1983] 
Douglas — Defense of bracken fern 
319 
Bracken may (in part) be protected by compounds such as thiam- 
inase and cyanogenic glucosides, but our research of the past three 
years shows that bracken at the very least supplements its passive 
chemical defenses with a mobile, predaceous arthropod defense 
community. This community includes at least 5 species of ants and 
10 species of spiders that are initially attracted to “axillary nectar- 
ies” (AN) secreting a nutrient-rich sap of sugars and amino acids. 
Our research shows that bracken “turns on” these nectaries during 
the rapidly-growing crozier stage, and turns them “off” after the 
pinnae are fully expanded. During the secretory stage, ants patrol 
and defend the pinnae from all intruders, including potential herbi- 
vores, other species of ants, and other predaceous arthropods such 
as spiders. However, the immature spiders also utilize the AN secre- 
tions, stalk arthropods within the developing canopy, or construct 
webs over the opening pinnae, turning them into effective traps with 
the AN enclosed as “baits.” 
Bracken’s apparent immunity to insect attack during the crozier 
stage may be due not so much to the toxicity of its secondary 
compounds, but to the continuing coevolution of the AN and their 
attendant, predaceous arthropods that patrol the pinnae or other- 
wise rid them of herbivores during bracken’s crozier stage. The 
bracken-arthropod system may be one of the most unique and com- 
plex hierarchies of symbiotic relationships to be found in a primitive 
plant-arthropod system. 
Acknowledgments 
This study was supported in part by NSF grant DEB-8005581 
(Gillian Cooper-Driver, Principle Investigator), and conducted at 
the Hope College Research Station, Holland, Michigan. I thank 
Gordon VanWoerkom and Annmarie Baldiga for their invaluable 
assistance in the field and laboratory. I also thank Drs. Irene Baker, 
Susan Koptur, and Peter Atsatt for use of unpublished information. 
Drs. O. Taboada, H. D. Blocker, R. E. Beer, M. DuBois, C. D. 
Michener, A. Brady, G. Byers, O. R. Taylor, W. H. Wagner and 
especially G. Cooper-Driver assisted me in various stages of this 
project and the preparation of the manuscript. 
