Large orb-weaving spiders in temperate zones always mature in Autumn. A model based on laboratory feeding experiments and insect trap samples from an old-field in Michigan was used to simulate orb-weaver foraging behavior in various habitats and seasons. Seasons of peak energy return rates in habitats used by old-field orb-weavers indicate that prey availability plays a role in determining phenologies of large spiders. The minimum body-size to which the constraint applies in the model corresponds to the lower size-range of strictly Autumn-maturing orb-weaver species.