The familiar spider’s web can be made by any of many species of orb-weaver spider. Most orb-weavers are shades of brown, grey or black, but not this one, in the Maine woods.
She waits in a hole at the center of her web. She is a female Micrathena sagittata orb weaver spider, only 8-9mm long, 1/3 inch. (The male is much smaller and more discretely colored, so it is rarely seen .)
Her abdomen is arrow-shaped (the two rear prongs are black, so they don’t immediately stand out from the background in the previous photo). She has spines at the sides and on her back, easier to see in this side shot:
She is named after Athena, the goddess of weaving, and sagittata meaning arrow-shaped, the same root as Sagittarius the Archer.
Elsewhere in the world there are other spiders with hardened abdomens with variously shaped spines. I saw this one in Koshi Tappu in Nepal three years ago.
It rejoices in the name of Hasselt’s Spiny Spider, Gasteracantha hasselti. Surprisingly , genetic analysis shows that they are not closely related to the American Micrathena, so the armored exterior seems to be an example of convergent evolution, with clear defensive advantages.
And the colors? Red and yellow often stand as a warning to would-be predators that you might be poisonous. Or they can be an enticement to potential mates, as they are thought to be in the Painted Turtle,
Or both? who knows??