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Psyche 
[Vol. 90 
usually less than 30 seconds. At the end of June, defending ants and 
spiders cease patrolling the fronds entirely, although mature Meta- 
phiddipus protervus spiders and Formica subsericea ants can occa- 
sionally be found on new croziers which emerge periodically 
throughout the growing season. As with spring croziers, these 
summer fiddleheads are also patrolled systematically by ants, even 
though their nectaries appear to dry quickly under the hot sun. 
Concurrently with the declines in the ant patrols and the spider 
populations associated with bracken, there is a significant increase 
in herbivore damage, largely from adapted insects. Damage in- 
creases as adapted insect populations peak in mid to late summer, 
despite the “toughening” of the bracken with increasing concentra- 
tions of tannins and silicate, and despite the fact that available 
protein has declined by over 40 percent (Lawton, 1976). Any herbi- 
vore damage done at maturity, however, will affect proportionately 
less of the plant biomass than if the plant had incurred the damage 
during the crozier stage. Even minor chewing or sucking damage on 
the newly-emergent croziers can destroy part or all of the apical 
bud, or cause lodging of the plant at maturity if the rachis is wea- 
kened. Lodging or individual pinna or the entire frond is especially 
common in bracken plants attacked by minute gall-forming/ mining 
microlepidopterans, as yet unidentified. These mining insects can 
stunt 50 to 90 percent of the potential growth of a given pinna, 
possibly because they feed on internal vascular tissues and cannot be 
reached by patrolling ants or predaceous spiders. 
Summary 
Darwin (1877) was among the first to point out that the secretion 
of the bracken nectaries is very attractive to ants and that the ants 
may thus serve in some capacity to defend the ferns (Lawton, 1976). 
The arthropod defense system found in Michigan may help to 
explain why herbivorous damage from both adapted and non- 
adapted insects is minimal in the crozier stage. Bracken fern has a 
well-developed “arsenal” of potentially toxic secondary plant com- 
pounds that may also serve to deter or inhibit insects from attack. 
Yet, despite a relatively herbivorous-free period during its early 
growth stage, a diverse community of adapted herbivorous insects 
inflicts moderate to heavy damage later in the summer months. 
