Syrphus opinator

Syrphus opinator can be distinguished from bees and wasps by its single pair of wings, very short antennae, and hovering flight capability. Bees have two pairs of wings and longer, often elbowed antennae. From other syrphid genera, Syrphus species can be recognized by specific wing venation and abdominal patterning, though precise identification to species level often requires examination of subtle morphological features. The black-margined wing pattern helps distinguish this species from some congeners.

Adults resemble wasps or bees with a black and yellow color pattern. The common name "black-margined flower fly" refers to dark markings along the wing margins. Males have eyes that meet at the top of the head; in females, the eyes nearly meet. The species possesses the short antennae typical of syrphid flies. Adults have only one pair of wings, distinguishing them from the two pairs found in bees and wasps. The mouthpart is an extendable proboscis tipped with a sponge-like pad, retracted under the head when not in use.

Found in gardens, meadows, and other habitats with flowering plants and aphid populations. Observed in the Ruth Risdon Storer Garden at UC Davis and the Greater Yellowstone Ecosystem. Associated with environments supporting both nectar sources for adults and aphid colonies for larval development.

Western North America. Documented in California (including UC Davis Arboretum) and the Greater Yellowstone Ecosystem (Montana, Wyoming, Idaho). iNaturalist observations suggest broader distribution in western North America.

Adults are especially conspicuous in spring and fall when aphid populations peak. Active year-round in mild climates; observed in January in California.

Larvae are aphid predators. Adults feed on nectar and pollen from flowers.

Females lay eggs in or near aphid colonies. Larvae pass through three instars, feeding on aphids, before pupating. The pupa is a convex, pear-shaped structure attached to leaves, stems, or other substrates. Adults emerge from the pupal case.

Adults exhibit hovering flight, a characteristic behavior of syrphid flies. They visit flowers for nectar and pollen, serving as pollinators. Adults warm flight muscles by basking before activity.

Larvae function as biological control agents of aphids, reducing pest populations in gardens and agricultural systems. Adults contribute to pollination of various flowering plants.

Beneficial insect in gardens and agriculture. Larval predation on aphids provides natural pest control, potentially reducing need for chemical interventions. Frequently mistaken for bees or wasps, leading to unnecessary concern; education needed to promote recognition and conservation.

• Honey bees (Apis mellifera)Similar size, coloration, and flower-visiting behavior, but bees have two pairs of wings, longer elbowed antennae, and cannot hover persistently
• Other Syrphus speciesClose morphological similarity requiring detailed examination of abdominal patterning and wing markings for definitive identification
• Allograpta speciesSimilar appearance and behavior as flower flies, but differ in body proportions and abdominal patterning

Adults are commonly mistaken for honey bees or wasps due to mimicry. Larvae are often overlooked or mistaken for caterpillars or other herbivores; they may be inadvertently killed during aphid control efforts by gardeners unaware of their beneficial predatory role.

• hover fly
• flower fly
• aphid predator
• biological control
• pollinator
• mimicry
• beneficial insect
• western North America

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• Just Hovering | Bug Squad
• Hello, Friday Fly Day! | Bug Squad
• Bug Squad
• New Website Features Insects of the Greater Yellowstone Ecosystem
• Syrphus-opinator - Entomology Today
• Bug Eric: The Maggot on the Rosebush: Aphid-eating Flower Fly Larvae