Synonyms and other taxonomic changes
All three species were previously genus Argyrodes
3 species in BugGuide's range (North America north of Mexico).
All three species roughly 4mm or less in body size. Males are much smaller than females.
One point: males have projections or modifications on their clypeus and/or eye region, females typically do not.
Females - I have Exline and Levi 1962, which lumps all these related genera under Argyrodes. It maps all two-tipped abdomen species to the trigonum group, which was later moved to the genus Neospintharus, making this Neospintharus. ~Joe Lapp, 20 June, 2011
baboquivari - known only from AZ
furcatus - southeastern United States (SC, GA, FL, AL, MS, AK, LA, TX)
trigonum - eastern United States and southeastern Canada (ON, QC, NB, NS)
These small cobweb spiders can sometimes be kleptoparasitic and found in the webs of larger species like Nephila clavipes, Gasteracantha, and Argiope (to name a few). They are so small they often go unnoticed by the web owner, thus allowing them to sneak away with the small insects that get caught in the web. Sometimes more than one, or many, of these can be found in a single host web. A variety of species can share the host web, as well.
Species of Neospintharus
were previously placed in Argyrodes
Exline, H. & H. W. Levi, 1962. American spiders of the genus Argyrodes (Araneae, Theridiidae). Bulletin Museum of Comparative Zoology Harvard 127: 75-204. (available online in the Biodiversity Heritage Library here