Abstract.Agelena labyrinthicaClerck spiders were raised in the laboratory at three diet levels. Growth, reproduction and the pattern of nutrient extraction of each spider were monitored. The extraction of proteins, carbohydrates and lipids by each spider was analysed on three occasions, covering the immature and mature stages. More nutrients were extracted the less well‐fed the spider, and females extracted more nutrients than did males. Nutrients were extracted most completely during early growth and, especially protein, by females in the reproductive phase. Protein was extracted more completely than lipids or carbohydrates. The relative amounts of the three nutrients extracted changed significantly with time, indicating that spiders are able to adjust their detailed feeding behaviour to their immediate needs. Field collections over the season showed that most spiders in the field grew approximately as those on the medium laboratory ration for most of the tim