Wolf spiders in the genus Pirata are common, often locally abundant, inhabitants of many moist or mesic habitats. However, relatively little is known about the ecology or life history of these spiders. Here we present data collected during 2000–2001 on female size, offspring size and clutch size for two populations (Ball Gulf, Hardscrabble Creek) of Pirata sedentarius from western New York. In both populations, mean offspring size was less variable than was female size, clutch size or total clutch mass. At Ball Gulf, 67% of females produced two egg sacs and 48% produced three sacs. Clutch size declined across the egg sac sequence for all females. Female size, measured as cephalothorax length, was uncorrelated with mean offspring size in all cases. However, larger females produced larger and heavier clutches during 2001 for both populations; female size was uncorrelated with these variables during 2000 at Hardscrabble Creek. Larger clutches from both populations contained more offspring, and larger clutches contained smaller offspring at Hardscrabble Creek in 2001. We found a significant offspring size-number trade-off at Ball Gulf, while at Hardscrabble Creek this trade-off was marginally significant in 2001 and non-significant in 2000.