MASONCUS SPIDER: A MINIATURE PREDATOR OF 
COLLEMBOLA IN HARVESTER ANT COLONIES 
By Sanford D. Porter 
Department of Biological Science 
Florida State University 
Tallahassee, Florida 32306 
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 spe- 
cies often found in ant colonies. The isotomid was an undescribed 
species in what may be a new genus closely related to Folsomia, 
Proisotoma and Crvptopygus. 
Perhaps the most interesting symbiont was a small undescribed 
spider of the genus Masoncus Chamberlin (Linyphiidae: Erigoni- 
nae). 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, I actually observed 
these spiders carrying dead collembolans, although I did not see 
how they were captured. These spiders can spin silk, but probably 
do not use webs for prey capture because I 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 
145 
