Araneus Diadematus: The One-Year Life Cycle of the Cross Orb Weaver Spider
Often found calmly perched at the center of their sparkling, radial webs in gardens across Europe and North America, cross orb weavers (Araneus diademnatus) are among the most visually striking and kinetically graceful spider species frequently observed in urban settings. Other common names for the species include European garden spider, crowned orb weaver, and pumpkin spider.
Female cross orb weavers are easily identified by their robust abdomens, which can vary in color from mottled light beige to burnt orange to dark brown, but almost always feature two series of white dots that intersect perpendicularly to one another, forming the impression of a cross. These white spots are comprised of guanine, the same material responsible for the white appearance of some bird and bat droppings. Also notable are the spiders’ legs, each of which is comprised of seven distinct segments lined with small sensory hairs that give the spider an unshaven appearance.
Early Life (Late Fall Through Early Spring)
A cross orb weaver’s life begins among siblings. After being laid in the fall, hundreds of eggs nestle in stasis throughout winter within a squat, protective, egg-sac. These silk-based incubators are comprised of a short, cylindrical chamber capped by two disc-shaped plates. Egg-sacs are generally deposited under leaves or bark, or nestled in protected corners or eaves. As temperatures begin to rise in early spring, heat instigates the maturation process, and the cross orb weaver spiderlings emerge from their eggs. At this stage, the spiderlings usually appear bright yellow with the exception of a small, black area situated on on the hindmost portion of the abdomen.
Once they have emerged from their egg-sac, the young orb weavers begin to disperse gradually via a method known as ‘ballooning’. Still extremely lightweight, the spiderlings extrude thin strands of silk from their spinnerets to act as sails. These strands catch the breeze and lift the spiderlings into an arial commute that can range in distance from meters to kilometers. Each spiderling eventually lands in a strange, new environment in which it must begin the next stage of its life.
Middle Life (Summer)
Once a cross orb weaver completes the descent from its ballooning journey, its life as an independent, young-adult spider begins. Now alone, the young spider builds its trademark web. The webs created by cross orb weavers are highly geometrical, exhibit radial symmetry, and are built across a single plane, in contrast to the three dimensional tunnel webs and cob webs constructed by some spider species. Cross orb weavers anchor their webs to anything available, commonly enlisting the aid of twigs, posts, walls, bushes, and the ground to keep their webs in place. Webs constructed by cross orb weavers tend to have between 25 and 30 radial lines of silk which extend from the web’s center, or hub, to its perimeter.
Generally, cross orb weavers' webs are oriented perpendicular to the ground such that airborne insects are likely to fly into them when traveling laterally. Once an insect has been ensnared in its web, an orb weaver will rush to it and bite it immediately. The spider’s fangs inject a paralytic substance into the body of the insect, rendering it less able to defend itself and potentially injure the spider in the process. This same substance causes the interior of the insect to liquify so that it can be consumed by the spider after it has been wrapped in silk for storage. Depending on an orb weaver’s hunger level and the availability of prey, it may consume the liquified internal structures of a wrapped insect shortly after catching it, or store it for later consumption.
Cross orb weavers exhibit sexual dimorphism when mature, meaning male and female specimens differ noticeably in appearance. At maturity, males are smaller than females and have less rotund abdomens. While both male and female cross orb weavers build webs to catch prey, males cease to do so once they reach maturity, opting instead to wander in search of female orb weavers to inseminate. A male cross orb weaver may breed with multiple females, but a female orb weaver only needs to breed once. As is the case with many spider species, female orb weavers have a propensity to eat their mates, generally either before or after copulation, making the act a risky one for their male counterparts.
Once a female cross orb weaver has mated, she uses seminal vesicles to store the sperm she has acquired until she is ready to lay her eggs in the fall. Until then, she continues to sit at the hub of her web or hidden in nearby foliage awaiting the vibration of a ‘trip line’ of silk that signals the arrival of prey.
To ensure their continued efficacy, the webs of cross orb weavers are often consumed, recycled, and rebuilt by their inhabitants. When recycling their webs, orb weavers disassemble the structures, role them into conveniently consumable balls of silk, then eat them and reuse the silk proteins when producing subsequent webs.
End of Life (Late Summer/Early Fall)
As summer begins to wane and temperatures start to fall, female cross orb weavers prepare to lay their eggs, which can number in the hundreds. Once ready, soon-to-be mothers depart from their webs for the last time. Some individuals may choose to consume their web in order to replenish their silk-protein supply prior to creating their egg-sac. Once this is done, individuals often retreat to covered areas for several days.
Once an appropriately protected location is selected, the expectant orb weaver begins to construct her egg-sac. This process begins with the fabrication of a basal plate, which serves as one of two ‘caps’ to the cylindrical egg-sac. Silk produced by an individual’s spinnerets is molded by abdominal movements into an appropriately sized disc. This done, the spider crawls under the disc and continues to produce silk while spinning in circles in order to create a cylindrical wall beneath the first cap. After a brief rest, the spider begins to deposit her clutch of eggs into the silk cavity she has created.
Once her eggs have been successfully deposited, the orb weaver covers the open side of the egg-sac with silk, creating a second cap and sealing the chamber entirely. Next, she wraps silk around the entirety of the structure to fortify it as much as possible to prepare it to lay unguarded through winter. For the next few days, the new mother will remain close to her egg-sac in case any tears emerge that require repair. Several days after completing her egg-sac, the new mother stops moving for good.
Additional Information About Araneus Diademnatus
- Like other orb weaver species, diademnatus’ venom is not medically significant to humans.
- Due to the small size of their mouthparts and their preferred diet, orb weavers will rarely, if ever, bite humans.
- Adult male cross orb weavers are observed far less often than females because they are smaller, have shorter lifespans, and do not build or occupy webs once mature.
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