Some of the most commonly encountered spiders on Earth belong to the the family Linyphiidae. Yet much about the family's estimated 4,400 species remains a mystery, due in no small part to the fact that many of these species look almost identical, even under a microscope.
The similarities between female members of the Linyphiidae subfamily Erigoninae are particularly strong. So how does one go about characterizing so many similar looking spiders? Simple: you stare at their genitals.
See, spiders are often distinguished from one another for classification purposes by their genitalia. Females are characterized by anatomical variations in their epigynum—a small, shield-like plate located on the belly that covers the openings to their sperm-collecting organs.
For the last 13 years, Nina Sandlin (who by day works as the online operations manager for American Medical News) has spent one day a week going through the painstaking process of examining the epigyna of female Erigonine. But Sandlin does more than peek. She also photographs these spiders. She even posts the images on the internet in an album called LinEpig, where arachnid collection managers can go to help them identify erigonine females in their own collections.
According to Scientific American's Meera Lee Sethi:
People who hear about what Nina does every Monday in a small back room on the third floor of the Field tend to call it "spider porn." After I watched her image Sougambus bostoniensis, Diplocentria bidentata and Diplocentria rectangulata a few weeks ago, I'd say that they're right—right, that is, assuming that the process of making adult films is also exhausting, frustrating, meticulous, and fraught with tremendous difficulty, punctuated by the occasional moment of transcendence.
So why does Sandlin do it? After all, as Sethi mentions above, photographing these spiders is an incredibly demanding task. Consider, for example, that many of these spiders are no larger than a mote of dust. Now imagine trying to photograph a mote of dust's genitals. Now understand that when Sandlin started out with this project, she was photographing spider parts with a point and shoot digital camera, but that even today—equipped with a stereoscopic Olympus research microscope, a USB digital camera attachment and a copy of Photoshop—her photoshoots still demand borderline superhuman levels of patience and care.
And remember, this isn't even Sandlin's full time job; it's effectively a part-time, unpaid, personal mission. So, again, why her? Because, quite frankly, for as important as Sandlin's classification work is, it would seem that almost nobody else is either willing or able to do what she does. Sethi writes:
Nina's in a unique position to do this work. Most volunteers and students don't have the "erigo-knowledge" that Nina has gradually built up, while academicians can't spare time from the molecular work and phylogenetic tree-making that their publications require. So now the arachnid collections of America are benefited by the efforts of an amateur who is weirdly dedicated, relatively knowledgeable-and a little bit insane.
You can read more about Sandlin's remarkable dedication to the classification of Erigoninae over at Scientific American.