Who likes the Nectar of Aloe vera and little Petunias?

We try to keep our environment as natural as possible. We let the desert be desert and if we plant we try to stick to endemic plants. But some things were here when we bought the place. We ripped out ice plants and roses, but the Aloes got permanent residency because they are as desert adapted as our Agaves - just to a different desert. Coming to us from down under (South Africa) some also tend to bloom here in winter ...

 Their nectar is appreciated - by Gila Woodpeckers, Hummingbirds and Orioles, Verdins and by honey bees.  Of course, those are foreign imports as well. The woodpecker ingests them gladly in addition to the nectar. In South Africa, many Aloes seem to rely very much on birds for pollination, but honey bees also play an important role. (CT Symes et al. South African J. of Botany, Vol. 75, Issue 4, Oct. 2009)

 Not far from the Aloes, Cacti and Penstemon are blooming. The cacti may not all be endemics of the Sonoran Desert, but at least they came from near-by Baja and Chihuhua. Honey bees pretty much ignore them, but native cactus bees and little green sweat bees find those first cactus flowers within minutes. 

Anthophora bees are hovering among the Penstemons that they love and also nectar on the Creosote bushes that are the character plants of our sand flats.
 

 For the first time we had mini petunias in hanging pots this year and they surprised with an abundance of yellow and deep red flowers all winter long. They also have a weak fragrance. Our Costa's Hummer was mildly interested when his feeder was occupied by honey bees and nothing else was blooming. But he very much prefers the little Desert Honeysuckle and Cape Honeysuckle. I thought the Petunias, like the purple Barrio Petunias, might attract moths, but if so I missed it. An early Whitelined Sphinx instead hovered around our blooming basil plants, soon joined by the Costa's hummer.

But today I got a surprise: the yellow petunias had a yellow visitor: a Two-tailed Swallowtail. While Giant Swallowtails are rather common here thanks to numerous citrus trees in most yards, the Two-tailed is a butterfly of the sky islands where it patrols tirelessly along canyons and creeks. I most often saw it nectaring on thistles. We live in the lower desert of Saguaros, Creosotes and Ironwoods, and I have rarely seen a Two-tailed Swallowtails even  in the Tucson Mountains that are closest to us.

This nice and fresh looking guy payed several extended visits to our yellow petunia.   

The most common desert swallowtail is the Pipevine. In early spring it also appreciates Penstemon flowers while the summer generations have more divers choices.

I combined these examples of flowers and their visitors to point out that there is no great randomness in those pairings.  The flowers all offer nectar, and the visitors all seek those sweet calories but  the selectivity of those visits is caused by visual, chemical and structural characters of the flowers. Flowers with nectar evolved to attract pollinators, but a good pollinator is not a generalist that may squander precious pollen, but a faithful specialist that sticks to just one kind of flower at a time. So flowers evolved to limit access to their nectar to those specialists that evolved with them. This means of course that only flowers and pollinators that evolved together in the same part of the world can be perfectly in tune with each other. So our endemic bees stick with our endemic penstemons and cacti. Generalist honey bees and birds service aloes that are global transplants. Butterflies seem to be beneficiaries of  floral offerings, but due to their long legged anatomy they do not necessarily contribute reliable pollination services. By cross or maybe self pollination, our Aloes bear fruit, the penstemons are reseeding very nicely, the cacti produce well - only the little petunias have yet to show any inclination to make seeds, even though their flowers seem to be complete with all parts necessary. No idea what's going on.