Orb-weaving spiders feed primarily on small flying insects, with flies and wasps making up the bulk of their meals. But the full picture of their diet is more varied and stranger than that summary suggests. Research has shown that pollen can account for a meaningful share of what juvenile orb weavers consume, and at the extreme end, large tropical species have been documented catching and eating bats. How orb weavers hunt is as interesting as what they eat, because their webs are not just passive traps but finely tuned tools shaped by evolution to exploit the sensory systems of their prey.
What Shows Up on the Menu
The prey that lands in an orb weaver’s web is largely determined by what is flying through the air in its habitat. Studies consistently find that orb webs intercept mostly small, lightweight insects, reflecting whatever insect families are most common in the area.1PubMed. Influence of web traits, height, and daily periods of exposition on prey captured by orb-weaver spiders Flies (Diptera) and small wasps or bees (Hymenoptera) tend to dominate the catch. Moths, beetles, and other winged insects also get trapped, but the bread and butter for most orb weavers is whatever tiny flying insect blunders into the silk.
This is partly a function of physics. An orb web is an aerial net, and like any net, it catches what fits its mesh. Small insects lack the momentum to punch through the silk, and they lack the body mass to rip free once the glue threads make contact. Larger insects, by contrast, can sometimes tear through or escape before the spider arrives. So while an orb weaver will happily eat a large moth or beetle if one gets stuck, the typical meal is something small enough to be reliably held by the web.
Pollen as a Genuine Food Source
One of the more surprising findings in orb weaver biology is that these spiders eat pollen, and not just incidentally. When juvenile orb weavers emerge in spring, insect prey can be scarce, but airborne pollen and fungal spores are abundant. Those particles stick to the same glue-coated silk threads that catch insects, and when the spider recycles its web by eating the silk (a common orb weaver behavior), it ingests the pollen along with it.
This is not trivial nutrition. Research on the European garden spider found that pollen caught on sticky silk doubled the life expectancy of spiderlings compared to those that received no food at all, and it changed their web-spinning behavior so they rebuilt webs more frequently than fasting controls.2PubMed. Pollen feeding in an orb-weaving spider A later study quantified the contribution more precisely, finding that about 25% of juvenile orb weavers’ diet consisted of pollen, with the remaining 75% coming from flying insects, mainly small flies and wasps.3PubMed Central. Herbivory in spiders: the importance of pollen for orb-weavers Spiders that ate both pollen and flies achieved the best nutritional outcomes, with the combination delivering all essential nutrients. For young orb weavers, pollen is not a last resort but a real and regular part of the diet.
How the Web Catches and Holds Prey
An orb web is often described as a passive trap, but the engineering behind it is anything but simple. The capture spiral, the sticky portion of the web, is coated with tiny glue droplets. Each droplet has a glycoprotein core that creates adhesion on contact. When an insect hits the web, its struggle activates multiple droplets simultaneously, and a “suspension bridge” effect forms between them. This structure sums the adhesive force of many droplets while dissipating the kinetic energy of the struggling prey, making escape progressively harder the more the insect thrashes.4PubMed Central. Correlated evolution between orb weaver glue droplets and supporting fibres maintains their distinct biomechanical roles in adhesion
Not all orb weaver glue is the same. Some species have evolved specialized adhesives tuned to their particular prey. The moth-catching spider Cyrtarachne akirai, for example, produces glue droplets roughly eight times larger than those of typical orb weavers, making its threads about eight times more adhesive on a surface. But the really clever adaptation is in viscosity: this spider’s glue is about a thousand times less viscous than standard orb weaver glue at peak adhesive humidity, which lets it spread rapidly across moth wing scales before the moth can pull free.5PubMed Central. Supersaturation with water explains the unusual adhesion of aggregate glue in the webs of the moth-specialist spider, Cyrtarachne akirai The glue essentially races the prey’s escape attempt.
Web Decorations That Lure Insects
Many orb weavers add conspicuous patterns of extra silk to their webs, known as stabilimenta or web decorations. These bright white structures reflect ultraviolet light, and for decades researchers debated their function. One leading explanation, now well supported, is that the decorations actively attract prey by exploiting insects’ UV-sensitive vision.
Lab experiments with juvenile Argiope spiders showed that fruit flies flew toward webs with UV-reflecting disc-shaped decorations significantly more often than toward undecorated webs when both were lit with UV-inclusive white light.6Animal Behaviour. Prey attraction as a possible function of discoid stabilimenta of juvenile orb-spinning spiders Field studies support the same conclusion: spiders that decorated their webs more frequently intercepted more prey and grew faster.7PubMed Central. Spiders that decorate their webs at higher frequency intercept more prey and grow faster
The effect is not uniform across all insects, though. In field experiments with Argiope keyserlingi, decorated webs caught more houseflies, blowflies, stingless bees, honeybees, and vespid wasps, all of which have visual receptors sensitive to blue and UV light. Interestingly, ichneumonid wasps, which are parasites that pose a threat to the spider, were caught less frequently in decorated webs.8Biological Journal of the Linnean Society. Why cross the web: decoration spectral properties and prey capture in an orb spider (Argiope keyserlingi) web Whether UV alone, blue light alone, or both together serve as the primary attractant remains an open question, but the general principle is clear: some orb weavers have evolved silk structures that function as visual lures.
Day Feeders and Night Feeders
Whether an orb weaver hunts during the day or at night shapes what it catches. A comparison of two Australian orb weavers illustrates the pattern neatly. The diurnal species Nephila plumipes maintains a relatively permanent web and catches most of its prey during daylight hours, primarily Hymenoptera (bees and wasps) that are active during the day. The nocturnal species Eriophora transmarina builds a fresh web every evening and dismantles it at dawn, catching mostly Lepidoptera (moths) that fly at night.9Australian Journal of Ecology. Foraging strategies of Eriophora transmarina and Nephila plumipes (Araneae: Araneoidea): Nocturnal and diurnal orb‐weaving spiders
The nightly web-building strategy might seem wasteful, but it serves nocturnal species well. A freshly spun web has maximum stickiness, and rebuilding each night lets the spider choose the best location based on current conditions. It also means the web is invisible to diurnal predators like birds during daylight hours. For day-active species, a permanent web avoids the energy cost of nightly reconstruction but means living with silk that gradually loses its adhesive properties and accumulates damage.
How Orb Weavers Digest Their Prey
Spiders cannot chew. They have no teeth and no ability to mechanically break down solid food. Instead, orb weavers use a process called extra-oral digestion: they inject or regurgitate digestive fluids into or onto the prey’s body, liquefying the tissues externally, then suck up the resulting nutrient soup.10PubMed Central. Characterisation of protein families in spider digestive fluids and their role in extra-oral digestion
Venom plays the first role, immobilizing the prey so the spider can wrap it in silk and begin the slower process of digestion. Orb weaver venoms contain compounds called argiotoxins that block neuromuscular transmission in insects, causing reversible paralysis at very low concentrations.11Biochemical and Biophysical Research Communications. Structures and biological activities of three synaptic antagonists from orb weaver spider venom Once the prey is subdued, the spider’s digestive fluids go to work. These fluids are rich in trypsin-like enzymes, the same class of protein-digesting enzymes found in the human gut, though the spider is applying them externally rather than internally.10PubMed Central. Characterisation of protein families in spider digestive fluids and their role in extra-oral digestion What the spider eventually discards is a dried husk, a hollow exoskeleton with the nutritious interior completely dissolved and consumed.
When Prey Fights Back
Not every insect that hits an orb web ends up as dinner. Moths, in particular, are famously good at escaping. Their wings and bodies are covered in loose scales that function as a sacrificial layer: when the scales contact the web’s sticky threads, they flake off, leaving the adhesive coated in detached scales while the moth pulls away with bare wing membrane underneath.12PubMed Central. Behavior and Bioadhesives: How Bolas Spiders, Mastophora hutchinsoni, Catch Moths The result is that moths escape from standard orb webs far more often than comparably sized insects without scales.
Some orb weavers have co-evolved solutions to this problem. The moth-specialist Cyrtarachne akirai, mentioned earlier for its low-viscosity glue, takes advantage of the scales rather than fighting them. Its rapidly spreading adhesive actually uses detached scales as additional surface area for bonding, turning the moth’s own defense into an anchoring mechanism.13PubMed Central. The moth specialist spider Cyrtarachne akirai uses prey scales to increase adhesion This is one of the more elegant evolutionary arms races in arachnid biology: the prey evolves disposable armor, and the predator evolves glue that weaponizes that same armor.
Bolas Spiders and Chemical Hunting
The most radically different hunting strategy among orb weaver relatives belongs to the bolas spiders in the genus Mastophora. These spiders have abandoned the web entirely. Instead, they dangle a single silk thread tipped with a large sticky globule and swing it at passing moths like a fishing lure. But the real trick is not mechanical; it is chemical.
Bolas spiders produce volatile compounds that mimic the sex pheromones of their moth prey. Analysis of emissions from hunting female Mastophora cornigera identified three specific moth sex pheromone components, chemicals that in the wild are released by female moths to attract males for mating.14PubMed. Chemical mimicry: bolas spiders emit components of moth prey species sex pheromones Male moths following the scent trail arrive expecting a mate and instead encounter a sticky ball of silk swung by a spider.
The specificity is remarkable. In a study tracking over 490 prey captures by Mastophora hutchinsoni, only male moths were caught, and just two species of noctuid moths accounted for 93% of the total catch.15PubMed. Ecology of a bolas spider, Mastophora hutchinsoni: phenology, hunting tactics, and evidence for aggressive chemical mimicry From a large available moth community, the spider targets an extremely narrow slice, pulling in only those species whose pheromone blends it can convincingly fake. This is about as far from the generalist strategy of a typical orb web as a spider can get while still being classified in the same broad group.
When the Catch Gets Big
Orb weavers are not limited to insects. Large tropical species, particularly golden silk orb weavers in the genus Nephila and the genus Eriophora, build webs that can reach 1.5 meters in diameter, strong enough to occasionally catch vertebrate prey. Documented cases include bats that have become entangled in these massive webs. In some cases the bats died from exhaustion, dehydration, or overheating while trapped, but in many other instances spiders were observed actively attacking, killing, and feeding on the captured bats.16PubMed Central. Bat predation by spiders
Bat predation is clearly not a dietary staple. It is rare enough to make headlines among researchers when documented. But it does demonstrate the upper bound of what orb weaver silk and venom can handle, and it challenges the assumption that spiders are strictly small-invertebrate predators. The webs of the largest orb weavers are genuinely strong structures, reinforced by thicker dragline silk and spanning wide gaps between vegetation. An unlucky small bat flying through such a web at night faces the same physics as a large moth: once the glue makes contact and momentum is absorbed, escape requires more force than the animal can generate.
Thieves in the Web
Orb weavers face a dietary problem that has nothing to do with catching prey and everything to do with keeping it. Kleptoparasitic spiders, tiny species in the family Theridiidae, live as permanent residents on the webs of larger orb weavers and steal food directly from their hosts. These freeloaders position themselves in peripheral areas of the web and dart in to feed on small prey items that the host spider ignores or does not notice.
Web size has long been the best predictor of how many kleptoparasites a web will host: bigger webs attract more thieves. But a recent study of golden orb weavers in Madagascar found that wind exposure had an even stronger effect. Webs that swayed more in the wind harbored fewer kleptoparasites, even after controlling for web size.17The Science of Nature. Gone with the wind: wind-induced web movement reduces kleptoparasite abundance in a golden orbweaver spider The constant motion of a wind-buffeted web apparently makes it a less hospitable platform for the smaller spiders that rely on stable footing to operate. For the orb weaver, an exposed, breezy web site may mean catching slightly less prey due to web movement but losing less of what it does catch to theft.
Urban Light and Shifting Diets
Artificial light at night is reshaping the foraging landscape for nocturnal orb weavers. Streetlights and building lights attract enormous numbers of flying insects, creating concentrated prey patches that don’t exist in unlit habitats. Field experiments found that webs placed near LED lights captured significantly more prey than webs in dark control areas.18Ethology. Guiding lights: Foraging responses of juvenile nocturnal orb‐web spiders to the presence of artificial light at night
The downstream effects are measurable. Researchers have observed increases in body size, reproductive output, and population density among orb web spiders in well-lit urban environments compared to nearby dark sites. The foraging benefit of abundant light-attracted prey appears to offset whatever physiological costs come with constant exposure to artificial light. For a nocturnal orb weaver, a streetlamp is essentially a buffet sign: it concentrates the flying insects the spider already eats into a small area, making every web spin dramatically more productive. This partly explains why certain orb weaver species thrive in cities even as their rural populations face pressure from habitat loss and declining insect numbers. The urban environment, for all its strangeness from a spider’s perspective, provides dependable, concentrated food.