Key to Adult Males and Females of the Genus Megasoma
(female of M. lecontei unknown)
Author: Matthew Robert Moore

1.
 Posterior sternite emarginate at apex (males)
 

1'.

 Posterior sternite rounded at apex (females)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2 (1).
 Elytra with vestiture
 

2'.

 Elytra without vestiture
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
3 (2).
 Anterior tibia arcuate (Fig. 1).
 

3'.

 Anterior tibia straight (Fig. 2).
Fig. 1. M. nogueirai
arcuate foretibia
Fig. 2. M. mars
straight foretibia
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
4 (3).
 Anterior angles of pronotum produced into antero-laterally projecting horns (Fig. 3).
 

4'.

 Anterior angles of pronotum produced into laterally projecting horns (Fig. 4). Southwestern Mexico (Sierra Madre Occidental)
M.
occidentale
Bolívar y Pieltain, Jiménez-Asúa, and Martínez
Fig. 3. M. elephas
pronotum produced into antero-laterally projecting horns
Fig. 4. M. occidentalis
pronotum produced into laterally
projecting horns

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
5 (4).
 Apices of anterior angles (horn) of pronotum curving inward (Fig. 5). Side of elytron, behind humerus with short, recumbent setae. Mexico (southern Sinaloa: Pacific slopes of Sierra Madre Occidental)
M. nogueirai (Morón)
 

5'.

 Apices of anterior angles (horns) of pronotum not curving inward (Fig. 6). Side of elytron, behind humerus velutinous (short, erect setae). Southern Mexico to Venezuela
M. elephas (Fabricius)
Fig. 5. M. nogueirai
apices of pronotal horns curving inwards
Fig. 6. M. elephas
apices of pronotal horns not curving inwards

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
6 (3').
Elytra velutinous (short, erect setae)
 

6'.

 Elytra pilose
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
7 (6).
 Mid-prothoracic horn narrowly emarginate at apex. Anterior angles of pronotum produced into elongate, acute horns (Fig. 7). Brazil
M. gyas Herbst
 

7'.

 Mid-prothoracic horn broadly-bifurcate at apex. Anterior angles of pronotum produced into short, acute horns (Fig. 8). Brazil
M. anubis Chevrolat
Fig. 7. M. gyas
median pronotal horn narrowly emarginate at apex, anterior angles of pronotum produced into elongate, acute horns.

Fig. 8. M. anubis
median pronotal horn broadly-bifurcate at apex, anterior angles of pronotum produced into short, acute horns.

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
8 (6').
 Anterior margin of clypeus with acute, spiniform teeth seperated by 3 tooth widths or more
 

8'.

 Anterior margin of clypeus with acute, spiniform teeth seperated by 1 tooth width or less. Argentina and Paraguay
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
9 (8).
 Pronotum with median, anteriorly directed horn
 

9'.

 Pronotum without median, anteriorly directed horn. Mexico (central Baja California: Cedros Island)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
10 (9).
 Distance between apices of anterior angles (horns) of pronotum nearly twice width of head (Fig. 9). Mexico (southern Baja California)
M. thersites LeConte
 

10'.

 Distance between apices of anterior angles (horns) of pronotum less than 1 1/2 width of head (Fig. 10). Texas and northern Mexico
M. vogti Cartwright
Fig. 9. M. thersites
distance between apices of anterior angles (horns) of pronotum nearly twice width of head
Fig. 10. M. vogti
distance between apices of anterior angles (horns) of pronotum less than 1 1/2 width of head

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  11 (2'). Pronotum with median, anteriorly directed horn. Mexico (Sonora and Sinaloa)
M. pachecoi Cartwright
 

11'.

 Pronotum without median, anteriorly directed horn; anteromedial tubercle or swelling may be present
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  12 (11). Cephalic horn at base on dorsal surface with tooth or process (Fig. 11)
 

12'.

 Cephalic horn at base on dorsal surface without tooth or process (Fig. 12)
Fig. 11. M. mars
cephalic horn at base on dorsal surface with tooth or process
Fig. 12. M. thersites
cephalic horn at base on dorsal surface without tooth or process

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
13 (12). Anterior angles of pronotum produced into acute, anteriorly projecting horns (Fig. 13). Color dull or shiny black. Scutellum on disc rugose. Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Panama, Peru, Suriname, Venezuela
 

13'.

 Anterior angles of pronotum produced into acute, antero-laterally projecting horns (Fig. 14). Color shiny black. Scutellum on disc punctate. Brazil
M. mars Reiche
Fig. 13. M. actaeon
anterior angles of pronotum produced into acute, anteriorly projecting horns
Fig. 14. M. mars
anterior angles of pronotum produced into acute, antero-laterally projecting horns

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
14 (12).
 Pygidium on disc glabrous (some setae basally). Body color black. Southern Arizona
M. punctulatus Cartwright
 

14'.

 Pygidium on disc uniformly setose. Body color reddish-brown.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
15 (14).
Anterior angles of pronotum (horns) with apices rounded. Pronotum lacking median tubercle. Southern California
 

15'.

 Anterior angles of pronotum (horns) with apices spiniform. Pronotum with median, binodose tubercle. Mexico (southern Baja California)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
16 (1').
 Pronotum on disc rugose or rugopunctate.
 

16'.

 Pronotum on disc punctate.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
17 (16).
Elytra with vestiture.
 

17'.

 Elytra without vestiture.

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
18 (17) .
 Scutellum at base rugose.
 

18'.

 Scutellum at base finely punctate.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
19 (18) .
Pronotum with longitudinal, posteromedian carina (Fig. 15). Mexico (southern Sinaloa: Pacific slopes of Sierra Madre Occidental)
 

19'.

 Pronotum without longitudinal, posteromedian carina (Fig. 16).
Fig. 15. M. nogueirai
pronotum with longitudinal, posteromedian carina
Fig. 16. M. elephas
pronotum without longitudinal, posteromedian carina
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
20 (19') .
 Side of elytron, behind humerus velutinous (short, erect setae). Southern Mexico to Venezuela.
M. elephas (Fabricius)
 

20'.

 Side of elytron, behind humerus with short, recumbent setae. Southwestern Mexico (Sierra Madre Occidental)
M. occidentalis Bolívar y Pieltain, Jiménez-Asúa, and Martínez
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
21 (18') .
 Pronotum with longitudinal, posteromedian carina (Fig.17). Brazil.
M. gyas (Herbst)
 

21'.

 Pronotum without longitudinal, posteromedian carina (Fig. 18). Brazil.
M. anubis Chevrolat
Fig. 17. M. gyas
pronotum with longitudinal, posteromedian carina
Fig. 18. M. anubis
pronotum without longitudinal, posteromedian carina
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
22 (17') .
 Frontoclypeal suture with acute tubercle. Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Panama, Peru, Suriname, Venezuela
 

22'.

 Frontoclypeal suture with binodose tubercle. Brazil, Colombia, Paraguay, Uraguay
M. mars Reiche
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
23 (16') .
 Elytra with vestiture.
 

23'.

 Elytra with out vestiture.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  24 (23). Anterior margin of clypeus with acute, spiniform teeth.
 

24'.

 Anterior margin of clypeus with out acute, spiniform teeth. Argentina and Paraguay
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  25 (24). Frontoclypeal suture with transverse, blunt tubercle. Tubercle impressed on top. Mexico (southern Baja California)
M. thersites LeConte
 

25'.

 Frontoclypeal suture with blunt tubercle. Tubercle not impressed on top. Mexico (central Baja California: Cedros Island)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
26 (23'). Frontoclypeal suture with tubercle on distinctly convex, raised surface (Fig. 19). Texas and northeastern Mexico
M. vogti Cartwright
 
26'.


Frontoclypeal suture with tubercle on flat surface (Fig. 20). Southern Arizona, Southern California, Mexico (Sonora and Sinaloa).
Fig. 19. M. vogti
Frontoclypeal suture with tubercle on convex, raised surface
Fig. 20. M. pachecoi
Frontoclypeal suture with tubercle on flat surface
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
27 (26'). Ocular canthus subquadrate with length medially subequal to length distally. Ocular canthus with anterior margin weakly oblique (10 º angle from perpendicular). Southern California
 
27'.


Ocular canthus subtriangular with length medially 1.5 – 2.0 times larger than length distally. Ocular canthus with anterior margin strongly oblique (45 º angle from perpendicular). Southern Arizona or Mexico
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
28 (27') .
 Elytral punctation near base with sparse, small punctures mixed with moderately dense, moderately large punctures (Fig. 21). Mexico (Sonora and Sinaloa)
M. pachecoi Cartwright
 

28'.

 Elytral punctation near base with dense, small punctures mixed with moderately dense, moderately large punctures (Fig. 22). Southern Arizona
M. punctulatus Cartwright
Fig. 17. M. pachecoi
elytral punctation
Fig. 22. M. punctulatus
elytral punctation