Narcissus bulb fly
Merodon equestris
Its grub hollows out daffodil and snowdrop bulbs, which come up blind or not at all. Firm soil into the holes left by dying foliage to deny egg-laying sites.
How to know it
The adult is a convincing bumblebee mimic — a furry brown-and-orange hoverfly, hovering low over the bulb bed on sunny days in late spring. The grub is a fat, dirty-cream maggot, one to a bulb, sitting in a cavity of foul brown mush at the base plate.
What you'll see
- Daffodils that come up blind, with a few thin grassy leaves and no flower.
- Bulbs that fail to appear at all in a clump that flowered well last year.
- A single fat maggot in a hollowed, rotten bulb when it is lifted.
- Bulbs soft and light in the hand, with a hole at the base plate.
- Furry bee-like flies basking and hovering over the bed as the foliage dies down.
Where it comes from
One generation a year. Adults fly in May and June and lay at the neck of the bulb or in the hole left as the dying foliage shrinks back. The grub eats out the center of the bulb through summer and winter, pupates in spring, and emerges as a fly the following May.
Warm sunny gardens with light soil, especially where bulbs are naturalized and never lifted. The open hole left by collapsing foliage is the invitation — bulbs in heavy, settled soil are far less affected.
Dealing with it
- Firm the soil down over the necks as the foliage dies back, closing the holes the flies lay into.
- Lift and destroy soft, light bulbs — one maggot per bulb means every one you remove counts.
- Cover prized clumps with fine mesh during May and June if the problem is chronic.
- Do not replant a bulb that feels soft or hollow at the base.
- Hoe or rake the surface in late spring so no open shafts remain.
Keeping it out
- Plant bulbs deeply, which puts the base plate well out of reach.
- Naturalize in grass or under ground cover rather than in bare, sunny, open soil.
- Buy bulbs from reputable suppliers and reject any that feel light.
- Lift and divide congested clumps periodically, discarding damaged bulbs.
- Grow snowdrops and daffodils in partial shade, which the flies favor far less.
What it goes for
Daffodils and narcissi above all; also snowdrops, bluebells, hippeastrum and other bulbs.
Trouble it brings with it
See also
The Cottage Garden Companion — the gardener's bestiary at cottagegardencompanion.com