Why Male Spiders Are So Small

Male spiders may be tiny compared to their female counterparts in part because it makes it easier for them to get around and spread their genes.

Scientists studied different spiders’ aptitude for bridging — sending out strands of thread that get carried by the wind to another spot, and then crawling across — by placing them in a wind tunnel and watching them move around. They discovered that smaller spiders made bridges more often, and that the technique was more common in spiders with a pronounced difference in size between the sexes.

In species where bridging is a very common mode of locomotion, small males, by being more efficient bridge builders, will enjoy more mating opportunities and thus will be better at competition to reach receptive females.  This may lead to a selective pressure for smaller size.

The picture on the right is of a female and male orb-weaver spider.

Original article here.