomen is a warning sign more often linked to lack of water.
Still, “a spider can survive months” isn’t a feeding plan. Surviving is different from thriving, since growth and egg-laying need steady food. Fat gets a spider through a gap, but it doesn’t replace the protein and other nutrients a spider takes from prey to grow and repair itself. A deeply depleted spider can’t rebuild its stores in a single meal, so recovery after a very long fast takes several meals over time.
Why Temperature Changes How Much a Spider Needs
A spider’s energy use rises as the temperature rises.15The Journal of Arachnology. Impacts of temperature, hunger and reproductive condition on metabolic rates of flower-dwelling crab spiders (Araneae: Thomisidae)16Journal of Arachnology. Impacts of temperature, hunger and reproductive condition on metabolic rates of flower-dwelling crab spiders (Araneae: Thomisidae) In crab spiders, energy use roughly doubled with each 10°C rise between 10 and 40°C.17The Journal of Arachnology. Impacts of temperature, hunger and reproductive condition on metabolic rates of flower-dwelling crab spiders (Araneae: Thomisidae) A spider kept warm needs food more often than one kept cool. Some spiders cut their energy use especially sharply in the cold, which helps them save energy through bad weather.18The Journal of Arachnology. Impacts of temperature, hunger and reproductive condition on metabolic rates of flower-dwelling crab spiders (Araneae: Thomisidae) Spiders in a cool garage or a winter garden can go much longer between meals.
A warm spider also drains its fat much faster during a fast, so the “weeks without food” figure shrinks as the temperature rises. Very high heat stresses a spider, and it isn’t a way to get more growth out of it.
Outdoor spiders follow the same logic through the year. They eat most in late summer when insects are plentiful, and in autumn and winter many slow down and eat little or nothing.
For pet keepers, a cooler enclosure often brings a smaller appetite that isn’t cause for alarm. Don’t overheat a spider to make it eat.
Young Spiders Need Food More Often
Steady food decides whether spiderlings survive. Brown widow spiderlings fed every week mostly survived, with about 60 percent reaching adulthood.19The Journal of Arachnology. Growth, development, and survival in the brown widow spider, Latrodectus geometricus, under different feeding regimes Those fed only every three weeks died at much higher rates.20The Journal of Arachnology. Growth, development, and survival in the brown widow spider, Latrodectus geometricus, under different feeding regimes Growing up also takes a lot of molting, which is shedding the old skin to grow. Female brown widows molted 8 to 9 times and took about 170 days to reach full size, while males molted about 4 times and took about 100 days.21The Journal of Arachnology. Growth, development, and survival in the brown widow spider, Latrodectus geometricus, under different feeding regimes Females need a longer stretch of good feeding to grow up. Adult females producing eggs need more food than males or resting adults. Spiderlings lack an adult’s stored fat, so a gap an adult would barely notice can be dangerous for them.
More food isn’t always better. Young spiders fed very heavily grew fastest but were more likely to die while molting.22PubMed. Growth and development rates in a riparian spider are altered by asynchrony between the timing and amount of a resource subsidy Spiders whose growth was slowed early on could fully catch up later on a steady diet.23PubMed. Growth and development rates in a riparian spider are altered by asynchrony between the timing and amount of a resource subsidy
Molting is risky because the spider sheds its whole outer skin and is soft and helpless for a while. Spiders often refuse food for days before and after. Live prey left in the enclosure can injure a freshly molted spider, so wait until the new skin hardens before offering food.
How Often to Feed a Pet Spider
Age is the best guide. Weekly feeding kept most young widow spiders alive to adulthood, while a meal every three weeks did not,24The Journal of Arachnology. Growth, development, and survival in the brown widow spider, Latrodectus geometricus, under different feeding regimes so feed spiderlings at least once a week, and more often if they eat eagerly. Adult spiders can safely go weeks between meals,25PubMed. Metabolic consequences of feeding and fasting on nutritionally different diets in the wolf spider Pardosa prativaga26PubMed Central. Digestive enzymes and sphingomyelinase D in spiders without venom (Uloboridae) so a meal every one to two weeks is generally enough for most adults. Fast-growing or egg-carrying spiders do better with more frequent meals. A half-grown juvenile can be fed about weekly, and an adult that has stopped growing needs food only to maintain itself.
Prey should be roughly no larger than the spider’s body. One appropriately sized cricket or fly is usually a full meal, while too-large prey can fight back and injure the spider.
The abdomen is a better guide than the calendar. A plump, round abdomen means the spider is well fed and can skip meals, and a noticeably slim one means it is time to offer food. Refusing food with a plump abdomen is normal, not illness. When a spider turns down a meal, remove the prey and try again in a few days rather than forcing the matter. Refusal that lasts a long time in a slim spider, or that comes with changes like curled legs, is a reason to check temperature and water before anything else.
Take out live prey not eaten within a day. Crickets left in can nibble on a resting or molting spider, and leftover remains invite mold and mites.
Spiders Need Water as Well as Food
Orb web spiders cannot get enough water from prey alone.27Ethology. Water as an Essential Resource: Orb Web Spiders Cannot Balance Their Water Budget by Prey Alone Spiders kept without water drank much more once it was offered, whether or not they had been fed.28Ethology. Water as an Essential Resource: Orb Web Spiders Cannot Balance Their Water Budget by Prey Alone They may also need fresh water to process the food they eat.29Ethology. Water as an Essential Resource: Orb Web Spiders Cannot Balance Their Water Budget by Prey Alone A pet spider should always have access to water, such as a shallow dish or droplets on the enclosure wall.
Thirst can develop even in a well-fed spider. The abdomen shrinks with both hunger and thirst, so a shriveled spider can look hungry when it actually needs a drink. Check water first.
Outdoors, spiders sip dew and raindrops from webs and leaves. At home, a shallow dish with a low rim, or one filled with pebbles, lets a spider drink while greatly lowering the chance that a small spider falls in and drowns. Refresh it regularly, since stale water can grow bacteria and mold in a warm enclosure. Light misting suits species that drink droplets from silk or walls, but keep it light so the enclosure doesn’t stay soaking wet.
How a Hungry Spider Behaves
Hunger changes behavior. Hungry wolf spiders travel further than well-fed ones, moving more often.30PubMed. The effects of hunger on locomotory behaviour in two species of wolf spider (Araneae, Lycosidae) Starving widow spiders spin more silk for catching prey and less for protecting themselves.31PubMed Central. Starving infecund widow spiders maintain sexual attractiveness and trade off safety for enhanced prey capture A spider that wanders a lot or rebuilds its web constantly may be hungry, while a still, hidden spider with a full abdomen is usually just resting.
A roaming spider may be searching for a mate or a new site. A spider rebuilding its web night after night is likely catching little, though ordinary upkeep also leads many orb weavers to rebuild often. The best read combines several signs: a slim abdomen, restless movement, and a quick response to prey.
A hungry spider pounces quickly when prey moves near it. A spider about to molt often stops eating and hides, may look dull or dark, and may seal itself in silk.