What is Ontogeny?

Ontogeny describes how a behavior changes over the course of the animal’s lifetime.  It often examines the roles of social and environmental conditions in the development of behavior, and how the underlying machinery of behavior—such as gene expression, neurocircuitry, hormonal pathways, and morphology—change in response to varying environmental conditions.    

Web Building is Innate 

The basic motor patterns involved in construction of the orb web are largely stereotypical within phylogenetic clades of orb weaving spider families, resulting in species-specific differences in web architecture (Blackledge, et. al, 2011).  This suggests that there is a genetic basis for web-building behavior in these spiders, or rather that the behavior is innate.  Spider hatchlings raised in the absence of adults were observed to initially lay silk in no clear structure, but after one month, the young spiders constructed webs showing features characteristic of the adult webs of their species (Witt, et al, 1972), supporting the hypothesis that the basic web building behavior is internal to the spider and does not have to be learned. 

Changes in the Orb Web as Spiders Age

As a spider develops from juvenile to adult, the web that it builds grows in overall size and the size of the mesh becomes wider with greater spacing among threads.  While the size of the web is correlated to a spider’s weight, the regularity in thread spacing is related to spider maturity.  Because the weight of female spiders does not change after they reach maturity and produce eggs, the size of the web no longer needs to change to hold a greater mass.  With further aging, the web texture becomes increasingly coarse with irregular spacing until the spider’s final molt (Witt, et. al, 1972). 

There is no evidence that silk production varies with spider age, but larger spiders have been found to include a greater volume of silk in their webs. The figure to the right shows (a) that the overall stopping potential of the web increased isometrically (proportionally) with spider size even though (b) the stickiness per capture area increased at a rate lower than is predicted by isometry (isometry is indicated by the dashed regression line). The ability of the web to stop and retain prey is improved by larger spiders packing more silk into into their webs as well as tougher and more flexible silk threads. The results of this study suggest that by concentrating their silk resources, adult spiders are able to target larger and faster-flying prey (Sensenig, et. al, 2011).

Responding to a Changing Environment 

Although changes in web properties associated with a spider’s physical growth have been studied extensively, little research exists that examines the role of a spider’s ecology and environment on plasticity of web architecture and building behavior.

One study, however, found that female spiders living in a highly seasonal habitat exhibit a decline in foraging investment (measured by a decelerating size of web and low proportion of new silk in the web) at a relatively juvenile stage in development.  This decline in web investment was not observed in spiders in less seasonal habitats, suggesting that seasonal cycles affect the allocation of a spider’s resources into growth and development, as females must reach maturity and reproduce by the end of the breeding season (Higgins, 2006).