Narcissus Bulb Fly (Merodon equestris) — identification, habitat & look-alikes

The narcissus bulb fly is a hairy that looks much like a small bumble bee. Its maggots tunnel into and hollow out daffodil and other bulbs, and the fly reached North America from Europe in shipments of infested bulbs. It's also called the greater or large bulb fly.

Appearance

Appearance: A stout, hairy fly about 1/2–5/8 in (12–16 mm) long, patterned in black, orange, and yellow. Color patterns vary a lot from fly to fly.

Look-alikes

Bumble beesBombus

This fly has just one pair of wings and very short antennae. Its hind thighs are thick, with a triangular bump near the tip.

Why they get mixed upIt's a bumble bee mimic, hairy and banded in similar colors.

Lesser bulb fliesEumerus

Lesser bulb flies are noticeably smaller. Their larvae usually move into bulbs that are already rotting.

Why they get mixed upTheir maggots also turn up inside bulbs, including onions and other alliums.

Where it lives

Typical habitats: Gardens
Parks
Bulb farms
Range: Native to Europe. In North America it occurs from British Columbia south to California and has turned up elsewhere, including Colorado, wherever infested bulbs were planted.
Preferred conditions: Strongly tied to people: suburban gardens, parks, and bulb fields. In Colorado it shows up patchily, spreading slowly from spots where infested bulbs were introduced.
When to see it: In Colorado
Active Apr–Jun

Behavior

Diet: Adults sip nectar and eat pollen from many kinds of flowers. Larvae feed inside bulbs.
Activity: In Colorado, adults are out from late April or early May through June. They fly low and fast in zigzags and often rest on leaves or bare ground. Each adult lives about 2½ weeks.
Overwintering: Full-grown larvae spend the winter inside the bulb, then crawl out in early spring to pupate about an inch below the soil surface. There's one generation a year.

Life cycle

Larva: A plump, dirty-white maggot up to about 3/4 in (19 mm) long with no distinct head. It enters at the bulb's and eats out the center; rot often follows. Lightly infested bulbs send up only a few thin, grassy leaves and don't bloom, while badly infested bulbs turn soft and brown.
Caterpillar food plants: Daffodils and other narcissus are hit hardest, but hyacinths, some lilies, amaryllis, tulips, irises, snowflakes (Leucojum), and squills (Scilla) are also attacked.

Conservation

IUCN Red List: LCLeast ConcernLow risk of extinction

Culture and stories

Culture and stories: In Pacific Northwest gardens, the usual advice is to throw out soft bulbs, plant bulbs deep (about 10 in), and cover the foliage with row cover after bloom so females can't lay eggs.