Insects and arachnids are other examples of sexual dimorphism where females are considerably larger, as the sole purpose of the male is copulation. (Some males compete against each other and that makes their size matter.)

In many reptile species, females are larger and sometimes stronger than males, which contrasts with the general mammalian trend where males are typically larger and stronger. This difference is driven by fecundity selection—the evolutionary pressure for females to maximize egg production—compared to the sexual selection pressure that often favors larger males in mammals.

1)Fecundity Selection (Egg Production) In reptiles, a female’s ability to produce more or larger offspring is directly proportional to her size. Larger females can accommodate larger abdominal cavities for carrying more eggs or delivering bigger, more robust hatchlings. In many lizard and snake species, selection favors females that can produce larger clutches, leading to the evolution of larger, stronger female bodies.

2. High-Resource Demand for Reproduction Producing eggs (oviparity) or carrying young (viviparity) requires a massive investment of energy and physical space, far more than the sperm production of males. Females are selected to be large to handle this strain, whereas males do not face this constraint and are often limited to size increases only for fighting.

3. Reduced Male-Male Competition In many reptile groups, particularly many snakes, males do not fight each other for access to females. In such species, male size is not selected to be massive. If female fecundity (egg count) is more important for survival than male mating aggression, females evolve to be the larger sex.

4. Resistance to Aggressive Mating In some lizard and snake species, males are highly aggressive and often chase or force females to mate. A larger, stronger female is better equipped to survive these aggressive interactions.

5)Contrast with Mammals Mammals: Sexual selection is intense, favoring massive males that can fight for access to a harem of females. Pregnancy/nursing is very costly, making smaller females often more efficient for resource management, leading to sexual dimorphism where males are larger. Reptiles: Reproduction is focused on sheer volume of eggs rather than protecting a territory. Because a “big mother is a better mother” (more eggs), selection favors female size. Note: In reptiles with high territorial aggression (like certain Anoles or Crocodilians), males are often larger/stronger, showing that the trend depends entirely on the species’ mating behavior