The 14 larval habitats of this acid fresh water swamp produced 18 spp., for which the seasonal histories are given. A seasonal history was usually governed by the vegetative protection as detd. by water level, and it did not always coincide with that in the uplands. Aedes aurifer, A. canadensis, and A. implacabilis, the most common and pestilent early spring Aedes, developed in marginal grasses when water level was highest. Populations dropped in late May and early June when the water level dropped below this protective grass. Later previously submerged vegetation appeared, in which Anopheles walkeri, Culex apicalis (the most abundant species), and Uranotaenia sapphirina bred until late Oct. Then the water level again rose to produce conditions similar to that of late May and early June, whereupon they disappeared. Anopheles walkeri, the predominant anopheline, was confined to the river; any abatement measures would include chemical treatment or removal of grassy edges, or fluctuation of water level by dams. A. punctipennis predominated in bordering pools and uplands. A. quadrimaculatus occurred only in the uplands. Of the exptl. vectors of equine en-cephalomyelitis, Aedes triseriatus and A. vexans were rare; upland the latter bred profusely, along with A. atropalpus, A. sollicitans, and A. cantator. The numerous sphagnum pools produced few economic spp.; shallow grassy pools in open areas and cranberry bogs produced hoards of Aedes. Chemical treatment of grassy edges of this flat swamp during late Mar. and Apr. is recommended in preference to drainage or filling. 10 additional spp. are recorded from the uplands.