Omus dejeanii

Reiche, 1838

Greater Night-stalking Tiger Beetle

Omus dejeanii is a flightless tiger and the largest in its , measuring 15–20 mm. It inhabits dense coastal forests from British Columbia to northern California. The species is and exhibits exceptionally long mating durations averaging 29.4 hours, far exceeding most other tiger beetles. Males possess enlarged used both for prey capture and for grasping females during prolonged amplexus.

Omus dejeanii by (c) Koji Shiraiwa, some rights reserved (CC BY), uploaded by Koji Shiraiwa. Used under a CC-BY license.

Pronunciation

How to pronounce Omus dejeanii: /ˈo.mus də.ʒe.ˈa.ni/

These audio files are automatically generated. While they are not always 100% accurate, they are a good starting point.

Identification

Distinguished from sympatric Omus audouini by larger body size (scaling factor of 1.3×) and proportionally longer (scaling factor of 1.5×). Geometric morphometric analysis shows interspecific differences in the mandibular region (terebral teeth), likely associated with prey processing. As the largest Omus at 15–20 mm, size alone can be diagnostic where ranges overlap.

Images

Habitat

Dense coastal forests; forest floor in forested areas. Specifically documented from Powell Butte Nature Park, Portland, Oregon in sympatry with O. audouini.

Distribution

Pacific coast of North America from British Columbia south to northern California.

Diet

Predatory; captures and processes prey using .

Behavior

. Exhibits obligatory male-superior mounted mating with average duration of 29.4 (± 5.6) hours—substantially longer than O. audouini and an order of magnitude greater than most other tiger beetles. Males use to grasp females and maintain amplexus throughout copulation. Mating duration is unaffected by time of initiation, food deprivation, or operational sex ratio, suggesting no mate guarding behavior.

Ecological Role

Conspicuous within terrestrial . partitioning with sympatric O. audouini supported by body size and length differences consistent with Hutchinsonian Ratios.

Similar Taxa

Omus audouiniSympatric congeneric distinguished by smaller body size (1.3× smaller), shorter (1.5× shorter), and significantly shorter mating duration.

More Details

Mandible Function

serve dual role in feeding (prey capture/processing) and as secondary sexual organs for grasping females during amplexus, with geometric morphometric differences in the terebral teeth region between .

Reproductive Biology

Syn-copulatory courtship is suggested as the female-choice reproductive mechanism. The extreme mating duration appears to be a -specific trait rather than conditional on environmental or social factors.