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
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 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
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
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.
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
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.