Cordulegaster diadema (Selys, 1868) is found in Costa Rica, Guatemala, seven states in Mexico and three southwestern states in the United States of America. C. diadema occurs in many small populations scattered over a rather large range; the population trend remains unknown. Small populations of C. diadema in the United States appear secure from threats. However, Mexican and Central American populations are poorly known and continuing deforestation of cloud-forest zone could present a threat there in the future. IUCN Red List accessed as Least Concern. This species is thought by most workers to include Cordulegaster godmani, usually considered a distinct subspecies.

This is a apecies of very large size. Body length 76 - 78 mm.  Male abdomen length 58 mm, female abdomen length 61 mm, female hindwing length 52 mm.

Male identification: 
     -  Face dark brown, eyes green and meeting at a point. 
     -  Thorax with two bold yellow stripes. 
     -  Abdomen black with yellow bands and spots. 

Female identification: 
     -  Similar to male. 

The species has accepted subspecies of: 
     -  Cordulegaster diadema diadema (Selys, 1868)  
     -  Cordulegaster diadema godmani (McLachlan, 1878), sometimes as Cordulegaster godmani (McLachlan, 1878) 
 

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