Webspinners (Order Embiidina), silk-spinning insects, are unique in their ability to spin silk by stepping against the substrate with their front feet while multiple silk strands issue forth. Webspinners construct silken dwellings that house mothers with their young, sometimes in large colonies. The use of silk within the order varies from extensive structures covering tree trunks to scant amounts applied as an adhesive for materials gathered to form dwelling walls. In the laboratory, we investigated the question "how costly is it to spin silk?" as the first part of our study examining how the costs and benefits of silk production affect the evolution of primitive social behavior in these insects.

To determine the relationship between metabolic rate and behavioral activity, including silk-spinning, we developed a method that employs simultaneous event recording (using The Observer) and metabolic rate recording (using a Qubit Systems carbon dioxide analyzer). We quantified the activity of individuals placed in a respiratory chamber for 30 minutes. Subsequent analysis of behavioral repertoires allowed us to identify three distinct female categories, based on overall activity: resters, wanderers and spinners. Compared to their resting state, webspinners produced carbon dioxide at twice the rate when when they were spinning. However, the apparent metabolic costs of locomotion and of spinning silk were not significantly different, suggesting that spinning is as energetically costly as walking and climbing.

Our method of coordinating behavioral and metabolic recordings appears efficacious, and should provide a method for an extensive comparative study as we investigate the range of silk-spinning strategies within the order.

Paper presented at Measuring Behavior 2002 , 4^th International Conference on Methods and Techniques in Behavioral Research, 27-30 August 2002, Amsterdam, The Netherlands

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