Masoncus Spider: A Miniature Predator of Collembola in Harvester Ant Colonies

Symbionts are common in nests of Pogonomyrmex harvester ants (Lavigne 1969, Hunter and Farrier 1976, MacKay 1981 and 1983, Wray 1938). Over ten species of arthropods were found inhabiting Pogonomyrmex badius (Latreille) nests near Tallahassee, Florida. Springtails were especially common; literally thousands of white entomobryids and isotomids, were found running through nest chambers. The entomobryid was Pseudosinella rolfsi Mills, a species often found in ant colonies. The isotomid was an undescribed species in what may be a new genus closely related to Folsomia, Proisotoma and Cryptopygus. Perhaps the most interesting symbiont was a small undescribed spider of the genus Masoncus Chamberlin (Linyphiidae: Erigoninae). These spiders were about 2 mm long (Fig. 1). Their legs and cephalothorax were pale orange, while the abdomen was slightly darker and grayish. Immature spiders were pale cream colored with a grayish abdomen. Very little is known about the natural history of Masoncus spiders. According to Millidge (personal comm.), these spiders are taxonomically similar to the genus Tapinocyba. Masoncus spiders in P. badius nests are apparently predators of the symbiotic Collembola. On several occasions, actually observed these spiders carrying dead collembolans, although did not see how they were captured. These spiders can spin silk, but probably do not use webs for prey capture because have never observed more than a few strands of silk in any nest chamber. Symbiotic Thyreosthenius spiders in Britain also prey on Collembola (Bristowe 1939). Mites were very abundant and might be a secondary source of food for young spiders. The ceilings and floors of nest chambers were often covered with droves of small mites (4 species) slowly "grazing" on the substrate. These mites belonged to the families