Male, Head: head wide ranging from as wide as thorax to slightly wider; vertex 1/4–1/3 head width; gena 1/3 of head height, approximately 1/2 of eye height; with 1–3 rows of frontal setae; 1–3 of reclinate orbital setae (some species males with proclinate orbital setae present); ocellar setae most often absent, reduced to hair-like in some species; eye bare in all species; parafacial bare and wide, subequal to eye width; fronto-orbital plate ranging from shining silver or gold to brownish with a silver sheen, and displaying varying degrees of hirsuteness, with setulae not typically extending below lowest frontal seta; lower margin of face lower than vibrissa; facial ridge setulose, degree of hirsuteness ranging from halfway along facial ridge to 2/3 of its length; pedicel ranging from orange to black; postpedicel black to black with orange, 2–3X as long as pedicel; arista bare, usually distinctly-thickened on basal 4/5 almost to tip. Thorax: ranging from gold to black, sometimes with light gray to gold tomentum dorsally; four dorsal vittae, these can be thick and unbroken to thin and only scarcely present under certain angles of light; prosternum setose; postpronotum bearing three setae, middle basal seta in line with outer and inner basal setae; anterior margin of anepisternum setulose with long hair-like setulae either ranging from black to yellow or golden brown; chaetotaxy: acrostichal setae 3:3–4; dorsocentral setae 3:4; intra-alar setae 2:3; supra-alar setae 2:3; 3–6 katepisternal setae; scutellum ranging from black to gold tomentose, with 4–6 pairs of long flat marginal setae of subequal length; apical setae when present short often crossed and erect, at a slight upward angle from the plane of the rest of the scutellar marginal setae. Legs: most often black, many examples bearing yellow or reddish ground color, with yellow pulvilli of varying length; hind coxae bare. Anterodorsal row of setae on hind tibia either regular and comblike or irregular and not fringelike. Wing: ranging from pale translucent, to strongly infuscate, to dark gray (almost black); wing vein R₄₊₅ setose, bearing only 2–3 setulae at base; calypters raging from dark gray infuscate to yellowish white. Abdomen: color ranging from grayish–brown to black; abdominal tomentosity ranging from strikingly yellow, often forming conspicuous bands to brilliant white or dull colored, and not forming distinct bands; in some species a narrow median black stripe is present; middorsal depression on syntergite 1+2 (ST1+2) ranging from halfway across tergite to almost reaching to hind margin; median marginal setae present on ST1+2–T5; median discal setae absent on all species; underside of abdomen with sex patch present in some species. Male terminalia: sternite 5 with a deeply excavated median cleft along posterior edge, smoothly U-shaped, margins covered in dense tomentum; posterior lobes rounded apically, either bare, with multiple fine hair-like setulae or with 2–3 strong setae surrounded by many shorter weaker setulae. Anterior plate of sternite 5 subequal to or longer than length of posterior lobes; unsclerotized "window" on anterior plate of sternite 5 ranging from absent to almost entirely transparent directly basal to posterior lobes, the shape of the window as well as its presence varies between species. Epandrium ranging from orange to black and variably hirsute. Cerci in posterior view variable between species ranging between rectangular, digitiform, to triangular, either longer than or only slightly shorter than surstyli; blunt and rounded at apex to apically pointed, either completely separate medially to fused basally along most of their length. Cerci in lateral view, often with a strong anterior curve on apex, giving it a clubbed appearance; cerci densely setose along basal 2/3rds, underside of cerci setose along entire length (visible in lateral profile). Surstylus in lateral view, almost equilateral along its length sometimes ending in a slightly downcurved apex making the structure appear bladelike; surstylus appearing to be separate and not fused with epandrium; when viewed posteriorly surstyli range from slightly divergent, to slightly convergent or bearing inward curved apices but not strongly convergent. Pregonite usually broad, well-developed, apically squared off or rounded, usually blunt, typically devoid of setulae. Postgonite, slightly narrowed, up to 1/3 as wide as pregonite, sharply pointed and curved at apex, typically short and scythelike, with few exceptions where postgonite is subequal in length to pregonite. Distiphallus broadly cone-shaped (in some species this cone or flare is much more pronounced, in others appearing square or barrel shaped), with a slender median longitudinal sclerotized reinforcement on its posterior surface and a broad, anterolateral, sclerotized acrophallus, on anterior surface near apex, ~1.3 times as long as basiphallus.

Female as in male differing in the following traits: Head: bearing two pairs of proclinate orbital setae. Abdomen: often slightly more globose than males; T5 folded over into a narrow slit a trait which is stereotypical of the tribe Goniini. In those cases where sexual dimorphism is observed the differing character states are mentioned in the species description. Sex patch absent in all female specimens.

Belvosia, as in all other Goniini, are difficult to characterize to tribe based on morphological character states but can be reliably ascribed to the tribe (sensu Herting 1984) based on their microtype ovipary. Belvosia are a large, heavy-bodied tachinid, often with brilliant hymenoptera-like abdominal banding in brilliant white or gold. They can be diagnosed based on the following gestalt or combination of traits which can be considered as stereotypical to the group: prosternum setose; males of many species have two pairs of well-developed reclinate fronto-orbital setae (sometimes absent, proclinate in: B.luteola, B.unifasciata, B.fosteri, B.ochriventris, B.slossonae, B.equinoctialis), proclinate in all females; ocellar setae most frequently absent, however can appear reduced and hair-like in some species; eyes bare; facial ridge setose at least over 1/3–1/2 its height; frons distinctively wide in both sexes; parafacial bare; the three major setae of the postpronotum are arranged more or less in a line; usually 4 well developed katepisternals, but numbers can vary between 3–6; three stout postsutural supra-alar setae; abdominal discal setae absent in all species. Previous descriptions of the genus also made mention of the absence of any discernible sex patch in males, however, present evidence suggests that sex patches are in fact present in some species of Belvosia (B.bicincta, B.ciriloumanai, B.duvalierbricenoi, B.freddyquesadai, B.gloriasihezarae, B.guillermopereirai, B.harryramirezi, B.hazelcambroneroae, B.jorgehernandezi, B.josecortezi, B.joseperezi, B.robertoespinozai, B.sergioriosi). Distance between eye and subcranial margin often 1/3 the height of the head. As can be seen in the key to the Tachinidae in Wood and Zumbado 2010, Belvosia can be distinguished from Lespesia Robineau-Desvoidy 1830 which bears the following differences: eye bearing ommatrichia, well developed ocellar setae, and the facial margin arising level with vibrissa. Distinguished from Atacta Schiner by its robust size in addition to Belvosia's presence setulae on facial ridge.

Ubiquitous throughout the New World, inhabiting a wide variety of ecosystems, from southeastern Canada and northeastern USA west to California and south to Argentina and Brazil.

Within the ACG inventory, Belvosia has been reared from the following Lepidoptera hosts throughout the diverse ecosystems of the research area: Erebidae, Eupterotidae, Noctuidae, Notodontidae, Saturniidae, and Sphingidae. Ecological and natural history analysis of the thousands of rearing records will be provided later by the same authors of this work.

Latreillia Robineau-Desvoidy 1830, was proposed concurrently with Belvosia (Robineau-Desvoidy 1830), and originally included 10 species. Eight of the species were from the Old World; four of these are now recognized and are considered synonyms in four different genera (Crosskey 1980, Herting and Dely-Draskovits 1993), and the remaining four are unrecognized Palaearctic species (Herting and Dely-Draskovits 1993). Because Coquillett (1910) designated Muscabifasciata Fabricius, a typical species of Belvosia as now recognized, as type species, Latreillia became a synonym of that name. As Belvosia is restricted to the New World, none of the eight Old World species, including those that are unrecognized, belong to the genus. The tenth included species, Latreilliaunifasciata Robineau-Desvoidy, is another species of Belvosia. Latreillimyia Townsend, a replacement name for Latreillia, automatically becomes a synonym of Belvosia. Triachora Townsend, was proposed by Townsend to include only Latreilliaunifasciata Robineau-Desvoidy. It has been considered as a valid genus distinct from Belvosia by past authors (Sabrosky and Arnaud 1965, Guimarães 1971) for a group of about seven species. It was recently synonymized with Belvosia by Wood (Wood 1987, O’Hara and Wood 1998). Members of this species group are generally smaller than more typical Belvosia, and are not primarily black with yellow-gold abdominal bands, and males have proclinate orbital setae. However, the species exhibit the characters used to define Belvosia above. Goniomima Townsend, was proposed to include only Belvosialuteola Coquillett, and no additional species have ever been placed in the genus. Although it exhibits some apomorphic character states, such as the long setae on the male cerci and the narrowed abdomen similar to that found in some species of Gonia, B.luteola has the character states found in Belvosia and shows features that place it with the species formerly included in Triachora, such as the proclinate orbital setae found in males. Goniomima was synonymized with Triachora by Sabrosky and Arnaud (1965).

The previously described species Belvosiaantillana (Curran 1927b) was only included in a key without any reference to type material and no specimens have been located. We believe Curran was probably referring to Belvosainsularis, described from Puerto Rico in the same year (Curran 1927a), but inadvertantly used a different name. We therefore regard B.antillana as a synonym of B.insularis.

Aldrich (1928) treated Belvosiaanalis (Macquart 1846) as unrecognized within Belvosia; this paper cites the original type material used by Macquart (1846) as originating from Brazil, and presumably destroyed. Aldrich's treatment of this species was based on Macquart's original description where the abdomen was described as "caeruleo-nigro" which Aldrich took to mean as blue, thereby excluding it from the genus Belvosia. The type of Belvosiaanalis sensu Macquart is no longer present in the Paris Museum type list, having since been lost or destroyed. Coquillett later identified material from Mexico as belonging to B.analis. It was on the basis of these specimens that Aldrich conducted his diagnosis and erected the name Belvosiaciliata to include those specimens Coquillet had described. Since the original type material has been lost, the basis for B.analis Macquart cannot be ascertained, we are hereby are treating this species as a nomen dubium.

It is somewhat surprising that the synonymy of B.pollinosa with B.borealis has gone undetected before now. Rowe (1933) clearly noted the multiple median marginal setae on tergites 1+2 and three (i.e., more than a single pair on each segment), a character state only found in B.borealis in the North American fauna. Curran’s "n. sp." label on the holotype of B.pollinosa was presumably added around the time he was working on the genus, before the Aldrich (1928) revision. Rowe was apparently unaware of Aldrich’s paper, as the holotype of B.pollinosa keys easily to B.borealis in Aldrich’s key.

During his long and prolific career D. Monty Wood had occasion to examine Belvosiaflavicauda Riley, at the USNM. The original description cited 5 female syntypes in error, one captured and 4 reared from Mamestraconfigurata Walker, 1856. Careful examination by Dr. Wood, revealed the original captured specimen to be a male, along with 4 reared females. Prior to his passing in 2020, Monty was assisting AJ Fleming in the preparation of this paper where he suggested the inclusion of this male syntype as lectotype. We hereby propose the male syntype as the lectotype of Belvosiaflavicauda by present designation of D. Monty Wood.

After careful examination of the two syntypes of Belvosiaochriventris Wulp, it was determined that they are in fact not conspecific. In his Biologia Centrali Americana, Wulp described the similar characters within the syntypes and then makes mention of additional information pertaining to the syntype originating from Tierra Colorada; further describing the ground coloration of the abdomen and the presence of a dark stripe along its midline. Given the fact that more information was shared about this specimen, we have elected to designate it the lectotype of the species. We consider that the herein designated lectotype of Belvosiaochriventris is in fact conspecific with Belvosialuteola Coquillett and therefore must sink B.luteola as a synonym of the former based on the morphological similarities between the two. The second syntype from Mexico, Guerrero, Amula 6000ft, we hereby designate as a paralectotype. We are not currently able to make a determination on this specimen which at the present time we have chosen to leave as unresolved.