SPIDERS LIVING AT WASP NESTING SITES: 
WHAT CONSTRAINS PREDATION BY MUD-DAUBERS? 
By Martin S. Obin 1 
The nests of mud-daubing wasps (Hymenoptera: Sphecidae) are 
excellent sources of spiders (Peckham and Peckham, 1898; Rau, 
1935; Muma and Jeffers, 1945; Dorris, 1970). Females of these soli- 
tary wasp species construct mud nests during the late spring and 
summer. They provision each brood cell with a number of spiders 
which they capture and paralyze by stinging. The wasp lays an egg 
on one of these spiders and, upon hatching, the larva consumes all 
the spiders within the brood cell. When development is complete, 
the new adult wasp chews a hole in its brood cell and emerges. A cell 
in the nest of mud-daubers such as Sceliphron caementarium or 
Chalybion californicum may contain in excess of 25 spiders. It 
seems likely then that mud-dauber predation may be a significant 
factor influencing population dynamics and evolution of those 
spider genera taken as prey (see also Eberhard, 1970). But this view 
of wasp and spider interactions is incomplete. The same sites at 
which mud-daubers nest are also used by both wandering and web- 
building spiders for capturing prey and tending eggs. Mud-dauber 
nests themselves are often used by spiders for these activities. In 
fact, among the group of spiders active at mud-dauber nesting sites 
are species that are regularly taken as prey by those same spider- 
hunting wasps. Intrigued by this fact, I initiated field studies that 
addressed the following questions: 
1. What groups of spiders are found living at nesting sites of 
mud-daubers? 
2. What is the nature of the interactions between wasps and spi- 
ders at these sites? 
3. If wasps do not hunt spiders at nesting sites, what factors 
constrain them from doing so? 
'Department of Zoology, University of Florida, Gainesville, FL 3261 1 
* Manuscript received by the editor July 25, 1982. 
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