Bembix glauca Fabricius 1787

Bembix glauca Fabricius

Bembex [sic] glauca Fabricius, 1787:285, 286 [ Tranquebar; type in Copenhagen Museum],—Olivier, 1789:291 [brief description].—Fabricius, 1793:249 [brief description]; 1804:224 [brief description].—Jurine, 1807:175 [listed].

Bembex [sic] indica Handlirsch, 1893:771, 772, pl. 1: fig. 33, pl. 6: fig. 33 [, Ceylon, Decan; syntypes in Vienna, Hamburg, Berlin, Brussels, Zurich, Colombo]; 1895:1053 [listed].—Bingham, 1897:291 [redescribed].—Dalla Torre, 1897:506 [listed]. [All listed glauca as a questionable senior synonym.]

Bembix glauca Fabricius.—van der Vecht, 1961:59 [note on type; synonymized indica].—Bohart and Menke, 1976:546 [listed].

Handlirsch assigned indica to his monotypic indica Group, which should now be termed the glauca group. The group is distinguished by the strongly protuberant clypeus and extremely slender mandibles (index 2.8–2.9 compared to 1.7–2.3 in other species), and in the males by having the terminal flagellar segments relatively slightly modified, the midfemur smooth beneath and the second abdominal sternum with only a low median keel. It is also behaviorally distinctive, for it constructs a much deeper nest with more angles than any other species of the Indian subcontinent whose nesting habits are known.

The species is known only from the Indian subcontinent where all precise locality records are from coastal localities. Based on collecting experience in Sri Lanka (KVK), glauca appears to be restricted to the seashore where it nests in pure sand above the high tide mark. Handlirsch's record of indica syntypes from Decan is troublesome. No such locality is listed in the available Indian gazeteer. The label “Decan” may mean from the Deccan plateau, a highly unlikely locality for an essentially littoral species.

The identity of a pair listed in the key by Dahlbom (1845:491) as “26. Bemb. glauca nob. , India & Egypt” is puzzling. A pair of Bembix identified by de Beaumont as an unnamed subspecies of olivacea is in the Lund University collection that houses the Dahlbom collection. The male bears several labels, one printed “Coll/L.gh,” one on creamy paper with a handwritten “glauca” underlined and one on blue paper in the same handwriting, “glauca” not underlined. R. Danielsson advises that L.gh stands for S.I. Lungh who collected probably only in Scandinavia. The female bears only one handwritten label, “Egpt”; it may be the specimen misidentified as glauca by Dahlbom.

MALE.—Length 12.0–19.5 mm, forewing 8.0–12.0 mm, wing index 1.95. Mandible (Figure 23b) slender, straight, no cutting edge beyond acute subapical tooth, index 2.8; clypeus strongly protuberant and convex, 1.47 times as wide as high; least interocular distance midway between antennal sockets and anterior ocellus, 0.56 times eye height; center of vertex slightly below top of eyes; scape 2.6 times as long as wide; first flagellar segment 3.8 times as long as wide; terminal flagellar segments slightly modified, 7–8 slightly widened at apex, 9–11 slightly concave beneath; forebasitarsus 3.2 times as long as wide, with 6 pecten spines; midfemur smooth beneath, very rarely weakly serrate; tergum 7 shallowly emarginate at apex; sternum 2 moderately punctate, median keel low, not dentate at apex; sternum 7 swollen in middle, not carinate.

Color predominantly pale, mostly white or whitish yellow on head, tibiae, tarsi, and across middle of terga, pale yellow on middle of face, thorax, coxae, femora, bases, and apices of terga, and sterna, the following black: apical third of mandible, antenna above, narrow oblique streak from clypeus to side of antennal socket, paired triangular spots above antennal bases fused above, vertex except oblique band adjacent to ocellar triangle connecting below with broad stripe on front, scutum except broad, U-shaped mark in middle and broad stripe laterally, basal band rounded posteriorly on scutellum, narrow line on base of scutellum, mesosternum, narrow lines along episternal sulcus and meso-and metapleural sutures, narrow transverse band at base of propodeum, spot around spiracle, narrow lines along basal half of propodeal enclosure and small spot at its apex, small blotches on coxae, trochanters, femora, and foretibia beneath, several small spots on declivous surface of tergum 1, small paired elliptical spots on terga 1–6, those on 5–6 normally invisible because of being on retracted bases of sclerites, lateral spots on terga 2–6 occasionally lacking on posterior terga, irregular median stripe on sternum 2, basal spot on sternum 3, sterna 4–6 except for yellow spots of variable size on sides, and sterna 7–8. Wings hyaline; vestiture dense, pale, erect on base of clypeus, front, vertex, gena, thorax, and base of tergum 1, short and suberect on remaining terga, sparse and subdecumbent on sterna.

FEMALE.—Length 14.0–17.0 mm, forewing 10.0–12.0 mm, wing index 1.95. Mandible (Figure 23a) slender, straight, no cutting edge beyond acute subapical tooth, index 2.9; clypeus strongly protuberant and convex, 1.64 times as wide as high; least interocular distance 0.56 times eye height; center of vertex slightly below top of eyes; scape 3.0 times as long as wide; first flagellar segment 3.7 times as long as wide; forebasitarsus 2.8 times as long as wide with 6 pecten spines; scutum with small subcontiguous punctures; sternum 2 moderately punctate, more closely so laterally, medially with a narrow elliptical area that does not reach base or apex of sclerite; tergum 6 narrowly rounded apically, closely punctate except on a narrow median strip.

Coloration similar to that of male though pale markings less extensive as follows: clypeus with a median subbasal black spot, lateral stripe on face absent adjacent to ocellar triangle, vertexal stripe small, arms of U on scutum narrower, legs yellow, upper surface of forefemur dark, foretibia with a short stripe externally, terga 2–4 with apical dark bands, 5 with a short transverse dark stripe at apex, tergum 6 with a pair of small yellow spots, sterna 2–5 with progressively smaller lateral yellow spots. Wings and vestiture as in male.

LOCALITIES AND MONTHS OF COLLECTION (USNM unless indicated otherwise).—Sri Lanka, NORTHERN PROVINCE, Vavuniya District: Mullaittivu ( Nov; Colombo); Mannar District: Olaithoduvai, 10 mi W Mannar, 0–50 ft (, 3 Nov), Marichchukkadi ( Dec; Colombo). EASTERN PROVINCE, Trincomalee District: Kokkilai Beach (3 Nov). WESTERN PROVINCE, Colombo District: Pamunugama, sea level (10, 14 Jan, Mar, Sep), Uswetakeiyawa, 0–50 ft (, 3 May), Colombo (, 2 May, June; Colombo), Mt. Lavinia ( Feb, Colombo). SOUTHERN PROVINCE, Galle District: Bentota (2, 4 Aug, Colombo); Hambantota District: Palatupana, 0–50 ft (2, 9 Jan, Mar, Apr, Sep, Oct), Butawa Modera ( Dec; Colombo).

India, Madras: Pondicherry (3, Paris), Tranquebar (7 May; Corvallis). Kerala: Mahe ( Paris), Malabar (9, 5 Paris).

Bembix glauca Fabricius

This distinctive species was found in areas of fine beach sand along the coast. Other collectors also have taken it only at coastal localities in Sri Lanka, presumably on sand. Nesting occurred at Pamunugama, Colombo District, a tiny fishing village 12 mi N of Colombo on the west coast, and near the Wildlife and Nature Protection Society Bungalow, Palatupana, Hambantota District, on the extreme southeastern seacoast.

HABITAT.—There are no dunes at Pamunugama and the nests were in gently sloping pure sand several meters above high tide mark. Presumably these areas might be inundated during sporadic heavy storms. The sand was quite moist immediately below the surface. Although there are dunes at Palatupana, glauca did not nest in them but on the lee side (NW) of small hillocks, 1.0–1.5 m high and about 50 m from the ocean at an elevation of some 3 m above sea level, where they were protected from the constant SE breeze in March 1981. It may be that the species nests in flat sand at Palatupana during periods when the wind is not so intense.

Our most extensive notes were made 13 September 1980 at Pamunugama, where we found two small aggregations at 0900 separated by some 30 m. Several beach areas at Pamunugama were visited on 16 March 1981, but only one female was just beginning a nest.

ADULT ACTIVITY.—At Pamunugama in September 1980 females were already digging nests or bringing in prey to established nests when we reached the site at 0900. Males were flying low over the whole area, occasionally alighting on the sand, sometimes a pair circling around each other during flight. Females were beginning nests or bringing in prey between 0900 and 1030. One female digging a nest was interrupted occasionally by a male pouncing on her and attempting to mate. Later in the morning when she flew to her nest with prey, she was followed by a male that tried to mate when she landed at the nest entrance.

About 1030 both sexes began to take shelter from the increasing temperature on the surface and none was observed after 1100. Males entered open burrows and pushed up damp sand from immediately below the surface to block the entrance. The females ceased nesting activities, entered their nests, and pushed up damp sand to block the entrance. At 1430 when the temperature moderated the wasps were again on the wing and were still active when we left at 1545. Several males tried unsuccessfully to couple with flying females. The females confined their activities to brief flights, working on old nests or beginning new ones, but did not bring in prey.

At Pamunugama in March 1981 there were 6–8 males flying low over the ground in one area, occasionally fighting in pairs, alighting on the sand for a few seconds, or visiting flowers for nectar. There was only one female, just beginning to nest.

The first nesting notes at Palatupana were made 6–7 October 1980, a period marked by strong winds of variable intensity from the southeast and a thunderstorm the evening of the 6th with 8.5 mm of rain at the saltern several hundred meters distant. Three females were beginning nests. Several males were flying around but did not attempt to mate. We revisited Palatupana late in March 1981. On the 30th there were 6–8 males flying low over the area where glauca nested the previous year. This must have been prior to emergence of females, for we saw none in 1981.

Both sexes visited the pale blue flowers of a prostrate succulent plant, Hydrophylax maritima Linnaeus (Rubiaceae), for nectar at Pamunugama and Palatupana.

NEST CONSTRUCTION.—A female was digging a nest at Pamunugama at 0920. The sand already excavated was spread in a low spoil heap behind the burrow entrance over an area 2.5 cm long and 1 cm wide. As she deepened the burrow, she pushed sand up to the entrance, and backed out only after several minutes to kick it with her forelegs backward over the spoil heap. She emerged headfirst at 1013, but re-entered at once, continued digging and then spreading the excavated sand over the spoil heap. She had plugged the burrow by 1100 and had not emerged by 1545.

Nest construction at Palatupana was abnormal because of the strong winds and thunderstorm. Three females began nests between 0925 and 0942 on the bare NW lee slope of a small hillock. One burrow extended horizontally for about 20 cm at 0942. There was no further activity in any nest between 0945 and 1135. The burrow entrances were still open and the wasps were not in evidence. During the afternoon the winds intensified and drifting sand covered the burrow entrances, leaving only shallow dimpled depressions. I blew away the loose sand at the entrance to one nest and found that the burrow had not been blocked from within by damp sand. Apparently this nest, and presumably the other two, had been abandoned that morning because of the difficulty of excavation during the wind.

At 1155 on the second day at Palatupana a female was digging a burrow in the 45° slope on the lee side of another hillock. She had already begun two other burrows nearby, and occasionally stopped work on the third to dig in one of the other two. At 1201 she began still another burrow a few centimeters above and to the right of the first three. When I left at 1211, she was back digging in the third burrow. This nest was excavated at 1430 and we found that it had not been completed. The burrow penetrated at an angle of 15° to the horizontal for 31.5 cm, turned downward at 75° for 5 cm, and then turned at another steep angle for 11 cm where it ended without a cell; the wasp was not inside the burrow. The other three burrows were not sealed and were 1.0–2.5 cm long. These burrows were possibly aborted because of some unacceptable characteristic of the soil. They could not have been true accessory burrows that are made after the true nest has been dug.

NEST STRUCTURE.—Two excavated nests contained a partially provisioned cell. The burrow of one (Figure 1) penetrated the sand for 59.4 cm at an angle of 45°, turned more steeply downward for 7 cm, then turned backward, continuing at a steep angle for 13.5 cm, and terminated in a cell at a depth of 60.5 cm below ground level. The horizontal ellipsoid cell contained a wasp larva about a third grown, four whole flies 4.0–10.5 mm long, and fragments of three flies.

The burrow of the other nest (Figure 2) went in at an angle of 40° for 51.6 cm, vertically for 9 cm, then backward at a steep angle for 7 cm, then forward at a shallow angle for 12 cm, and terminated in a cell 48 cm below the surface. The cell contained a wasp larva about a third grown, three whole flies 4.5–5.0 mm long, and fragments of three flies.

A third nest was excavated at 1150 after the wasp entered the nest at 1055 and plugged the entrance from within. Earlier she had brought in prey at 0929 and 0931. This burrow went in at an angle of 40° for 45 cm and then continued at a shallower angle for 10 cm. The burrow was lost at this point and neither wasp nor prey was recovered.

The burrow of a fourth nest penetrated at an angle of 30° for 41.2 cm, then angled in another direction at 45° for 15 cm, then in still another direction at 30° for 5 cm, and finally backward at 30° for 15 cm. The wasp was found at a depth of 54 cm but the cell was not found, although earlier she brought in prey twice.

The burrow of one aborted nest at Palatupana went into the sloping sand of the hillock at an angle of 15° to the horizontal for 14 cm. Then it made a slight angle and continued downward for 17 cm. The burrow ended at that point and there was neither a wasp nor a cell at the inner end.

The extreme length and depth of the nests in which we found only a partially provisioned cell poses a question that can be answered only by additional observations. Would it not be advantageous for a species that expends so much energy constructing a long, deep, tortuous nest to make a multicellular nest?

NEST PROVISIONING AND PREY.—We observed prey being brought to the nest by four wasps. The fly was carried beneath the wasp, venter to venter, and was transferred to the hind legs when the wasp landed at the closed entrance. She rapidly scratched open the temporary closure with her forelegs and crawled into the nest, carrying the prey beneath her, protruding beyond the tip of her abdomen. During nine such visits the wasps remained inside for periods ranging from 30 seconds to 8 minutes (mean 2 min, 21 sec). The tempo of provisioning was frequently rather rapid but occasionally quite slow: one returned with prey at 0929, 0931, and 1055; another brought in prey at 1026 and 1037; a third came with prey at 0948, 0951, 0956, 1002, 1005, and 1027; and the fourth brought three prey at 1003, 1008, and 1010.

The wasps always emerged headfirst after taking in prey. Three of them spent from 30 to 60 seconds making a temporary closure by scratching sand from the spoil heap backward into the entrance. This closure was done in a more leisurely manner than when the closure was opened to bring in prey. One wasp twice varied the closing routine by excavating at the entrance and a short distance into the burrow for a minute or so before making the closure. The wasps flew off as soon as the closure was complete.

Both nests at Pamunugama contained a mixture of tabanids and muscoids, suggesting that the wasps were preying upon Diptera that were flying around the tethered water buffalo grazing nearby. Consolidated prey records from the nests and a prey taken from a wasp are as follows: