|Hyles lineata by Chris Barnhart|
This raises the question of how they find their food sources. They tend as a group to prefer long tubular white flowers and are "suckers" (brazen pun intended) for sweet smelling flowers with rich nectar that they can find at a distance.
A new study reported in redorbit.com suggests that they improve their odds by sensing minute differences in the humidity of flowers. The moisture around the opening of the blossom relates directly to the amount of nectar available and drops off if an insect has depleted the nectar pool. The researchers at the University of Arizona further demonstrated that the white lined sphinx moth (Hyles lineata) would preferentially hover and try to feed on artificial flowers if the humidity of the "blossom" was raised as little as 4% from the ambient air, the gradient found on their normal nectar sources in nature.
“The metabolic cost of hovering in hawkmoths is more than 100 times that of a moth at rest,” said Goggy Davidowitz, the study’s co-author and a UA professor. “This is the most costly mode of locomotion ever measured. An individual hawkmoth may spend 5-10 seconds evaluating whether a flower has nectar, multiply that by hundreds of flowers visited a night, and the moth is expending a huge amount of energy searching for nectar that may not be there. The energy saved by avoiding such behavior can go into making more eggs. For a moth that lives only about a week, that is a very big deal.”
|Snowberry Clearwing- Roy Thompson|
Hawk moths have the longest tongues in the insect world, up to 14 inches long. Darwin described a deep star orchid of Madagascar with a tubular flower that was 11 inches long with only an inch of nectar at the bottom. He faced ridicule when he suggested that a hawk moth must exist with a long tongue which specialized in pollinating the orchid. Years after his death he was vindicated. This BBC video demonstrates this form of mutualism by a day feeding hummingbird moth.
More information on hawkmoths in general is at Wikipedia and this US Forest Service site.