Svastra obliqua expurgata

(Cockerell, 1925)

sunflower bee, long-horned digger bee, female long-horned bee

Svastra obliqua expurgata is a of long-horned bee in the Apidae, native to western North America. It is commonly known as the 'sunflower bee' due to its strong preference for foraging on sunflowers and other members of the Asteraceae family. The has been reclassified taxonomically, with some authorities placing North American species formerly in Svastra into the genus Epimelissodes. It is a solitary, ground-nesting that plays an important role in pollinating native and agricultural plants in its range.

Pronunciation

How to pronounce Svastra obliqua expurgata: /ˈsvastra oˈbliːkwa ɛkspərˈɡɑːta/

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

Identification

Distinguished from similar long-horned bees (Melissodes, Svastra, and related ) by specific morphological characters including details of wing venation, facial markings, and genitalia structure. Identification to level requires expert examination. Distinguished from the green sweet (Agapostemon texanus) by coloration—Svastra lacks the metallic green of Agapostemon. Distinguished from bumble bees (Bombus) by its solitary lifestyle, lack of dense pile, and longer relative to body size.

Appearance

A medium to large-sized with notably long , characteristic of the 'long-horned bee' . Females carry pollen on scopal hairs located on the hind legs, often appearing as dense, brightly colored pollen loads. The body is robust with typical apid coloration. is present, with males and females showing differences in size and antennal length.

Habitat

Found in gardens, arboreta, and natural areas with abundant flowering plants in the Asteraceae . Observed in the UC Davis Arboretum and Public Garden, UC Davis Haven, and similar cultivated landscapes. Requires access to bare or sparsely vegetated ground for nesting, as it is a ground-nesting digger bee.

Distribution

Western North America; recorded from California and surrounding regions. Distribution records indicate presence in Middle America and North America. Specific records from the UC Davis area in California.

Seasonality

Active during late spring through summer and into autumn, with period coinciding with bloom of preferred plants. Observed foraging in June and later months.

Diet

Oligolectic, preferentially collecting pollen from sunflowers (Helianthus) but will forage on a variety of Asteraceae members including purple coneflower (Echinacea purpurea), sneezeweed (Helenium), and related . Nectar is collected from these same plants.

Host Associations

Helianthus (sunflower) - primary pollen sourceStrong preference; derives from this association
Echinacea purpurea (purple coneflower) - pollen and nectar sourceFrequently observed foraging
Helenium (sneezeweed) - pollen and nectar sourceActively foraged in late summer to fall

Life Cycle

Solitary with ground-nesting habit. Females excavate nests in soil, provisioning individual with pollen and nectar for larval development. No communal nesting or social structure. Development includes , larval, pupal, and stages, with likely one per year or partial bivoltinism depending on climate.

Behavior

Forages actively on composite flowers, collecting pollen with hind leg scopae. Exhibits typical solitary with no colony defense. Males likely patrol for females near nesting or foraging areas. Ground-nesting females dig burrows for construction.

Ecological Role

Important of native Asteraceae and agricultural sunflowers. Contributes to plant reproductive success through pollen transfer. As a ground-nesting , it also contributes to soil aeration and nutrient cycling through nest excavation activities.

Human Relevance

Valued as a native in gardens and agricultural settings. Featured in educational materials at UC Davis Haven and similar pollinator education programs. Subject of research on native bee and sunflower pollination. Potential contributor to sunflower crop pollination in agricultural regions.

Similar Taxa

Melissodes agilisAnother long-horned bee with similar and ; distinguished by specific antennal and genitalic characters
Agapostemon texanusGreen sweet found in similar ; distinguished by metallic green coloration and shorter
Bombus vosnesenskiiYellow-faced bumble bee with overlapping range and flower use; distinguished by social colony structure, dense body hair, and shorter

Misconceptions

The 'sweat bee' has been incorrectly applied to this in some photographic captions; true sweat bees belong to Halictidae, while Svastra is in family Apidae.

More Details

Taxonomic Note

This has undergone taxonomic revision. According to research entomologist Tom Zavortink of the Bohart Museum of Entomology, all North American formerly placed in Svastra are now placed in the genus Epimelissodes, making the current name Epimelissodes obliqua expurgata. However, the name Svastra obliqua expurgata remains in widespread use and is accepted in the Catalogue of Life.

Research Significance

Documented in the PBS Deep Look video 'Why Do Sunflowers the Sunrise?' as an example of the specialized relationships that have coevolved with sunflowers. The 's morning foraging activity corresponds with the east-facing orientation of sunflower blooms, demonstrating circadian synchronization between plant and pollinator.