The difference in size between males and females of a species is known as sexual size dimorphism (SSD). It is quite common in nature, and especially in spiders. It is usually the females that are larger.

Female spiders are often said to grow so big because it means they can produce more babies. However, scientists say that this does not explain why the males of so many species are so small.

Now, researchers working with males and females of 13 different spider species say that a tactic called bridging explains this puzzle. Bridging is when spiders in trees or bushes release a line of silk that attaches to another plant. They then climb upside down across their bridge to reach new areas.

The scientists say that small spiders can climb better across bridges, and that this gives them more opportunities to find females and mate with them. Species that don’t use bridging also show less difference in size.

The video below shows the small male spider watching the female spider wrap up lunch...