Responses to yesterday’s Mystery Photo ranged from immediate deletion by a reader (due to the unappealing nature of the photo), to guesses including “bee butt,” “caterpillar mouthparts” and “deer tick.” Most responders, however, guessed correctly – the photograph was of the spinnerets of a Black-and-Yellow Garden Spider, Argiope aurantia.
Most spiders have six spinnerets — organs located on their abdomens from which silk is extruded. The individual spinnerets move independently yet in a highly coordinated manner. Each spinneret is dotted with many tiny spigots, through which various types and thicknesses of silk are extruded. The strong muscles that move the spinnerets also force liquid silk through the narrow spigots. This pressure, as well as external pulling by the spider, rearranges the liquid silk molecules into a solid but flexible thread. Although spider web silk is only about one millionth of an inch thick, weight for weight, it is stronger than steel (but not as strong as Kevlar). Unlike in the Mystery Photo, the spinnerets in this photograph are extruded and in use.
Naturally Curious is supported by donations. If you choose to contribute, you may go to http://www.naturallycuriouswithmaryholland.wordpress.com and click on the yellow “donate” button.
Unlike spiders, whose spinnerets, or silk-spinning spigots, are located at the tips of their abdomens, caterpillars’ spinnerets are located underneath their heads. The most prominent white structure with a black band around it is the monarch caterpillar’s spinneret, in which its silk glands are located. The smaller structures are called maxillary palps and are antennae-like sensory devices. Prior to metamorphosing into a chrysalis/pupa, the monarch caterpillar draws silk through its spinneret, and forms a small, well-anchored button of silk. The caterpillar clasps this button with a structure called a cremaster, located at the tip of its abdomen, from which it suspends itself upside down. Soon thereafter its skin splits, revealing a gold-dotted, green chrysalis from which an adult monarch butterfly will emerge in two weeks.