- bristle (seta/setae): a bristle is a stout hair with a socket at the base, allowing the bristle to articulate.
- hair: these are fine, (usually) flexible and emerge from the integument without a socket at the base. As such their orientation never changes.
- dusting: also called pollinosity, this is the grey, powdery, scaley surface covering that forms patterns like stripes or bands across the whole body. It is important to assess the extent of dusting and this is best viewed from above and behind (postero-dorsally) under an even, white light.
For help making identifications and for some of the technical language used in keys see my other article on Identifying Insects.
The head contains a lot of the most important keying features so if your specimen has lost its head then you are going to really struggle for an ID … consider binning it and saving yourself a lot of trouble!
- arista: the hair-like organ attached near the top of antennal segment 3. Very important in tachinid classification – you will need to know whether it is plumose (with side filaments, like a feather – lots of Dexiinae); haired (hairs longer than the maximum width of the arists – quite rare); or bare (the most common state – the arista might still have some small hairs but these are not counted). The arista is 3-segmented and in most taxa the basal 2 segments are tiny but in some genera (e.g. Triarthria, Germaria etc.) segments 1 & 2 are elongate. The arista is thicker at the base than the apex and where the arista starts to taper is significant when keying some taxa.
- antenna, flagellomere: divided into 3 segments, with the basal cup (scape) and then segment-2 (pedicel), which can bear a single long hair in Dexiinae and be variously coloured in other key-tests, and the most important bit – segment-3. The shape, length and colour of segment-3 is important to assess. Beware that some keys number the segments from basal to apical and others from apical to basal.
- mouth-edge: whether or not the anterior edge of the mouth protrudes beyond the base of the vibrissae or not is an important test and can be tricky to assess in some specimens. If you are dealing with material from alcohol beware of shriveled specimens where the face bows out or is creased unnaturally. Most cases with protruding mouth edge (Linnaemya / Panzeria / Eriothrix etc.) would be very obvious but some cases are more 50/50. If in doubt view the mouth edge from underneath (ventrally) because this often gives the best perspective – and then the mouth edge should obviously protrude – not just clip a line between the vibrissae. So on marginal specimens choose ‘not protruding’.
- eyes: the commonest key-test is to see whether the eyes are hairy or bare. Hairy eyes are usually densely hairy (as in Linnaemya, Phryxe etc.) or the hairs will at least be longer than 3 eye facets. If the eye has only a few scattered, short hairs then call it bare. Beware of rubbed specimens from malaise traps where the hairs have been washed off. If you have old or worn specimens then look closely at the lower quarter against a dark background.
- ocellar triangle (ocelli): this is a triangular group of little round light-sensory ‘eyes’ on the top of the head – present in most genera, except Drino. There are 2 posterior ocelli and 1 anterrior ocellus.
- ocellar bristles: 2 bristles that usually emerge from in front of the posterior ocelli and just behind and to the sides of the anterior ocellus. It is important to ascertain whether they are proclinate (pointing forwards), reclinate (pointing backwards) or lateroclinate (pointing outwards). Proclinate is by far the commonest configuration.
- frons: the area of the top of the head between the eyes and extending forward to the base of the antennae and back to the vertical bristles. You will often be asked to measure the width of the frons in relation to the width of one eye when viewed from above (dorsally) or (rarely) compared to the width of the posterior ocelli. Occasionally (e.g. in Siphona and Cylindromyia) you will be asked to measure the forward depth compared to the length of the antennae. Thsi is always taken from the base of the antennae (pedicel) to the vertical bristles.
- frontal stripe: the central stripe running from the base of the antennae to the vertical bristles – usually much darker than the surrounding areas.
- parafrontal area (parafrontalia): this is the area between the frontal stripe and the eye margin. This area usually has arrangements of bristles which are important.
- frontal bristles: the bristles that border the frontal stripe and usually curve inwards, almost touching their opposite number.
- parafrontal bristles: the bristles that are positioned between the frontals and the eye margin. You will be asked to check how many upper ones are reclinate – usually there will be at least 2 but occasionally there is just 1 on each side.
- outer orbitals: these are the parafrontals (usually 1 or 2 pairs and proclinate) located between the base of the antennae and the the margin. These are primarily a feature of female tachinids – males usually do not have them.
- inner orbitals: these are the parafrontals that are located higher on the parafacialia and are usually slightly reclinate.
- vertical bristles: there are usually a pair each of inner and outer vertical bristles located dorsally at the dorsal posterior corner of each eye. If in doubt locate the single row of occular bristles that runs just behind the eyes just as the back of the head falls away behind the eyes. The verticals are locate in line with these at the top of the head and are usually obviously larger than the occulars … if you can’t see any strong bristles that are clearly bigger than the occulars (or at the very least the sockets for them) then it doesn’t have them. Occasionally a species will have inner verticals but no outer verticals (e.g. Panzeria).
- occular bristles: this is a single row of bristles that runs behind each eye demarking the area where the back of the head starts. This row is seldom tested but you locate other features (such as the verticals or scattered black hairs on the back of the head) in relation to the occulars.
- facial area (face): this is the (usually sunken) area behind the antennae and between the base of the antennae and the anterior mouth edge. In some dexiines there is a central facial ridge but other than that this area is seldom tested.
- facial ridge: this is the slightly raised area between the face and the parafacialia, running from the vibrissae up to the base of the antennae. The presence and extent of bristles on this ridge is a very important feature.
- vibrissae: a pair of bristles that mark the lower corners of the face, at the base of the facial ridges. These are usually obvious as they will be the longest, stoutest bristles in this area – pointing forwards and curving in towards each other.
- parafacial area (parafacialia) (the ‘cheeks’): this is the region between the facial ridge and the inner eye margin. Vertically it extends from the base of the eye up to the lowest frontal bristle. This is a distinction that often confuses beginners but if a row of bristles extends down from the frontal area then they are all still frontals, even if they are technically on the parafacial area … and the parafacial area is shortened to the part below where these bristles finish. The only exception is when the parafacial is entirely or partly bristled itself but the key should explain what to look for if there is any confusion. Often you will be asked to check for hairs on the parafacials and this means any small hairs below the lowest parafrontal bristle.
- gena or peristome (the ‘jowls’): the region below the lower, ventral eye margin. The main test that you will be asked to make is to view the head laterally and measure the height of the gena in comparison to the height of the eye. In some species the colour and thickness of hairs & bristles on the gena is also important.
- Peleteria bristles: these are stout bristles that, in Europe, only occur on the genus Peleteria but do occur in new-world Tachinini. They are found on the parafacial between the lower eye margin and the vibrissae.
- proboscis: the proboscis is usually quite inconspicuous and sits under the head in the mouth. The main, rigid part of the proboscis is called the haustellum and occasionally you will be asked to compare its length to its width. In genera like Prosena & Aphria the proboscis is long and points forwards under the head, while in Siphona it is double-hinged – the haustellum comes forward and then the proboscis bends back and down. In Siphona you will be asked to measure the length of the haustellum in relation to the height of the head.
- palps (palpi): the palps are 2 sensory organs located near the top/base of the haustellum. The colour is usually black or dark brown but occasionally yellow. The shape of the palps can be long and thin (filiform) or with broad tips (spatulate). Rarely palps can be completely absent or reduced to tiny buds.
- back of the head (occiput): the colour of hairs on the back of the head is important too. You will be asked to check for whether the hairs are black or pale on the dorsal region of the back of the head – usually there are a mixture of both but on some genera they are all black (e.g. Macquartia) or all white (e.g. Exorista).
The thorax is a highly complex and very important area for keying features. The features are spread evenly on all 4 surfaces so I like to pin specimens laterally with the wings at about 45-degrees to the upper/lateral faces. In this orientation only 1 lateral face is obscured and everything is very visible. It also allows for easy micro-pinning of the genitalia and easier arrangement of legs.
- postpronotal lobe, postpronotum or humeral callus (the ‘shoulders’): this raised and rounded area contains an important arrangement of bristles that can be tricky for novices to interpret. You are usually asked to see of the largest bristles for a roughly equilateral triangle or a straight line. The key is to observe the area from above with the head pointing away from you and the most basal bristles should be the largest.
- suture: all calyptrates have a grove or suture that runs across the thorax just ahead of the wing bases, dividing the thorax into an anterior third and a posterior 2 thirds. When counting the number of bristles they are always quoted as pre- or post-sutural.
- dorsal bristles: the number of bristles in each longitudinal row on the dorsum is very important in the keys. Be careful to check each side because occasionally the rows will not be entirely symmetrical. The lines of bristles each have names, so starting with the center line and workign outwards we have: acrostichals, dorsocentrals, intra-alars & supra-alars.
- scutellum: the scutellar bristles are very important for tachinid classification but they are often missing or disturbed in some way.
- apical scutellars: usually crossed but occasionally absent, parallel or diverging. Often the apicals are raised relative to the horizontal.
- subapical scutellars: usually long and diverging – only converging in groups like Siphonini.
- lateral scutellars:
- basal scutellars:
- subscutellum: the bulge just under the scutellum that almost all tachinids possess. It should be fully-rounded and fairly visible, especially laterally, but do not confuse it with the rounded part of the back of the thorax which curves down to the abdomen.
- notopleural bristles: the notopleuron is a small rectangle located between the humeral callus and the wing base, usually with 2 moderately stout bristles on it. The length of these is often compared to the pre-alar (the most anterior post-sutural supra-alar bristle) or the first intra-alar or dorsocentral.
- katepisternum (sternopleuron): a large shield-shaped area on the side of the thorax, below the wing, arising between the fore and mid coxae and extending above the middle leg. The katepisternum has an arrangement of stout bristles that are very important for determining tachinids.
- pteropleuron (anepimeron): the section of the thorax under the wing, above the katepisternum. This is usually covered in small hairs and fine bristles – and in some species a large, curved bristle called the pteropleural bristle.
- prosternum: a small chitinous patch anterior to an between the fore coxae, often bearing small hairs but occasionally bare. This is an important taxonomic feature but it can be hidden if you pin your specimens with the head down and the fore legs held forwards. If specimens are pinned laterally I have found that the prosternum is usually visible.
- proepisternum or propleuron: a small area in front of the first spiracle and below the humeral callus. Usually bare but occasionally with small black hairs in genera like Meigenia and some of the Dexiinae.
- hypopleural bristles: these should be present in all tachinids – a fan-like arrangement of bristle anterior to the hind spiracle.
- spiracles: the only spiracle of real note when keying is the hind, which is usually covered by a round flap which attaches anteriorly, but can have 2 equal-size lappets in some unusual groups, like the Polideini (Lypha & Lydina).
- katepimeron or barette: a small strip between the katepisternum and the hind spiracle – often quite difficult to see and you need to be able to determine whether it has any small black hairs on it.
- pteropleural bristle: located under the wing and curving backwards, above the katepisternum. When present the pteropleural bristle is sometimes quite large.
- post metacoxal area: this area is between the hind coxae and the underside of the abdomen. Most often membranous, it can be sclerotised with transverse wrinkles in some phasiine groups.
- calyptrae (squamae): the upper and lower calyptrae (from where the calyptrate flies get their name) are usually white or yellow rounded flaps located just behind the wing bases, next to the scutellum. These usually touch the sides of the scutellum but in some species they diverge away from the scutellum (some Macquartia spp. and Rhinophoridae); have a rolled-over (‘balloon-like’) edge (e.g. Winthemia); or have dorsal hairs (Nemoraea pellucida).
- subcostal (sc): a short, stubby vein – the first to touch the costa. Rarely checked for anything.
- r1: the first radial vein that is regularly checked – usually dorsally for bristles but occasionally the check refers to the ventral surface.
- r2+3: this radial vein touches the wing margin between r1 and r4+5.
- r4+5: vein r4+5 is most often referred to when checking whether it has hairs along its length or extending beyond cross-vein r-m, which joins it to the median vein.
- median (m): this is one of the most important veins on the wing for features. The vein usually features a bend as it changes direction to meet the wing margin anteriorly. The shape of this bend and the relative lengths of the sections are very important.
- r-m: a short cross-vein that links r4+5 with the median vein.
- m-cu: a slightly longer cross-vein that links the median vein with the cubital. m-cu is usually slightly sinuous and more or less perpendicular to the median vein but can (in Voriini) be steeply angled in relation to the median vein. You will also be asked to check how far along the median vein it is attacjed – in relation to r-m and the bend in the median.
- cubital (cu): this vein is located between the median and anal veins. It very rarely touches the wing edge and is most often checked for hairs in the Siphonini.
- anal vein: rarely checked but this is the most posterior and weakest vein on the wing. When measuring how far it reaches be careful not to include the create in the wing that usually extends from it to the wing margin.
- costa: the leading edge of the wing, with a highly reinforced vein covered with tiny little bristlets. The wing edge is divided into sections marked by where the radial veins meet the edge. The underside of section 2 is usually bare between the bristlets on the leading edge and the wing membrane itself, but can have some scattered tiny bristlets in this usually bare area.
- tegula: this is a disc-like flap at the very base of the wing, close to the basicosta.
- basicosta: the unbristled basal section of the wing, next to the tegula.
- wing sections: the radial veins all touch the wing edge at different places and the distance between where each vein touches is sometimes useful for determining different species. The relative lengths of the sections is best measured using a graticule, remembering that the tip of the wing is often considered to be a break between 2 sections.
- costal spine: A single bristle emerging from where the subcosta touches the wing edge – usually much larger than any of the costal bristlets.
- node of r4+5: this is a chitinous lump, located quite close to the base of the wing which nearly always has hairs on it. r2+3 and r4+5 emanate from this node and it is from here that we measure the extent of hairs along r4+5.
- petiole: r4+5 and the median vein most often reach the wing margin independently but in some taxa the median vein bends up to meet r4+5 which then extends to the wing edge in a stalk, called the petiole. The petiole can be long (e.g. Wagneriini) or very short – veins r4+5 and m meeting at the wing edge.
- appendix: the median vein often bends and the bend is usually unornamented but can feature an extension running in the same direction as the median vein before the bend, called an appendix. Don’t confuse this with the crease, present in Exoristini.
- haltere: the small spoon-shaped organ that replaces the hind wing in all dipterans. The haltera is only ever tested for colour – usually black/brown but occasionally pale in some taxa.
- microtrichia: these are microscopic hairs on the wing membrane itself – occasionally you will be asked to check for their extent in certain areas, such as around sc and r1.
It is very important that you familiarise yourself with the way that the leg is oriented because it is a cylindrical surface with dorsal, vertical, anterior and posterior faces – each of which might carry an important bristle to check for. The key is to first check for the dorsal face where you should see a ridge marked by 2 clear and distinct rows of short bristlets – the opposite of this will be the ventral face. Then consider how the leg is articulated on the body and the face looking forward will be anterior and the one looking backwards will be posterior.
- coxae: the coxae are the segment closest (most proximal) to the body and are usually quite small. The main tests are usually just colour but the hind coxae occasionally have from 1-5 hairs on the inner posterior surface in genera such as Carcelia & Huebneria. This is often quite a difficult feature to check so try to set your specimens with the abdomen horizontal, not hanging down, and the hind legs partially extended.
- femur (the ‘thighs’): this is generally only checked for colour.
- tibia (the ‘shins’): these bear several important bristles, most notable the postero- and antero-ventral pre-apical spurs. You should be looking at the underside of the leg, at the end of the tibia where you should see 2 fairly small but obvious bristles. The hind tibia also features some bristles in the middle, which are used in the genus Cylindromyia and on Sturmia you are asked to check for the ‘comb’ of bristles that runs along the antero-dorsal surface. The fore-tibiae also feature antero-dorsal and dorsal pre-apical spurs that need to be compared in some keys.
- tarsi (the ‘foot’): a 5-segmented portion of the leg, which is usually easy to spot. You are often asked to compare the relative sizes of the segments, either to the length of the claws or to each other. The segment closest to the tibia is often called the basitarsus.
- claws & pulvilli: The claws are most often checked for length in comparison to the nearest (5th) tarsal segment. Be careful though because on worn specimens the claws might be broken. Also note that the claws are often the quickest and easiest way to check the sex of an individual – long claws (e.g. longer or nearly as long as the 5th tarsal segment) suggest a male, while short claws (e.g. much shorter than the 5th tarsus) suggest a female. This is particularly useful in the Phasiinae where the males and females sometimes have very similar-looking genitalia.
The abdomen is divided into transverse segments, numbered starting at those closest to the thorax. The segments have paired dorsal and ventral panels called tergites and sternites, respectively – though in tachinids we rarely consider the sternites because they are tiny and usually hidden by the corresponding tergite that wraps around the abdomen and touches on the ventral side.
- T1+2 or syntergite 1+2: this is the dorsal abdominal segment closest to the thorax, which often has an excavation that the scutellum rests in and a pair of dorsal marginal bristles. The unusual numbering of this segment is due to the fact that actually T1 is so small that it is very hard to see, so it is nearly always lumped together with T2.
- T3,T4,T5: the other dorsal abdominal segments, which often bear dusting and dorsal or marginal bristles, which all need to be checked. Dusting is best viewed under a string, flat, white light and by holding the specimen so that you are looking from a dorso-posterior position (above and behind).
- the excavation: the dent or excavation in T1+2 is usually large enough that it reaches back to the posterior margin of T1+2. But on some taxa the excavation stops short of the margin and this can be quite an important feature to look for.
- marginal bristles: the commonest marginals that need checking are the dorsals but occasionally you will be asked to check for laterals or count how many bristles there are in the marginal row. Marginals usually occur very close to the margin but in some taxa (rarely) they can occur quite anterior to the tergite and in this case the marginals are the bristles that are closest to the margin. There are no species (to my knowledge) that have discals but no marginals.
- discal bristles: the discal bristles are located anterior to the marginals and usually we only refer to the median (uppermost) bristles.
- sternites: the sternites are very rarely considered in tachinids but in some species you will be asked to check the colour of the hairs on sternite 1. Beware that most often features that are on the ventral side of the abdomen still refer to the tergites, not the sternites, which in most species are always tiny and hidden by the overlapping tergites.
- male genitalia (post abdomen): these are often very important features for determining species. In many cases it is possible to make a determination without them but with the genitalia to back it up the determination is much more positive. The genitalia do not usually need any special preparation – just make sure that they have bene folded out and pinned while the specimen dries – then they will be visible enough. The main parts form a forward pointing 3 or 4-part structure with a central element made from 2 parts called cersi and on each side the surstyli. Between the cerci and surstyli is a filamentous structure with chitinous segments called the epandrium. The epandrium is very seldom checked in tachinids but the ventral and lateral shapes of the cerci and surstyli is very important.
(photographs (c) Dave Dare & Malcolm Storey)