Omus audouini

Reiche, 1838

Audouin's Night-stalking Tiger Beetle

Omus audouini, commonly known as Audouin's Night-stalking Tiger , is a tiger beetle in the . It exhibits pronounced sexual size dimorphism with females larger than males, and possesses that serve dual functions for prey capture and mating amplexus. The species shows partitioning with sympatric O. dejeanii through body size and mandible length differences following Hutchinsonian Ratios. It is of conservation concern in Canada due to its extremely limited distribution.

Pronunciation

How to pronounce Omus audouini: /ˈoʊ.məs ɔːˈduː.ɪ.naɪ/

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Identification

Distinguished from sympatric O. dejeanii by body size (approximately 1.3x scaling ratio) and length (1.5x scaling ratio). The region of the mandibles (terebral teeth) shows -specific differences related to prey processing, while the region is sexually dimorphic. In Canada, the only other Omus species is O. dejeanii, making identification relatively straightforward where ranges overlap. Presence can be indicated by Douglas aster (Symphyotrichum subspicatum) in upper salt marsh at Boundary Bay.

Habitat

Forest floor in forested areas; upper salt marsh habitat in southwestern British Columbia specifically associated with plant 15 m from flood-protection dikes dominated by Douglas aster (Symphyotrichum subspicatum). Habitat transitions from diverse near dikes to halophyte-dominated estuarine marsh at greater distances.

Distribution

West coast of North America; in the United States found along the west coast, while in Canada it is extremely limited to Boundary Bay and a small patch along the coast of Victoria Island in southwestern British Columbia. The Canadian represents a significant range disjunction and conservation concern.

Seasonality

Nocturnally active as . Specific seasonal activity period not well documented in available sources, though night-stalking tiger beetles are typically active during warmer months.

Diet

Prey captured and processed using ; the mandible region (terebral teeth) is specifically associated with prey processing. Specific prey items have not been identified in available literature.

Life Cycle

Larval presumably similar to other Omus , with larvae creating burrows in soil. Detailed information including developmental duration and instar number not available in provided sources.

Behavior

with conspicuous role in terrestrial . Mating involves male-superior mounted position with notably extended duration averaging 10.6±1.8 hours—an order of magnitude greater than other tiger beetles. Males use to grasp females and maintain amplexus during mating. Syn-copulatory courtship has been proposed as a female-choice mechanism. Time of initiation, food deprivation, and operational sex ratio do not significantly affect mating duration in laboratory conditions.

Ecological Role

within terrestrial . The ' activity pattern suggests it occupies a distinct temporal from tiger beetles.

Human Relevance

of conservation concern in Canada due to extremely limited distribution. associations with Douglas aster (Symphyotrichum subspicatum) have been used to develop survey methods for locating previously unknown and mapping potential habitat. Subject of ecological research on partitioning and .

Similar Taxa

Omus dejeaniiSympatric at Powell Butte Nature Park, Portland, Oregon; distinguished by body size (1.3x ratio) and length (1.5x ratio) following Hutchinsonian Ratios; mandible region differs in structure
Other Omus speciesApproximately 9-10 in Omus in western North America; O. audouini distinguished by geographic distribution and morphometric ratios where sympatric

More Details

Geometric Morphometrics

Geometric morphometric analysis has demonstrated that shape differs between sexes and in complex ways: the mandible region is sexually dimorphic, while the region (terebral teeth) shows interspecific differences linked to prey processing.

Conservation Status

In Canada, the is considered at risk due to its extremely limited distribution restricted to upper salt marsh at Boundary Bay and a small area on Victoria Island. The strong association with Douglas aster (Symphyotrichum subspicatum) provides a tool for habitat mapping and surveys.

Mating System

The exceptionally long mating duration (10.6±1.8 hours average) distinguishes this from most other tiger beetles. The serve a secondary sexual function in addition to feeding, being used by males to grasp and maintain hold on females during amplexus.