Colour Key to the Tribes of the Syrphidae Stuart Ball March 2008
Key to Tribes from Stubbs & Falk, 2002 illustrated with photographs Stuart Ball Introduction Once you are become familiar with hoverflies, you will rarely use the Key to Tribes. Most of the time, you will quickly learn to recognise the main groups and important genera and will go straight to the key to genera in the relevant tribe, or even straight to the key to species for the relevant genus. However, a beginner who has not yet gained this experience, has to start at the beginning and work through the Key to Tribes. This is unfortunate, since this is often the most difficult step! The larger tribes tend to contain a very varied collection of genera and species making it difficult to find a few distinctive characters that neatly sum them up and divide them from all the other groups. Consequently, the Key to Tribes tends to be rather plagued with exceptions some of which can cause the beginner real problems. Matters aren t helped by the fact that the very first couplet (the dreaded hairy humeri ) is not easy! This version of the Key to Tribes from Stubbs & Falk s British Hoverflies has been put together to try and help by illustrating the key features with photographs of specimens, or of hoverflies in the field. Please pay particular attention to the exceptions mentioned in some of the couplets since these try to pick out cases where people particularly struggle. The page numbers referred to in the key relate to the 2 nd edition of Stubbs & Falk published in 2002, the page numbers in earlier editions are not the same. Short cuts Here are some of the groups which are very easy to recognise where you can quickly skip the key to tribes once you have seen and appreciated the relevant features and go straight to the tribe or genus. Large, showy species with a plumose arista Volucella has plumose arista (left) and re-entrant outer cross-vein (right) o If the outer cross-vein is re-entrant then these belong to the tribe Volucellini (single genus Volucella) o Otherwise, they belong to the Sericomyiini (two genera: Arctophila and Sericomyia illustrated in couplet 7 below) Wing with vein R 4+5 strongly looped. This is a nice obvious characteristic of the Eristalini, but also occurs in Merodon (Merodontini). But Merodon is included in the key to genera of the Eristalini, so you can safely go straight to the key to genera (p. 138) for that tribe. 3
Eristalini and the genus Merodon have a strong downward loop in vein R 4+5 Shiny, dark, hump-backed hoverflies with very long antennae belong to the sub-family Microdontinae (single genus Microdon). These are fairly scarce and perhaps more often found as hemispherical armoured larvae in ants nests. Small (6mm) hoverflies with a prominent face and large half-moon shaped antennae with a short and thick terminal arista belong to the Pelecocerini (two genera, Pelecocera on heathland in Southern England from Devon to Surrey and Chamaesyrphus in Pine forest in Scotland). These are all scarce or very rare species. Large, spectacular golden coloured hoverflies with long black antennae with a terminal arista tipped in white belong to the Callicerini (single genus Callicera). The three species are all rare. Microdon Pelecocera Callicera Some of the bigger tribes are reasonably easy to recognise in many cases, but there are exceptions, so you need to check them out fairly carefully: The typical black-and-yellow striped species that you see on flowers in your garden, and that most people will recognises as hoverflies, are usually Syrphini. 4
Pipizini are nearly always rather dark coloured, sometimes with some yellow or orange abdominal markings, but with a rather flat face covered in long downwardly directed hair (which may be pale or dark). The main genus of the Cheilosiini, Cheilosia (the biggest genus in the British fauna with 36 species) all tend to be rather plain looking, black species, sometimes with yellow antennae and/or legs, but otherwise with little or no markings. Cheilosia illustrata, however, does not fit this pattern. It is a very common flower visitor and not very convincing bumble bee mimic. Warning: the common Chrysogastrine Melanogaster hirtella is very easily mistaken for a Cheilosia especially in the male. This tribe is reasonably easy to confirm, when you examine a specimen under a microscope, because of the well developed eye margins ( zygoma ) so make sure you have seen this feature and learned to recognise it. The large tribes, Chrysogastrini and Xylotini, present perhaps the biggest challenge. They contain very diverse genera in which it is rather difficult to point to any feature which places them in a particular tribe. You will probably find that, once you have gained some experience you will recognise many of the genera without really knowing which tribe they belong to. But when you still need to head for the Key to Tribes, then chances are you are dealing with one of these two tribes. 5
Key to tribes 1. Humeri bare [SYRPHINAE]. Head deeply concave so usually sits over and masks the humeri. Humeri hairy [MILESIINAE + MICRODONTINAE]. Head naturally sits well forward so that the humeri are clearly visible. If in doubt, key from here. 14 2 Milesiinae humeri hairy Syrphinae humeri bare, but difficult to see! 2. Upper outer cross-vein re-entrant (i.e. the upper outer cross-vein bends inwards before it meets R 4+5 at an angle of less than 90º, looking from the direction of the wing tip). 3 re-entrant outer cross-vein Upper outer cross-vein not re-entrant. (If the upper outer cross-vein meets R 4+5 at right-angles, as in Neoascia, then it is NOT considered re-entrant). 5 normal outer cross-vein Wing of Neoascia 6
3. Antennae porrect (long, cylindrical, projecting straight in front of head). MICRODONTINAE p. 163 Microdon are very distinctive hoverflies with an unusual hunch-backed appearance. Microdon devius Antennae short. 4 4. Arista plumose. VOLUCELLINI p. 158 Arista bare. Furry bee-like species or with a flat hairy face and swollen hind femur (if not of this description, continue to couplet 5). MERODONTINI p. 147 5. Wing with R 4+5 strongly looped. (Lower and upper outer cross-veins form an almost continuous vein parallel with wing margin). ERISTALINI p. 138 R 4+5 Wing with R 4+5 shallowly dipped or more nearly straight. (If R 4+5 is somewhat dipped, the outer cross-veins are stepped rather than being continuous). 6 6. Antennae porrect (long cylindrical) with terminal arista. CALLICERINI p. 110 The three species of Callicera are all rarities. They are large, golden coloured hoverflies having long antennae with a terminal arista with distinctive white tips. Callicera spinolae Antennae not of this type (if porrect, the arista is dorsal). 7 7
7. Very large broadly built hoverflies with plumose arista. SERICOMYIINI p. 157 Arctophila superbiens Sericomyia silentis Hoverflies without plumose arista (an exception, Hammerschmidtia, is not broadly built and is entirely orange-brown). 8 8. Face flat and entirely covered in long drooping shaggy hairs. PIPIZINI (+Psilota) p. 150 Face not of this type (either not flat or if flat then without an entire covering of shaggy hairs; facial knob often present). 9 9. Wing with inner cross-vein (R-M) before middle of discal cell. (Ferdinandea, with bristles on lateral margin of thoracic dorsum, belongs here). 10 8
Ferdinandea has a brassy coloured abdomen and a light-grey striped thorax. It should key out here but its R-M is just about at the middle of the discal cell. Wing with inner cross-vein (R-M) at or beyond middle of discal cell. (Syritta, with densely grey dusted pleura, belongs here). XYLOTINI p. 158 R-M discal cell Syritta is a small, grey dusted species with swollen hind femora. It should key out here, but its R-M is at about the middle of the discal cell 10. Face concave, without central prominence, but may have a lip just above the mouth edge. CHRYSOGASTRINI (Part) p. 127 Concave face without central prominence projecting mouth edge 9
Face with central prominence (as well as a lip just above the mouth edge) or entire lower part of face projecting forwards (see Pelecocera in next couplet). 11 Rhingia shows the most extreme development of a projecting face Central prominence lip above mouth edge 11. Small species (up to 6 mm long) with face projecting forwards in lower half. Arista shorter than third antennal segment. PELECOCERINI p. 149 Short, thick arista The two genera, Pelecocera and Chamaesyrphus, both have large half-moon shaped third antennal segments. Face projecting forward Face not this shape, or if so then a larger species with arista much longer than third antennal segment. 12 12. Top of abdomen flat at least on tergite 2 and entirely dull on top or with large orange side patches. CHRYSOGASTRINI (Part) p. 127 Abdomen of Myolepta with large orange markings Abdomen flat and dull on top (with shinning margin) Abdomen without above features. 13 10
13. Face with sharply defined and distinct eye margin zone for most of height. Humeri hairy. (The majority of species lack a colour pattern of spots or bars). CHEILOSIINI p. 111 Eye margin typical Cheilosia Melanogaster hirtella (Chrysogastrini) causes lots of people problems, especially in the male, because it is often mistaken for a Cheilosia and keyed out here! It does however have the flat topped, dull abdomen similar to that shown in couplet 12 if you look carefully. It is a small, rather dark species with darkened wings. Face without distinct eye margins, or such a zone only present on lower part of face. Humeri bare. (The majority of species have a distinct colour pattern of spots or bars). 14 [SYRPHINAE] typical Syrphini 14. Face entirely yellow or at least yellow at the sides (only entirely black in some Melangyna, especially M. quadrimaculata, which belong in Syrphini). 15 face yellow at sides 11
Face entirely black. BACCHINI p. 65 15. Antennal third segment modestly elongate. Very small species (up to 5 mm body length). PARAGINI p. 80 Paragus haemorrhous Antennal third segment more compact or extremely elongate. Rarely so small. SYRPHINI p. 81 Chrysotoxum with very elongate antennae typical Syrphini 12