Males in some species have distinctive midline processes on the second sternite (S2) (star) and often also on the sixth (S6) (solid arrow). In Bembix furcata, these processes are quite diagnostic. Although this would seem to makes species ID trivial for male B. furcata, there are two complications. First, these processes can be greatly reduced in some individuals, and S2 not apparently bifid, particularly in small males. Second, to see these processes (or the sternites at all), requires a nearly lateral or (ideally) ventral view. Most photos are taken from above.

The lateral view of the clypeus in this male matches the description for Bembix furcata: strongly protruberant, evenly arched in profile (dotted arrow).

Bembix furcata

In Bembix furcata males, S2 is strongly projecting (star) and often apically cleft to form two points (‘bifid’); S6 has a broad and complex projection (arrows), including a pair of angles at the outer sides and a short, blunt apicomedial point.

Male and female Bembix are best distinguished on the basis of the number of metasomal segments visible dorsally. That is, a count of the tergites. Males have 7, females just 6. Antennae also differ in the number of flagellar segments (males with 11, females with 10). However, apical segments are often short and may be difficult to count accurately in many field photos.

Bembix furcata

In this male the clypeus (dotted pink arrow) is protruding and largely white, although black laterally and apically; the labrum (solid green arrow) largely black, but white-cream laterally. The mandible is pale in colour, the base just visible tucked in behind the labrum.

Note also the large, arched process on S2 (star).

Bembix furcata

In this species the vertex (star) is well below the level of the eye tops (line). The front basitarsus (arrow) is slender, narrowly margined black along the outer edge, and bears 6 slender, pale amber pecten spines. Note too that the following three tarsal segments are quite slender (not expanded or modified).

Bembix furcata

In this species, flagellomere 5 (F5) is slightly excavated beneath, F6 more strongly so, and F7 spinose beneath (arrow). Compare to Fig. 134 (Evans & Matthews, 1973).

Bembix furcata

In this female, the clypeus (arrow) is very strongly protuberant and prominent laterally. It is bright yellow but with a large, black spot mediobasally.

Bembix furcata

Note the small lateral yellow streak on the mesoscutum, just above the tegula (star). The scape (arrow) is black above, yellow below.

The clypeus in this female is wholly yellow, without the black basal mark seen in some other individuals of the same species.

Bembix furcata

A full frontal view is necessary to assess the level of the vertex summit (star) with respect to the eye tops. Here the vertex is well below eye level.

Species vary in the width of the frons (double-headed arrow) relative to the eye height. In this female the frons is broad, the inner eye margins nearly parallel.

Differences in mandible shape between species are subtle, but do provide useful information. Here the mandible has a strong cutting edge (dotted arrow), described by Evans & Matthews as “an oblique cutting edge between the apex and the tooth on the inner margin.”

The number of antennal segments differs between the sexes. Females have just 10 flagellar segments, while males have 11.

Bembix furcata

Of particular importance is the structure and colour of the front basitarsus (arrow), including the number of ‘pecten’ spines. In all Bembix species, tarsal segments 2-4 bear two pecten spines each but the number on the front basitarsus varies from 6 to 42.
Here there are 6 pecten spines on the front basitarsus, which is quite slender. Also of note is the darkened, slightly lobed outer edge.

The spur on the inner apex of the front tibia (green star) is distinctive in some species. Here it is unmodified, ‘simple’.
From this angle, the midline of the clypeus is visibly elevated (red star). The shape of the clypeus is a useful feature for distinguishing between species, although it can be difficult to discern in field photos.

Bembix furcata

An anterior view of the front legs displays the colour and number of pecten spines, and the shape of the basitarsus itself (arrows). In this female the basitarsus is long and slender (not broadly expanded), mostly yellow but with a darkened outer edge, weakly lobed at the base of the spines. The six spines are long, and amber in colour.

The clypeus in this female is elevated mediobasally (star).

Bembix furcata

While colour patterning typically shows at least some variation within a species, it still provides a useful piece to the ID puzzle.

Two of the thoracic regions of note are the pronotum and the mesopleura. Note that in Bembix, the pronotum is much lower than the mesoscutum. It is often largely concealed in dorsal view, so lateral shots are helpful.

Note too the large pronotal lobe (star), which is extensively yellow in this species.

This angle also demonstrates why the labrum (arrow) can be difficult to see – it is often tucked away under the head.

When digging, females will usually have the mandibles open and forward of the labrum, making their colour easy to determine. In this female they meet the description of ‘yellow’, as the dark apex is universal in Bembix and so is not mentioned in the summary table of species descriptions.

Bembix furcata

Many Bembix species are extensively, densely hairy (‘setose’). And these hairs readily trap sand and dirt, making it very difficult to see the colour pattern of the underlying structure. Just another of the challenges of species identification from field photos!

The six metasomal tergites confirm this as a female. Note how each tergite (the dorsal plate of the segment) extends laterally. The sternites (the equivalent ventral plates) are not visible from this angle.

Bembix furcata