The only other reddish bee we've seen in the area is Diadasia tropicalis, but males of that species (like that shown below), do not have red tegulae or antennae
Male bee - Genus?
Size: est 6-7 mm (male)
Associated plant at NBC:
This male bee, found feeding on goldenrod, flew away before we could snag more photographs of it.
This is a small bee -- we estimated its size at about 6-7 mm. In addition to red tegulae, the bee has red femora and antennae (including the scapes) -- even part of the abdomen (S1) appears to be partly red. We're completely stumped by this one. Is it a male Exomalopsis mellipes?
February 8 response form Jack Neff: " Your red bee is presumably a male of Exomalopsis mellipes which is a fairly robust species with red legs and metasoma. All the North American Diadasia (Dasiapis) - (ochracea, olivacea and tropicalis) are little tan bees whose males have a pale yellow clypeus and mandibles and usually a yellow labrum while in the females the yellow maculation is limited to the mandibles. Diadasia ochracea is by far the most common member of this group so having common male tropicalis and female ochracea sounds like you have one of the two, but not both. Not all specialists recognize tropicalis but it and ochracea can be distinguished by the color of the integument of the hind femora (red/reddish in tropicalis - the usual tan in ochracea) and the punctation of the center of the scutum (sparse or near absent in ochracea, dense in tropicalis). The map of ochracea in the Snelling paper is a bit misleading as it omits its distribution in the US. Diadasia ochracea is actually widespread in Texas and occurs in the Valley.
The other male Exomalopsis has the orange hair of the hind legs and is what is commonly called birkmanni. Timberlake suggested it might be only a subspecies of solani and I tend to think it is only a color variant of solani as I have not found the genitalic differences Timberlake mentions. You could use either name."
These are photographs of a bee identified last fall as a male Exomalopsis snowi. This bee measured 7mm. It does not have red antennae, and its eyes are blue-gray rather than green
Exomalopsis birkmanni? male
Size: 9 mm (male)
Associated plant at NBC:
A large number of male bees like this were found mobbing a Texas sage bush where female Exomalopsis birkmanni with bright orange hind legs were feeding. (This is the same bush where we found the bee you identified earlier as a female E. birkmanni, shown below.) The hairs on the male bee's bottom leg segments are yellowish-orange. The hairs on the abdomen are long, pale and dense.
This is a bee identified last year as a female E. birkmanni
This is one of the female Colletes bees we found feeding on t he same seaside goldenrod plants as the male bee you identified as Colletes birkmanni. All of the female Colletes bees we're seeing on the goldenrod have the same rust-colored thorax hairs. (The female Colletes birkmanni identified last year also had this trait.) The females lack the specialized sternum hairs found on the male bee. (Photos of last year's female and of this year's male are shown below the latest photos of this new female.)
Size: 12 mm (female)
8-10 mm (male)
Associated plants at NBC:
Plant Family: Asteraceae
Female bee found a year ago, in November 2018
Male bee found a week ago, in October 2018