The Inexplicable Mojo of Tiger Beetles.A Case forCicindelidia senilis frosti Varas-Arangua:Taxonomic Status, Habitat Preferences, Seasonality.

The halophilic tiger beetle, Cicindelidia senilis frosti Varas-Arangua, has been the subject of some debate concerning its taxonomic status as a valid subspecies or merely a color form of the nominate Cicindelidia senilis senilis G.H. Horn.

The two subspecies have been distinguished on the basis of dorsal coloration and distribution: C. senilis senilis, brown to blackish-brown from northern California (San Francisco Bay area to Solano and Sonoma Counties, a disjunct inland population at Carrizo Plain, San Luis Obispo County) and C. senilis frosti, greenish to greenish-brown (rarely bluish), from coastal southern California (San Diego to Ventura and Santa Barbara Counties, a disjunct inland population at Lake Elsinore, Riverside County). Much of the historical distribution of the latter subspecies has been fragmented into isolated populations because of cumulative habitat degradation.

Cicindelidia senilis senilis G.H. Horn
San Franciso Bay, California

Cicindelidia senilis frosti Varas-Arangua
Syntype Male
California Academy of Sciences #8149

                             

Cicindelidia senilis frosti: Labels of Holotype
California Academy of Sciences

When present, the subspecies, C. senilis frosti, occurs in areas of tidal salt marshes and associated salt pans and mudflats. Though more of the exception than the rule, it has also been encountered along the damp/dry sand beach interface. At the turn of the 20th century, when  the type specimen was collected (note type labels, left), Manhattan Beach was an area of wind-swept sand dunes and salt marshes which correspond to the subspecies' ecology. Needless to say, this population has been extirpated. Of the several specimens I have examined, none have approached the distinctive blue-green dorsal coloration of the type. Recently collected specimens are more of a muddy green.

Manhattan Beach, Los Angeles County.
C. 1910

Collection records indicate C. senilis frosti is a spring-fall species but may also be active during summer. Two specimens in my collection from Ventura County were collected in mid-July.

Internet Resources

Cicindelidia senilis senilis image courtesy of Bugguide. C. senilis frosti images courtesy of California Academy of Sciences Research Archive. Period Manhattan Beach photo courtesy of Maureen McGowan.

                                           © Delbert La Rue 2012. All Rights Reserved.