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Fig. 11.1. The daily probabilities of attack and predation by crab spiders on a worker bumble bee and a worker honeybee (data from Morse 1986), and two values each for bumble bees and honeybees of overall daily disappearance rates of workers observed at the hive. (Data from Rodd et al. 1980; Goldblatt & Fell 1987; Wolf & Schmid-Hempel 1989; Dukas & Visscher 1994.)

honeybee specialist, although it occasionally takes other bees of similar size (Evans & O'Neill 1988).

The North American "bumblebee-wolf," P. bicinctus, mostly specializes on bumble bees. An aggregation of approximately 200 bumblebee-wolves observed by Gwynne (1981) was estimated to prey on a total of over 7500 bumble bees (Evans & O'Neill 1988). Armitage (1965) recorded 154 attacks by bumblebee-wolves on worker bumble bees foraging on clover and goldenrod flowers, 23% of which resulted in predation.

Hymenoptera predominate in the diet of most bee-eaters (Meropidae); honeybees are the most frequent species taken, although the European bee-eater (Merops apiaster) seems to prefer bumble bees (Fry 1983). Fry (1983) estimated that about 33% of the predation attempts by bee-eaters were successful.

Conopid flies (Conopidae) parasitized 12.7% of bumble bee workers in eastern Canada (MacFarlane & Pengelly 1974) and an average of 13.2% in Switzerland (Schmid-Hempel et al. 1990). In the latter study, the frequency of parasitation increased from 0% before June to a peak of 35% in

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