|   
   
    | 1. Tarsi 5 segmented, pretarsus with pair of strong claws . . . . . . . . . . .
    . . . . . . . . . . . . . . . . . . . . . .  |    
   
    | —. Tarsi 2–5 segmented; pretarsus with neither claws nor sensory spots; or tarsi 5-segmented and pretarsus with a pair of very weak claws, or a single
    claw and with sensory spots . . . . . . . . . . . . . .  |    
   
    | 2(1). Antenna 8 segmented; mandibles large and robust, triangular shaped,with broad
    base and of generalized chewing structure. . . . . . . . . . . . . . . . .
    . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
    . . .  |    
   
    | —. Antenna 6–7 segmented; mandibles, if present, small, narrow, and
    bladelike.. . . . . . . . . . . . . . .  |    
   
    | 3(2). Galeal lobe
    at base of maxillary palp present  .
    . . . . . . . . . . . . . . . . . . . . .. 
    Protoxenidae |    
   
    | —. Galeal lobe at base of maxillary palp absent .  . . . . . . . . . . . . . . . . . . . .
    . . . . . . . . . . . . . . . . . . .  |    
   
    | 4(3).
    Protrochanter and profemur free   . .
    . . . . . . . . . . . . . . . . . . . . . . . .  Cretostylopidae, n. fam. |    
   
    | —. Protrochanter and profemur fused (Host: unknown)   . . . . . . . . . . . . . . . . . . Bahiaxenidae |    
   
    | 5(2). Prementum
    free, with short palps; hind wing CuA1 short, extending about to middle of wing; front
    branch of MA absent; antenna 7- segmented, with
    flabella on antennomeres III and IV  . . . . . . . . . . . . . . .
    . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
    . . . . . . . . . . . . . . . .Mengeidae |    
   
    | —. Prementum fused to hypopharynx; hind wing CuA1 extending almost to edge of wing; MA strongly
    developed with anterior branch; antenna 6- segmented, with flabella on antennomeres III to IV or III to V
    (Host: Zygentoma: Lepismatidae)  . .
    . . . . . . . . . . . . . . . . . . . Mengenillidae |    
   
    | 6(1). Mandibles absent; tarsi 4–5 segmented, pretarsus with a pair of claws, or a
    single claw, or tarsi 4 segmented and pretarsus
    without claws; antenna 5–7 segmented, with flabella on antennomeres III–IV or III–V (Host:
    Hemiptera: Cydnidae, Blissidae, Pentatomidae, Lygaeidae, Coreidae) (also
    known from fossils)   . . . . . . .
    . . . . . . . .  . . . . . . . . . .
    . . . . . . . . . . . . . . . .  . .
    . . . . . . . . Corioxenidae |    
   
    | —. Mandibles present, narrow and blade-like; tarsi 2–4 segmented, pretarsus without claws; antenna 4–7 segmented, with flabella on antennomeres only on
    III or IV, or III & IV, or III to V, or III, V, & VI, or III to VI. . . . . . . . . . . . . . . . . . . .
    . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  |    
   
    | 7(6). Tarsi 3 segmented (Host: Hemiptera: Cercopidae, Cicadellidae, Coreidae,
    Delphacidae, urybrachyidae, Flatidae, Fulgoridae, Issidae, embracidae,
    Pentatomidae, Tettigometridae; Diptera: Tephritidae; rthoptera:
    Tridactylidae; Blattaria: Blattellidae)   
    . . . . . . . . . Halictophagidae |    
   
    | —. Tarsi 2 or 4 segmented. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
    . . . . . . . . . . . . . . . . . . . . . . . . . . . .  |    
   
    | 8(7). Tarsi 2 segmented; antenna 4 segmented
    (Host: Hemiptera: Delphacidae, 
    Dictyopharidae Eurybrachidae, Flatidae, Fulgoridae, Ricaniidae)   . . . . . . . . . . . . . . . . . . . .
    . . . . . Elenchidae |    
   
    | —. Tarsi 4 segmented;
    antenna 5–7 segmented . . . . . . . . . . . . . . . . . . . . .  . . . . . . . . . . . . . . . . . . .  |    
   
    | 9(8). Antennae 7 segmented, with flabella on antennomeres III, V, and VI; maxillary
    base five times longer than palpus (Host: unknown) (also known from
    fossils)   . . . . . . . . . . . . .
    . . . Bohartillidae |    
   
    | —. Antennae 4–7 segmented, with flabellum on antennomere IIII
    only; maxillary base equal to, or smaller than palpus . . . . . . . . . . .
    . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
    . . . . . . . . . . . . . .  |    
   
    | 10(9). Antenna 4 or 6 segmented,
    with flattened flabella . . . . . . . . . . . . . . . . . . . . . . . . . .
    . . . .  |    
   
    | —. Antenna 7 segmented,
    with rounded flabella . . . . . . . . . . . . . . . . . . . . . . . . . . .
    . . . . . . . . . . .  |    
   
    | 11(10). Antenna 6 segmented, metathorax
    with spoon-shaped sclerite (Host: Hymenoptera: Andrenidae, Colletidae,
    Halictidae) (also known from fossils)  
    . . . . . . . . . . . . . . . . . . Stylopidae |    
   
    | —. Antenna 4 segmented,
    metathorax with no spoon-shaped sclerite (Host: Hymenoptera: Masaridae,
    Mutillidae, Sphecidae, Vespidae)  .
    . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Xenidae |      
   
    | —. Wing venation with only CuA1 (Host: Males – Hymenoptera: Formicidae:
    Dolichoderinae, Ecitoninae, Formicinae, Myrmicinae, Pseudomyrmecinae,
    Ponerinae / Females – Orthoptera, Mantodea) (also known from fossils) . . .
    . . . . . . . . . . . . . . . . . . . . . . . . . . Myrmecolacidae |    = = = = = = = = = = = = = = =  Reference:   Kathirithamby, J. and M. S. Engel.  2014.  A revised key to the living and fossil
  families of Strepsiptera, with the description of a new family, Cretostylopidae.  J. Kansas Entomol. Soc. 87(4):  385-388.   - - - - - - - - - - - - - - - - - -
  - - Note:  Bohart noted Lychnocolacidae may not be a valid family. |