none V. acadica (Sladen) typically nests in decayed logs in heavily forested habitats. Many aspects of its biology are characteristic of the V. rufa (L.) species group: one worker-rearing comb, loose-weave network of the nest envelope, ribbonlike suspensoria above the top comb and cordlike pedicels between subsequent combs, short colony duration, small colony size, and foraging only for live prey. An ichneumonid parasitoid and vertebrate predators may have an important impact on V. acadica population dynamics, but the obligate social parasite, V. austriaca (Panzer), probably has a more serious effect on the host. Inquilines successfully usurped 7 of 17 postemergence colonies. Parasitized colonies were smaller than nonparasitized ones, and unlike typical V. acadica reproductive (large-cell) combs where both queens and males are reared, only V. austriaca females were reared in the large cells. Nutrition; Feeding behaviour; Reproduction; Reproductive behaviour; Breeding site; Locomotion; Behaviour; Social behaviour; Associations; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Host parasite relationships; Ecology; Population dynamics; Animal constructions; Land and freshwater zones; Nearctic region; North America; USA Fannia canicularis (Fanniidae); Associations; Vespula acadica (Hymenoptera); Nest cavities of declining colonies; USA; Idaho; Latah County; St Joe National Forest; Washington; Fields Spring State Park; Association with declining hymenopteran nest Sphecophaga vesparum burra (Ichneumonidae); Hymenopteran hosts; Vespula acadica; Prevalence in normal & social parasite infested colonies; USA Vespula acadica (Vespidae); Foraging; Nesting site; Subterranean, depth; Flight; Hovering; Social organization; Associations; Fannia canicularis (Diptera); Nest cavities of declining colonies; Nest and burrow fauna; Social parasitism; V. austriaca; Social parasite, host population structure effect; Hymenopteran parasites; Sphecophaga vesparum burra; Prevalence in normal & social parasite infested colonies; Prevalence; Nest & pupal hymenopteran parasites; Population structure; Hymenopteran social parasite effect; USA; Nests; Structure; Idaho & Washington; Idaho; Latah County; St Joe National Forest; Washington; Fields Spring State Park; Nesting biology, prevalence & effect of associates Vespula austriaca (Vespidae); Sex determination; Hymenopteran host cell type relationship; Social parasitism; V. acadica; Social parasite, host population structure effect; USA