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 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 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 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

The major visible plates along the dorsal midline of the mesosoma are: pronotal collar (low in Bembix, relative to the mesoscutum); mesoscutum (often simply called the scutum); scutellum; metanotum (very short); and the propodeum. When the wings are in the usual position at rest, the propodeum is obscured, as it is in species with particularly dense setae (hairs).

The U-shaped yellow mark on the mesoscutum is referred to as a discal mark. In some individuals (and species), the discal marks are much narrower than this, and the segments of the U are often not connected.

Bembix variabilis (tentative ID)

Image courtesy Reiner Richter, iNaturalist sighting 25727992

The features shown in this image are diagnostic for Bembix palmata males. The bright yellow clypeus in concave apically, has prominent round lobes laterally (curved solid arrow), and has a small median, basal ridge (star). The labrum is depressed near the base (dotted arrow), and also bright yellow. And the shape of the extremely broad front basitarsus (straight arrow) is unique.

Bembix palmata

Image courtesy Reiner Richter, iNaturalist sighting 147447501

The best chance to see the sternal process of males is when they are feeding at flowers. This species has a high ridge on S2, right-angled at the apex (straight arrow).

The yellow marks on the sides of the propodeum (curved arrow) are also visible from this angle. Note too the yellow marks on the extreme lateral sides of T1, highlighting the extent to which the dorsal tergites wrap around ventrally.

Bembix palmata

Image courtesy Reiner Richter, iNaturalist sighting 147447501

The uniquely shaped front basitarsus (straight arrow) of Bembix palmata is worth showing again. Note too the broadly expanded lobes of front tarsomeres 2, 3 and 4 (stars).

The shape of the male antenna is another feature that can helpful in species recognition. Modifications tend to start at flagellomere 5 (curved arrow), and in this species it is strongly spinose. Compare to Fig. 121 (Evans & Matthews, 1973).

Bembix palmata

Image courtesy Reiner Richter, iNaturalist sighting 105595939

Although the diagnostic features in females of this species are not as pronounced as in the male, they are nevertheless enough for a species ID (when taken in combination with colour patterning).

As in the male:the clypeus is broad with a median carina basally (star); the labrum is depressed basally (dotted arrow); and the front basitarsi are expanded (solid arrows) as are the following tarsomeres.

Note too the vertex level with the eye tops (line). This is the not an uncommon condition, but it does contrast with some other extensively yellow species such as B. flavifrons.

Finally, in this species the female typically has a pair of black spots on the yellow clypeus. This too is a widespread pattern, seen in many species (yet often highly variable within a species).

Bembix palmata

Image courtesy Reiner Richter, iNaturalist sighting 66902356

The five species of the Pectinipes species group are characterised by their numerous pectin spines. All have at least 10, and some as many as 42! This female has 12 I can count, and probably more. Compare to Fig. 36 (Evans & Matthews, 1973).

Bembix flavifrons (tentative ID only)

Image courtesy Reiner Richter, iNaturalist sighting 150716071

There are few Australian Bembix that can be unambiguously identified to species level based on the colour pattern alone … but this one can! Commonly referred to as the ‘Panda Sand Wasp’, Bembix vespiformis is unmistakable. There is some variation … the apical segments are not always orange (particularly in the east), and T2-4 may be all black or have white spots. But the large, tapered white spots on T2 are a consistent feature.

Bembix vespiformis

Image courtesy Kerry Stuart, iNaturalist sighting 198711178

Despite the distinctive colour pattern, I like to check as many other features as possible against a putative species description. For example, here the colour of the mandibles, legs, mesoscutum all fit with Bembix vespiformis … as do the 7 long, dark pecten spines on each of the front basitarsi (arrows).

Note that this is one of many Bembix species widely distributed across continental Australia.

Bembix vespiformis

Image courtesy Kerry Stuart, iNaturalist sighting 195650631