1939] Resemblance of Systropus to Wasps 21 
mon Systropus macer Loew may be readily mistaken for a 
species of “Ammophila”, but it has the habit, frequently 
seen in dipterous mimics of wasps and bees, of resting on 
the leaves of plants even during the brightest hours of 
sunshine. 
Among the Oriental and Indomalayan species the resem- 
blance to vespid wasps is not nearly so close, but nevertheless 
very striking. In the case of Systropus numeratus de 
Meijere of which I collected a male at Bangkinan, Sumatra, 
during May 1937, it would appear that the model is Steno- 
gaster micans Sauss. 1 as this wasp was flying very abun- 
dantly in the vicinity at the time the Systropus was taken. 
The two are of approximately the same size, but the gaster 
of the wasp is much stouter and the yellow markings on the 
thorax are larger, darker and do not coincide in size or posi- 
tion ; likewise the wasp is brilliantly spotted on the sides of 
the gaster which is not the case in the fly. Nevertheless 
when alive the close resemblance is unmistakable although it 
is not borne out by a too critical comparison of the pinned 
specimens. 
Another species, Systropus varipes Edwards, collected 
near Pematangsiantar, Sumatra is much smaller with 
darker legs and abdomen, and although quite wasp-like, is 
less conspicuously so and no vespids that resemble it at all 
closely were observed flying at the same time. Several of 
the small social species which are there common were pres- 
ent; all of these are much stouter and could not under any 
circumstances be confused with the Systropus. 
In general, the species of Systropus in this part of the 
world are “vespoid” mainly by reason of a conspicuous 
spotting of the thorax which is marked with light yellow. 
Although the pattern varies, the basic arrangement of mark- 
ings is of one type with permutations in shape and size. The 
coloration of the abdomen is black, varied with reddish 
brown or dull yellow, the reddish usually at the base and the 
yellow on the apical segments or venter. 
In the Nearctic “ammophiloid” species the pale spotting 
of the thorax disappears and the reddish color is restricted 
to the petiolar basal segments of the abdomen while the 
iRindly identified for me by Dr. Jos. Bequaert. 
