Numbers
Currently there are 20 valid species in this genus worldwide,
C. aerarium and C. cyaneum occur in North America.
Identification
Biology: The genus Chlorion is a member of the tribe Sceliphronini which includes the following common genera: Sceliphron, Chalybion (mud daubers), Podium (makes simple mud cells under bark or in pre-existing cavities in wood), and Chlorion (fossorial). Being the only member of the genus that dig their own nests, Chlorion aerarium is most common in loose gravelly or sandy soil. C. aerarium is not as attached to human habitations as the two common mud daubers C. californicum and S. caementarium.
Morphology:
Sceliphronini are characterized by the following:
-Gaster with a cylindrical petiole composed of sternum only, first tergite removed
to the apex of the first sternite.
-Jugal lobe of posterior wing comprising nearly all of anal area.
-Tarsal claws with a single median tooth.
This genus is similar to Chalybion superficially, but differs from it in the following characters:
-Tarsal rake (females only).
-Head and thorax sparsely hairy.
-Propodeum with a U-shaped dorsal enclosure defined at least posteriorly by a
semicircular sulcus or furrow (Chalybion has at most a median sulcus or pit)
-Chlorion is generally larger than Chalybion, and in Chlorion
the head is more produced at the temples and vertex giving this genus a distinctly
different head shape.
Extract from Dr. Ascher’s comments
here:
...Chalybion and Chlorion are very similar
Note greenish or purplish color of many Chlorion vs. blue in Chalybion
Also note the shape of the pronotoum, which is more strongly notched in Chalybion
Finally, the head of Chlorion is broader
…
John S. Ascher, 17 February, 2008 - 10:02pm
Food
Chlorion aerarium preys on crickets, C. cyaneum on cockroaches.
Remarks
Nearctica lists two species in North america C. aerarium and cyaneum
