Deceiving No-see-ums, Pollination of the Pipe Vine

Pipevine Swallowtail (Battus philenor) nectaring on ButtonBush, not Pipe Vine

Our most common desert Swallowtail is called after it's foodplant Aristolochia, the Pipe Vine. It is a A trailing or climbing vine with stems up to 3 feet (0.9 m) long. The 1 inch (2.5 cm) long, arrow-shaped leaves are usually dark brownish-green when growing in full sun.

Southwestern Pipevine Aristolochia watsonii

 The tubular-funnel form flowers are about 1¼ inches (3.8 cm) long, green with brown spotting.Supposedly the flowers reminded earlier botanists of the pipes that Dutch sailors used. As the great grand daughter of a German pipe smoker, I can see the similarity.  By the way, the Swallowtail lays its eggs on the plant, but it does nothing to pollinate the flowers. Pollination is left to much less obvious little insects.

Ear of a packrat left,  pipe vine flower right

It would be much more fitting to call those fluted flowers Mouse Ears. Even a human eye can see a physical similarity. More interestingly, there is a smell that is musty, and, well, similar to the inside of a rodent ear. This is the olfactory stimulus that attracts  flies of the family Ceratopogonidae (Biting Midges)

No-see-um, Ceratopogonidae (Biting Midges)

 They are small, blood sucking insects, some of the no-see-ums that pester humans and other animals on warm, humid summer days and often seek access to the bloodvessels in rodent ears that are especially highly vascularized in desert species (thermoregulation!).
The Pipe Vine grows usually in the shady, humid micro climate under shrubs -ideal micro habitat for the little flies. Drawn by odor and ear-like shape of the flower, and expecting a blood meal, the midges enter.   The shape of the flower and inward-directing hairs in its narrowed throat  trap the flies temporarily, often over night when pollen release is at its peak.. In their attempts to escape the flies dislodge pollen and transfer the pollen they may have already bought with them to the stigma. In the morning the pollinated flower releases the captives. Because the flowers provide super-stimuli, the flies' instinctual reaction is to fall for the same deceit over and over.

The fruit of Southwestern Pipevine Aristolochia watsonii, and Swallowtail caterpillars feeding

 So this is another striking example how plants secure the pollination services of insects. No reward (nectar) is offered in this case.  

Thank you to lepidopterist Fred Heath who reminded me of this interesting story during our recent nature walk in Sabino Canyon. Also see Mark Dimmit https://www.desertmuseum.org/books/nhsd_aristolochiaceae.php