Nutrient-specific foraging is the ecological theory that generalist
consumers select food resources based on their nutritional content.
While laboratory experiments support this idea, it has yet to be
demonstrated in invertebrates in the field. We combined dietary DNA
metabarcoding with prey availability data and macronutrient content in
the field to analyze nutrient-based prey choice. We show that spider
nutrient intake and prey choice deviates from what we would expect if
individuals randomly chose their prey. Through a novel nutrient-based
taxonomy and null modelling, we reveal a stable average macronutrient
intake. There was disproportionate foraging for different macronutrients
by individual spiders. Although, this might be expected as individual
prey are biased toward particular nutrients and individual spiders were
at different stages of nutrient balancing when collected. This finding
suggests that spiders are redressing nutritional deficits to obtain a
target nutrient intake, as would be expected of nutrient-specific
foraging. This evidence for nutrient-specific foraging under field
conditions is a significant advance, extending our understanding beyond
lab-based behavioral assays to now resolving complex real-world systems.