1. 1.

    Flies of the genus Syrphus aggregated at specific sites in the field (‘lecks’). Flies at leeks were always capable of ‘instant’ take-of, even at ambient temperatures of 10 °C or less.

  2. 2.

    The flies regulated their thoracic temperature by a combination of basking and shivering. During hovering flight in sunshine thoracic temperature rose 12–14 °C above the ambient temperature.

  3. 3.

    The flies engaged in frequent brief chases while at the lecks.

  4. 4.

    At an air temperature > 18 °C the flies at the leck remained in hovering flight most of the time.

  5. 5.

    The vibration frequencies of the thorax during shivering and flight ranged from about 100 to 200 Hz at 10–27 °C, though at a given temperature and spike frequency the vibration rate during warm-up was higher than the wing-beat frequency (assumed to be the same as thoracic vibration frequency) during flight.

  6. 6.

    During shivering, but not in flight, there is a tendency for the indirect flight muscles to be activated in synchrony.

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