Energy content of spider eggs.

The energy content of spider eggs was determined on samples from 12 species representing 6 families. These values ranged from 26.32 to 29.00 joules per mg ash-free dry mass with a mean of 27.30±SE of 0.27. The higher values were found in those species that overwinter as developmental stages within the egg sac. Rates of energy expenditure of developing eggs and spiderlings within the egg sac were only 7 to 19% of those of emerged spiderlings. The energy conserved by this reduction in rate of metabolism may facilitate survival without feeding during the potentially long periods of aerial dispersal by ballooning, a characteristic activity of most newly emerged spiderlings. The variation in mass-specific energy content is less than variation in clutch size and individual egg size on an intra-and interspecific basis. There was no correlation between energy content per unit egg mass and size of the female parent, egg size, or clutch size. Further analysis indicated that no single measure such as clutch size accurately represents the proportional amount of energy invested in reproduction in these animals.