Yesterday researchers announced the discovery of the largest web-spinning spider in the world. Nephila komaci, which spins meter-wide webs, is 40 mm long. But males of the species (pictured clinging to the underside of the female) are only 9 mm.
The spider was discovered in South Africa, and a group of researchers officially described the species in a paper published in PLoS One yesterday evening. Spiders in the Nephilia family all exhibit what's called extreme sexual size dimorphism - in other words, the females are a lot larger than the males, and usually eat the males after mating with them. You can see from these images that the males of N. komaci really are so small compared to the females that they could be mistaken for a post-coital snack.
The researchers also analyzed the evolution of these spiders, and concluded that what we're seeing is a tendency towards female gigantism rather than male dwarfism. Because the female spiders survive better the larger they get, they have evolved to be huge. The males, on the other hand, wind up passing along their sperm to the next generation if they mature early (i.e. when they are smaller) and can climb really well. And thus, you get tiny males and giant females.
via PLoS One