Abstract: Larvae of Myrmeleon immaculatus in large pits captured both large and small prey, while larvae in small pits captured only the small prey. Larvae in small pits did not respond to large ants, although they always responded by sand-flinging to small ants. Larvae in medium-sized pits often captured large ants only after prolonged and vigorous sand-flipping. Larvae in large pits usually captured large ants with relatively little sand-flipping. Pit enlargement and pit relocation in the laboratory were not significantly correlated with reduction of rations in the first 3 weeks after a pit was built. However, after a month without food, larvae on the average moved once every 10 days, built successively smaller pits, and moved longer distances before building a new pit. In the field pits were dug primarily in response to microclimatological factors and possibly edge-effects. The presence or absence of suitable prey at a site, per se, had no effect on whether or not a larva would dig a pit there. We conclude that these sit-and-wait predators have a relatively large repertoire of behavior that enhances their foraging success, and we contrast it with previously made optimal foraging models relating to pit locations, pit relocations, pit size and ant lion responses.
Abstract: Bumblebees ranging in mass from 65 mg (the smallest workers of the smallest species) to 830 mg (the largest queens of the largest species examined) maintained similar average thoracic temperatures (TsubTh) while foraging, even though the passive cooling rates of these bees over this size range varied fourfold. Although the bees regulated TsubTh between apparent lower and upper set points despite wide ranges of body size (and over wide ranges of ambient temperature), they allowed TsubTh to fluctuate between set points. The foraging activity of queens was relatively independent of ambient temperature (Tsuba), but workers (and particularly the smallest workers were often excluded at low Tsuba. Although the size-related rates of passive cooling of drones was similar to that of workers, they did not maintain the same TsubTh as workers on some kinds of flowers.
Abstract: While foraging from the dense inflorescences of spiraea (Spiraea latifolia) and goldenrods (Solidago sp.), both workers and drones often allowed thoracic temperature (TsubTh) to fall below the minimum for flight. The bees were physiologically capable of maintaining a high TsubTh, but the periodic decrease in TsubTh was strongly correlated with ambient temperature (Tsuba). Decreases of TsubTh were unrelated to fuel reserves carried in the honey stomach. Drones foraging from the inflorescences were more likely to have low TsubTh than workers, even though on the average they carried several times greater fuel reserves in their honey stomach. Within workers, old or parasitized (by conopid flies) individuals were more likely to forage with low TsubTh than young an unparasitized individuals. Workers, unlike drones, showed an increasing tendency to decrease TsubTh with decreasing body mass. Although the decrease in TsubTh while foraging ('torpor'), with its associated sluggishness, appears to function as an energy-conservation mechanism, it could also be a risk-averting mechanism. By maintaining a high TsubTh and flight readiness, workers can 'gamble' on the chance of finding a new food source, unlike drones who do not have the hive's energy resources to fall back on if they deplete their supply of stored fuel.