Sexual Dimorphism

Sexual Dimorphism is a curious phenomenon in nature where one gender is larger than the other. Some examples are:

• Spiders (Redback spider)

Seen in this video is a male Redback spider mating with a female. The male is the far smaller spider on the females abdomen. It is common after mating has occurred that a the female will eat the male, simply because he has outlived his purpose. 

• Tarantula

Commonly with Tarantula mating, the female will come forward to strike the male with its fangs, but the male has hairs on its legs that are designed to catch the females legs as she strikes and therefore complete mating. Unfortunately for him, he doesn't always manage to catch the legs and ends up as dinner!

• Crocodilians

https://taxo4254.wikispaces.com/Crocodylus+porosus

With many crocodilians it is the opposite to spiders, and the male is indeed bigger than the female. With crocodiles this can lead to an interesting problem when mating where the male is much heavier than the female, and is in danger of crushing her. Their solution to this is to breed under the water, where the male can float.