Araneidae  

Spiders hatch from eggs. The hatchlings look more or less like grown-up spiders, though sometimes their colors change as they age. To grow they have to shed their exoskeleton. They do this many times during their lives.

The family Araneidae (orbweavers) includes more than 3000 described species; nearly 7% of all known spider species are araneids (Platnick 2013). In North America north of Mexico, there are around 161 known araneid species placed in 31 genera. Of the seven families of spiders that spin flat orb webs, the Araneidae has the most species. Many araneids are fairly large and colorful and the family includes a number of familiar spiders. Most araneids have roundish bodies and fairly short, relatively thick legs. In some species, there is strong sexual size dimorphism, with males much smaller than females. (Bradley 2013) Like most spiders, araneids have eight eyes.

Many araneid species have distinctive dark patches and light spots on the underside of the abdomen. These are especially conspicuous when viewed with a flashlight or headlamp at night. For example, the larger Araneus species and all Neoscona have a large rectangular black area with white or yellowish spots or comma-shaped marks at each corner. Argiope have a black patch with many small pale spots. Other genera, such as Aculepeira and Metepeira, have a black patch with white lines. These markings are often helpful in recognizing genera, but are rarely sufficient to identify particular species. (Bradley 2013)

Orbweavers have relatively poor vision and sense their prey by their vibrations. When a potential food item hits a web, the spider rushes over and quickly wraps it in a cocoon of silk, biting and paralyzing it once it is sufficiently immobilized. The wrapped prey may be cut out of the web and brought back to the web hub or to a retreat, where the spider begins feeding. Unlike many spiders, araneids chew their food (Levi 2005). Sometimes a wrapped prey item is kept for some time before being consumed. Although most araneids build vertical orb webs, Mecynogea build a fine-meshed horizontal web and a few species spin reduced webs or capture prey in other ways (e.g., Mastophora bolas spiders, which attract male moths with scent and catch them by swinging a thread with an attached sticky ball at them as they approach). Nocturnal orbweavers may take down their webs in the morning and eat them, then re-build them in the evening; diurnal orbweavers rebuild their webs in the morning. (Levi 2005; Bradley 2013)

Most larger araneids in North America mature in summer and fall, but others mature in spring. Typical life span is one to two years. Dew-covered webs are easily located by walking toward the sun in the morning. Araneids are collected by beating branches or sweeping vegetation with a net. The American araneid fauna has been revised and illustrated by H.W. Levi and his students (1968 to present) and Dondale et al. (2003) have illustrated additional species. (Levi 2005)

The araneid Araneus cavaticus is perhaps the most famous spider in literature (at least in the English language), since this species was the model for Charlotte in Charlotte's Web by the 20th century American author E.B. White.

(Levi 2005; Bradley 2013)

Granules prevent slippage: orb-weaver spiders
 

Glue droplets on orb-weaver spider webs resist slippage through adhesion, elongation under load, and force transfer due to granules.

 
  "Sticky viscous prey capture threads form the spiral elements of  spider orb-webs and are responsible for retaining insects that  strike a web. These threads are formed of regularly spaced aqueous  droplets that surround a pair of supporting axial fibers. When  a thread is flattened on a microscope slide a small, opaque granule  can usually be seen within each droplet. These granules have  been thought to be the glycoprotein glue that imparts thread adhesion.  Both independent contrast and standard regressions showed  that granule size is directly related to droplet volume and  indicated that granule volume is about 15% of droplet volume. We  attempted to find support for the hypothesized adhesive role of  granules by establishing an association between the contact surface  area and volume of these granules and the stickiness of the  viscous threads of 16 species in the context of a six-variable model  that describes thread stickiness. However, we found that granule  size made either an insignificant or a small negative contribution  to thread stickiness. Consequently, we hypothesize that  granules serve to anchor larger, surrounding layers of transparent  glycoprotein glue to the axial fibers of the thread, thereby  equipping droplets to resist slippage on the axial fibers as  these droplets generate adhesion, elongate under a load, and  transfer force to the axial fibers." (Opell & Hendricks 2010:339)
  Learn more about this functional adaptation.

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