Tarantulas are among the most recognizable spiders, belonging to the family Theraphosidae, which includes over a thousand species found across the globe. Understanding the distinctions between male and female tarantulas involves looking closely at their physical characteristics and the profound differences in their life histories. Questions frequently arise regarding the differences between the sexes, particularly concerning their overall size and structure.
Understanding Sexual Size Dimorphism
Yes, female tarantulas are typically larger than males, a phenomenon known as sexual size dimorphism. This difference is most noticeable in the overall bulk and weight of the spider, rather than the length of its legs. Females possess a much more robust, heavy-bodied appearance with a significantly larger abdomen. This shape results from their reproductive biology, which requires substantial internal space and energy reserves.
In contrast, mature males often appear “leggier” and thinner. While their leg span can sometimes rival or exceed that of a female of the same species, their cephalothorax and abdomen remain comparatively slender and smaller. The degree of this size difference varies considerably across the tarantula family. The overall body mass and volume are the truest indicators of the female’s larger size.
Morphological Indicators Beyond Size
Once a male tarantula reaches his final molt, he develops specialized external structures that distinguish him from a female, regardless of size. The most prominent of these are the tibial hooks, or mating spurs, which appear on the underside of his front pair of legs. These hooks are used during copulation to secure the female’s fangs, preventing her from biting the male.
A second set of unique structures develops on the male’s pedipalps, the short, leg-like appendages near his mouth. The tips of these pedipalps become enlarged and bulbous, forming the emboli, which are the specialized sperm delivery organs. The male uses these to transfer sperm from a silk sperm-web into the female’s reproductive opening. Females lack these secondary sexual characteristics, retaining their simpler pedipalp structure.
Evolutionary Reasons for Female Bulk
The primary biological driver for the female’s greater size and bulk is the necessity of reproduction, a concept known as fecundity selection. Female tarantulas must produce and store a substantial number of eggs, requiring a much larger abdomen and greater body mass. A single egg sac can contain hundreds or even thousands of eggs, demanding significant internal capacity and energy investment.
This increased size also serves a protective function, allowing the female to store extensive energy reserves for long periods between feedings. These reserves help her survive while guarding the egg sac or during times of resource scarcity. Therefore, the female’s evolutionary pressure favors a large, robust body that maximizes her reproductive output and longevity.
Lifespan and Behavioral Divergence
The life histories of male and female tarantulas diverge dramatically after they reach sexual maturity. Female tarantulas are built for permanence, often staying in or near the safety of their established burrows and continuing to molt and grow for many years. Females of certain species can live for 15 to 30 years.
Conversely, the mature male embarks on a “wandering” phase immediately following his ultimate molt, driven solely by the purpose of locating a mate. He typically stops feeding, dedicating his remaining energy to searching. This shift in behavior exposes him to predators and harsh environmental conditions, resulting in a significantly shortened lifespan. After reaching maturity, male tarantulas typically survive for only a few months up to one or two years.