Key to British Male Platycheirus Incorporating the Main Infrageneric Groupings in iNat

It is best to interpret these keys with sight of quality pictures such as the excellent resource by Steve Falk

In constructing this I have used information from the helpful Book 'Britain's Hoverflies' by Ball and Morris, the key in 'Hoverflies of Northwest Europe' by M.P. van Veen and Steve Falk above.

Some of these species are next to impossible to ID from a photo, but I hope that this key might enable more of them to reach a finer level of ID.

For an overview of how the taxonomic groupings used by the UK Hoverfly Recording Scheme relate to the taxa available on iNat see here

Note that the distinctive rosarum and granditarsus have departed for Genus Pyrophaena.

This key is intended to be as useful as possible when IDing from photos, but this will frequently be impossible. Used with a little circumspection I hope it is at least helpful. I am very happy to be informed of any errors.

Males:

1. a. Abdomen with paired grey maculae; face and frons entirely grey dusted; frons is quite large when viewed from above; Foreleg unmodified in shape; femur with apical curled bristle.
b. At least some foreleg segments modified in shape; no curled bristle at the apex of the fore femur; if grey spotted then with at least some shining black undusted parts on frons.
Subgenus Pachysphyria

Subgenus Platycheirus
P. ambiguus

2
2. a. Foretibia not broadened towards the apex; at least foretarsi 1+2 enlarged to produce a smooth curved shape; if abdominal spots are orange then face produced beneath the tubercle into a blunt snout.
b. Foretibia broadened toward the apex; forebasitarsus enlarged in a smooth rounded shape or with pointed corners; face flattish beneath the tubercle.
Section manicatus


Subgenus Platycheirus cont…
4


3
3. a. Orange spots. Foretibia sharply broadened only at the apex; forebasitarsi greatly enlarged, significantly overhanging the tarsi on the inside and with an acute corner on the inside apex; posterior surface of forefemur covered with strong flattened black hairs; middle femur with deep anterior concavity; fore and middle femora never all yellow.
b. Orange or grey spots; Male foretibia broadening throughout most of its length; forbasitarsi expanded into a smooth curved shape; forefemur without flattened black hairs; middle femur without concavity; fore and middle femora may be yellow or not.
Section peltatus



Section albimanus
7



9
SECTION MANICATUS
4. a. Greyish Spots, face not produced forward into a blunt snout.
b. Orange-yellow spots, face produced forward into a blunt snout.

Section manicatus cont…
P discimanus
5
5. a. Face and frons shining black, mouth edge not quite projecting beyond the tubercle; foretarsi 1-3 expanded, pale and tapering towards 4-5 (black); scutum shining black.
b. Face and frons grey dusted; if scutum shining black then only foretarsi 1+2 expanded; mouth edge protruding past the tubercle or not.


Section manicatus cont…
P melanopsis

6
6. a. Mouth edge projecting a little beyond the tubercle; foretarsi 1-3 expanded, pale and tapering towards 4-5 (black); scutum grey dusted; broader bodied; abdominal spots reaching close to the hind margin of the tergites.
b. Scutum shining black; foretarsi 1+2 expanded; mouth edge not quite protruding past the tubercle; narrower bodied; spots not reaching close to the hind margins of the tergites.



P manicatus


P. tarsalis
SECTION PELTATUS
7. a. Larger species; spots on T2 well formed (but not large); middle tibia with moderate ventral swellings at 1/3 length and apex, the former with an indistinct tuft of moderate length black hairs.
b. Smaller species; spots on T2 poorly formed or absent; middle tibia with ventral swellings absent or strong and a distinct flag of long black hairs at 1/3-1/2 length.



Section peltatus cont…
P peltatus


8
8. a. Middle tibia with hardly any ventral swellings at 1/3 length or apex, but with an anterior hair tuft.
b. Middle tibia with pronounced ventral swellings at mid length and apex but no anterior hair tuft; a tuft of hairs arising from the apical swelling pointing upwards parallel to the tibia.
P amplus

P nielseni
SECTION ALBIMANUS
9. a. Normally greyish spots; spots never nearly filling the length of the tergites; if poorly formed and even absent on T2 then the foretibia widening gradually throughout its length, and not greatly expanded; forefemur with only one long posterior black bristle in the apical half (much longer than the surrounding bristles).
b. Normally orange-yellow spots; spots usually well formed, in many species more than 1/2 the length of the tergites; if spots very poorly formed and even absent on T2 then the forefemur expanded suddenly more towards the apex than the rest of the length and with a distinct tuft of black hairs prior to the apical expansion; forefemur may have more long black posterior bristles or not.
Section albimanus cont…



Section albimanus cont…
10



11
10. a. Spots normally fairly well formed except sometimes on T2 with hind margin sloping forwards medially; foretibia greatly broadened; Forefemur without a long wirey posterior bristle at the apex, but with two basal L-shaped tufts of tangled bristles.
b. Spots poorly formed, even missing on T2; foretibia only slightly broadened; Forefemur with a long wirey posterior bristle at the apex, but without basal L-shaped tufts.
P albimanus


P sticticus
11 a. Large orange spots (>1/2 length of tergites 3+4). Without two hooked tufts of bristles at the base of forefemur; metacoxae normal.
b. Small squarish orange spots; Two hooked tufts of bristles at the base of forefemur; metacoxae with finger-like process.
Complex clypeatus

Complex scutatus
13

12
COMPLEX SCUTATUS
12. a. Face and frons wholly silver dusted; spots on T2 well formed.
b. Frons dark or obscurely golden dusted; very obscure abdominal spots especially on T2 where they are usually missing entierly; middle tibia particularly hairy.
c. Frons black; abdominal markings well formed.
P. scutatus
P. aurolateralis

P. splendidus
COMPLEX CLYPEATUS
13 a. T2 with large spots (>1/2 length of tergite).
b. T2 with small spots (<1/2 length of tergite).
Complex clypeatus cont...
Complex clypeatus cont...
14
18
14 a. Hind leg black except narrowly yellow at the knee. T5 black. Foretibia exanded suddenly in the apical 1/3, rounded, curving in again toward the apex.
b. Hind femur, tibia and usually tarsi with some yellow. T5 with yellow markings. Foretibia expanded differently and not curving back in again.


Complex clypeatus cont...
P. podagratus

15
15 a. Hind femur and tibia yellow. Foretibia expanded suddenly in about the apical half, remaining parallel sided to the apex.
b. Hind femur and tibia with some black. Foretibia expanding more gradually from the base to the apex.


Complex clypeatus cont...
P. fulviventris

16
16 a. Forefemur without a basal tuft of long white hairs, but with a posterior row of long strong black bristles. Foretibia, although it expands from the base it contracts again at about 2/3 length before expanding again to the end; black hind border of tergites not much narrower than the width of the black midline.
b. Forefemur with a basal tuft of long white hairs, with or without a posterior row of long strong black bristles; Foretibia expanding continuously from base to apex; black hind border of tergites very narrow or absent - much narrower than the width of the black midline.




Complex clypeatus cont...
P. scambus



17
17 a. Forefemur with a posterior row of long black strong bristles.
b. Forefemur without a posterior row of long black strong bristles, instead with dense, mainly yellow, hair. Apex of middle femur with anteroventral black hairs bent backwards.

P. immarginatus
P. perpallidus
18 a. Notably slender species; pleura distinctly shining, undusted; Forefemur with long black hairs in the basal half sharply bent at their tips. Underside of forebasitarsus with a v-shaped incision. In direct comparison with P. europaeus, the spots on T3 longer.
b. Broader species, though *P. europaeus* is also quite slender; pleura at least partly dusted. Forefemur without such hairs. Underside of forebasitarsus with or without a v-shaped incision.



Complex clypeatus cont...
P. angustatus


19
19 a. Underside of forebasitarsus with a v-shaped incision. Fairly slender species. In direct comparison with P. angustatus, the spots on T3 shorter.
b. Broader species; Underside of forebasitarsus without a v-shaped incision.


Complex clypeatus cont...
P. europaeus

20
20 a. Underside of forebasitarsus with a short narrow pale bare area stretching from the base to a darkened pit in the basal half.
b. Underside of forebasitarsus with a longer narrow pale bare area stretching from the base to a darkened pit in the apical half. Distinctly broader species.


Complex clypeatus cont...
P. occultus

21
21 a. Forefemur with a posterior hair fringe reaching the apex.
b. Forefemur with a posterior hair fringe confined to the basal half.
P. clypeatus
P. ramsarensis
Posted on 20 October, 2022 20:17 by matthewvosper matthewvosper

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