Actually it is a hover fly, that you can observe from May to July. Despite its plump shape, that can be likened BUT on the very first superficial view, to a small bumble-bee, it produces a HIGH pitched sound when it is flying.

Here is a link that might be useful: large narcissus bulb fly

Narcissus bulb flies are horrible little creatures, the devour bulbs quickly and by the time you notice the damage it's too late (most of the time).

I use a systemic insecticide every thirty or so days, I'm not sure if this has proved beneficial for anyone but it's worth a shot!

These flies feed on many bulbs in the Amaryllid family such as Daffodils like the name suggests as well as Hippeastrum, Hymenocallis, Nerine, Eucharis and many others!

Thanks for the responses!

I looked up "Hover fly" and the bulk of the literature refers to an insect that is too small to describe what I saw, but the "Narcissus fly" is described in some literature as hovering, so you are probably referring to the same insect.

That looks to be my answer.

Narcissus fly: the size is right (the grubs were large, over a centimeter long and the adults are the size of bumble-bees), the life cycle is right (the literature I saw says they remain in the larval stage over winter and pupate in the spring), the numbers are right (it says the females lay 2-3 eggs per plant before skipping to the next one), the behavior is right (they hollow out the bulbs from the inside), and there are a LOT of daffodils in the garden to attract pregnant females and expose the hippeastrums.

Well, dangit. It's easy enough to protect amaryllis from narcissus flies if I ever put them out again: I can use some more neem oil or make closer inspections. But now I'm worried that we won't see many narcissus next spring. This year a lot of rain allowed the daffodils to retain their green leaves through July, so I was looking forward to a big show next year where they maintained their size and multiplied. But this summer when I was digging through the garden planting perennials, I came across a few daffodil bulbs that looked dead/rotted, and hoped it was just an anomaly and those individuals had gotten waterlogged for some reason during the rain. I hope the whole crop hasn't been destroyed by the flies.

Thank you both for your answers. I didn't think I'd get an explanation so quickly!

Does your feedback indicate that you bothered yourself, to search for hover flies in general, rather than directly clicking on the link that I concluded my message with?

I have had problems with this bugger over the years, but mostly in my non-Hippeastrum, although they too have been attacked! I use the Bayer product with Imidacloprid as a soil drench and it seems to solve the problem. Or at least I have convinced myself that it does so I keep buying it. Best of luck getting rid of them :o) Dan

@haweha

Sorry I didn't notice your link! Since the alignment of the line was different I just thought it was part of the site and not something you wrote. I see it now, and those articles are helpful.

Thank you for your feedback.
Additional info.
The BIG Narcissus fly is the main "predator" and it will "infect" healthy bulbs in the GREENHOUSE even. In this case, due to the elevated temperatures THERE, the "Imagos" (the Adults) will hatch and breed sometwhat earlier than outside. They will start reproductive activity in spring when temperatures exceed 18 degree Celsius. In the Greenhouse, curing should start from APRIL on.

For many years I was wondering why my daffodils were not multiplying, and even disappearing. Then, the same year I acquired Compulsive Hippeastrum Acqusitiveness Disorder (obssesion) - also know as CHAD - I learnt of the NBF, and lost a few bulbs in later years. Now, I don't take my plants outside until July - well past daff season - in the hopes the fly will have disappeared by then - I think someone here recommended that. This year by bulbs are enormous - and I cringe to think of the possibility of something being inside these healthy looking bulbs.