Ancylandrena Mining Bees in our back yard

Updated repost from 2014
 Our house is built on sand. It sits on a little mesa (elevation) consisting of soil that was excavated to put in the basement. Over the years I found out that we share this site with many sand loving, digging insects, tarantulas and scorpions. And please don't think that that is a problem. Some of these guys may even keep out others that we would like less.

The little dark parasitic bee, waiting close to the nest entrance

 Yesterday I was reading at the bedroom window when I noticed a dark little bee zigzagging and descending repeatedly out of sight under the window. Time to investigate.
When I got outside, she was resting on a flat rock. In the soil around it were several small, round holes about 5 mm in diameter. Another bee buzzed closer, circled, landed next to one of the holes and slipped inside.

A mining bee exiting the nest entrance

 This bee was larger, plumper, and lighter than the little observer. It stayed in the hole for a long time. While I was watching, two more bees arrived and crawled in. for over 10 min no bees left as far as I could see. Then the smaller bee flew up, circled shortly and also crawled into the hole. Several other bees of the bigger kind entered 5 other holes, all in an area of less than a square meter.  Eventually bees also exited the hole that I was watching, but too fast to get any good pictures. Peak activity seemed to be around 10 to 11 am.
Today I came better prepared. For example, I found a way to sit instead of crouching over the hole for what turned out to be long waiting times. So I got some video of the larger bees that clearly shows that several bees are using the same entrance and are under ground simultaneously. Incidentally, the little bee was inside during that time as well. This time I trapped her and three exiting larger bees to get a closer look. I had an idea by now that I was dealing with mining bees and a clepto-parasite, but I found that I didn't have these guys in my photo collection yet.

Ancylandrena sp. Doug Yanega det.

 Indoors, I put each bee into a white ceramic bowl and covered it with a clear plastic container. It took a while for them to calm down. If they had been beetles, they would have experienced a short cool-down in the fridge by now, but bees just don't look right when they are cold. So instead, I got the chance to take a few quick photos, some OK, some blurred and some out of focus, of each bee before she took off for the window. No harm done, they were easily coaxed back into the container.
John Ascher commented on BugGuide:

The expected species is A. larreae if creosote bush is blooming nearby (lots of it!)

The yellowish tan thoracic hairs are consistent with that species.
She should have a conspicuous yellow blister at e base of the mandible.

Hexepeolus rhodogyne, Doug Yanega det.

In the close-ups, the parasitic bee looked somewhat beat-up. Maybe her life as an uninvited guest was not quite as easy as it seems. But her visits in the nest, concurrent with those of several 'owners' did not seem to create any disturbance.

Several of my Flickr and facebook connections are bee specialists, so I posted the photos there and on BugGuide.

From Doug Yanega came the response:  "The latter is Hexepeolus rhodogyne, and it is a cleptoparasite in nests of Ancylandrena (the first bee). It wasn't until the 1990's that the host-parasite association of these taxa was confirmed, as I recall. The genus Hexepeolus contains only that one species".

John Ascher added a link to the 1994 paper: Biologies of the bee genera Ancylandrena (Andrenidae, Andreninae) and Hexepeolus (Apidae, Nomadinae) : and phylogenetic relationships of Ancylandrena based on its mature larva (Hymenoptera, Apoidea). American Museum novitates ; no. 3108

It turned out that BugGuide had an image of a mounted specimen of the parasite, but only an empty, prepared, page for the host. So I was able to fill in both with white backgound-life-close-ups and action in situ shots:

BugGuide Info Page

As for the species id, in Discover Life I found a description of a rare Tucson specialty, A. rozeni, but it would be difficult to identify it without comparative material:  A. rozeni - This is a rare species with records restricted to Arizona, specifically known from the Tuscon area - The male appears closest to that of A. larreae though slightly smaller, has a shorter clypeus, has shorter antennae, has smaller light markings in the paraocular area, is less densely pitted anteriorly on the scutum, hairs sparser in the anterior of the scutum, and has a greater proportion of dark hair on the upper areas of the head - The female appears most similar to that of A. timberlakei, although it may be differentiated by the presence of some degree of a tan or yellowish brown mound on the base of the mandible, a greater proportion of dark hairs in the upper areas of the head, the fact that all hairs anterior to the middle of the tegulae are white, and that there is a greater proportion of light-colored hairs on the scopa (2)
 Anyway, I preserved a specimen.

So to summarize, Ancylandrena is a mining bee. In spring males and females emerge from underground cells. They mate, and the females dig nest burrows in sandy soil. Mining bees collect pollen in the long hairs of the tibial scopa of the hind legs. (They do not  have a 'pollen basket' like honey bees and bumble bees). They construct small cells containing a ball of pollen mixed with nectar, upon which an egg is laid, before each cell is sealed. Although not social, several individuals seem to be sharing at least a nest entrance (Solitary, communal ground-nesting). As many insects do, they provide provisions for their offspring, but they are not around to guard the larvae while these are growing up. Clepto-parasites like the one I observed commonly make use of this arrangement to raise their own brood. Many of these clepto-parasites, like this one, are in the subfamily Nomadinae (Cuckoo Bees). They usually lack the hairs that are used by their relatives to collect and transport pollen. There are a number of strategies to get parasitic eggs into a provisioned nest. In this case the cleptoparasitic bee just followed the host bees to get her eggs into the brood chambers before they were closed. In Rozen's study several eggs of Hexepeolus rhodogyne were attached to the inner wall of the brood chambers while the larger egg of the host bee was sitting on the pollen ball. This explains why Hexepeolus was around for several days entering the same nest repeatedly: she had to access the chambers that were just in the right stage of construction.

PS: I was busy at an art show for three days, but when I checked again on Monday, 3/24/2014 there were still Ancylandrenas entering the same nest. I also found another nest about 60 meters south on a berm planted with cacti and creosote bushes.

Update April 2018: In the following years  I did not see these bees nesting again. But my observation and photos made it into a great new bee book 'The Bees in Your Backyard' by J S Wilson and O M Carril Princeton University Press 2016.

 
 In April 2018, on our neighbors' potted Aloe, I found a group of sleeping males most likely of the Ancylandrena species Ancylandrena rozeni. Id by John Ascher from my photos.
These guys lack the brown hair of the ones I photographed in 2014 and are silver-grey all over. No yellow blister under the mandibles.

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.