Nesticidae - Eidmanella pallida
Size: 2.24 mm (male); 2.90 mm (female)
Group Guild Status
Eutroglophile Predator Common
This nesticid spider is wide ranging, occurring from far south central Canada throughout most of the USA and south to Central America and the West Indies (Paquin and Hedin 2005), and is common in cool, damp habitats such as deep plant litter, boulder piles, and other similar habitats as well as being a common resident of caves in these regions. Some cave populations of the species show evidence of troglomorphy (Paquin and Hedin 2005). The population of this species in Kartchner Caverns does not exhibit obvious morphologic adaptations to the cave environment. They occur anywhere in the moister areas of the cave where adequate prey supports the species, and are particularly common in areas that receive the annual guano deposits from the resident bat maternity colony. On the guano deposits they will erect their webs in voids among rocks embedded in the guano, but more commonly occupy drip cones in the guano. During summer when the invertebrate activity on the guano is high every drip cone in the guano deposits is occupied by one of these spiders in their web. They spin their webs at about the middle of the height of these cone-shaped depressions. They are most likely primarily consuming various mites that bloom in enormous numbers when the bats return to the cave each spring, but likely supplement their diet with other invertebrates that they can capture, including the sciarid and cecidomyiid gnats that breed in the fresh guano. The spiders suspend their round, bright-white egg cases in their web (see photo at left). Males are most commonly encountered during this active season when they search out the females to mate. At other times of the year the males are more evenly dispersed throughout the cave. As the bat activity wanes towards the end of summer it is not unusual to see the young spiders in the webs with the female. During the recent study we observed eggs and young in the webs with females between November and February. The initial study reported that egg cases were observed in May and October. We suspect the species typically has a single generation per year in the cave, although in areas away from the annual guano deposits this may vary. E. pallida is a common eutroglophile in Kartchner Caverns.
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