Based on the number of BugGuide posts,
Physocephala tibialis is likely the most commonly encountered species of thick-headed fly (Conopidae) in the US and Canada. At the time of writing here, there are almost 200 images of about 140 distinct individuals of
P. tibialis posted on BugGuide...far more than for any other species in the family.
Typical
P. tibialis is distinctively blackish overall...accented with various patches of white distributed as follows: on the face and laterally on the lower frons; on the bases of the tibiae; in thin pollinose bands at the distal ends of the first few abdominal segments; and sometimes in short, vague, pollinose, dash-like markings on the humeri (or "shoulders") of the thorax. The white of the tibiae is often tinged reddish, and there are sometimes small reddish areas near the joints of the tibiae and femora...and less often very thin reddish lines along the sutures of the thoracic sclerites.
Among BugGuide images of more than 130 distinct individuals of
P. tibialis posted over the decade between February 16, 2004 and June 1, 2014, there were just 2 posts of aberrant individuals where the
"T"-shaped marking on the frons...which is characteristic of the genus
Physocephala...was
reddish rather than black as in normal
P. tibialis, see the thumbnails below:
A 
B 
Then, in the period between June 1 and June 24, 2014...less than a month...posts of seven new
P. tibialis individuals were made, four of which were aberrant!! One of these had a reddish "T" on the frons like the previous two:
C 
But the other three exhibited anomalously reddish coloration on the thorax....from relatively subtle to strikingly extreme:
D 
E 
F 
These aberrant individuals raise a number of questions:
* What might be causes or explanations for these aberrations?
* Are they genetic flukes...or perhaps developmental or environmental effects?
* Might they have taxonomic and/or systematic significance?
Various posts of teneral Conopinae suggest that, immediately after pupation, much of the adult body is initially reddish:
...and it presumably "cures" over a period of time (hours?) to the normal color pattern for each given species. Might this explain some of these apparently anomalous individuals?
The interesting species
P. floridana is said by Camras to be closely related to
P. tibialis. As currently understood, its range is centered in Florida, but reaches west to at least east Texas and north into Georgia. It is typically more robust and "chunky" in form than
P. tibialis, and has significant red on the thorax, head and legs. Might the aberrant
P. tibialis here bear an interesting relationship to
P. floridana?
In this context, there is one other post from Brooklyn, NY which I previously speculated may have been a waif of
P. floridana:
G 
...but which may be an aberrant form of
P. tibialis close to those in thumbnails
D and
E above.
Here is a
map link (created using the ACME Mapper web site) showing the locations of the 3 "reddish-T aberrants" (marked A, B, and C) and the 4 "reddish thorax aberrants" (marked D, E, F, and G) appearing in the thumbnails above. Note that there is no obvious geographical clustering among the two types of aberrants...they appear fairly widely distributed over the bulk of the eastern US range of
P. tibialis.
Any comments or further thoughts, observations, and/or insights into these matters would be welcome and much appreciated.
