Behold, the narcissus fly larvae. This creamy brown grub is not your garden friend. In fact, in the world of insects, grubs and greeblies that would have been better kept out of this country, the narcissus fly ranks up the scale. It is European in origin – what they call a hoverfly though not a desirable species.
I had to look it up because I only knew it as the narcissus fly. It is Merodon equestris, in case you want to know. On the wing, the adult looks inoffensive – a bit like a cross between a lean, mean bumblebee and a blow fly boasting a yellow back. It is its reproductive habits which are the problem. The female adult zips around at great speed, laying its eggs, usually one by one, at the base of the bulb foliage. When the egg hatches, the juvenile larva burrows down and makes a cosy home for itself inside the bulb where it sustains itself by eating it from the inside out, in preparation for hatching the following spring.
You can see the damage in the photograph. As I was redoing the rose garden, I was splitting clumps of bulbs in full growth (not generally recommended but I find it works out fine as long as I am replanting straight away into good conditions). Some of the bulbs were soft and sporting very few, if any, fresh roots. That is a sure sign of narcissus fly. There is something deeply compelling about squeezing the bulb and having the larva exude out the top, or splitting the bulb and digging it out. They are quite tough so difficult to squish between your fingers (I wear gardening gloves at all times, lest you recoil at the thought) but can emit a satisfying pop and explode in a very small way if you squish them below foot. Generally, there is only one per bulb.
While this critter is widely referred to as the narcissus fly, by no means does it limit its predations to daffodils. It attacks many members of the amaryllidaceae family. This is a fairly large family and includes snowdrops (galanthus), snowflakes (leucojum) and hippeastrums. According to bulb expert, Terry Hatch, it also attacks hyacinths but as we only have two hyacinths, we have never noticed. As an aside, hyacinths need a winter chill to flower well so are better in colder climates.
You can’t eradicate it. The fly is airborne and does not respect boundaries. A multi pronged defensive strategy is required. The fly does not like shade, so all our hippeastrums are now woodland plants because they were getting hammered by the larvae infestations. Now they are untouched.
We favour the early flowering narcissi because they are done, dusted and pretty much dormant by the time the fly is on the wing in late spring and summer. The galanthus are also back below ground by then, so it is never a major problem with them. It doesn’t seem to be a problem with the autumn flowering bulbs such as the nerines and the belladonnas, even though, sitting half in and half out of the ground, you would think they might be vulnerable.
Don’t let your daffodil bulbs become so congested they squeeze themselves above the ground and planting them in shallow bowls may be like a creche to a passing fly. Most of the advice is to leave the foliage on the bulb until it turns yellow and dies off naturally because this is how the bulb builds up strength to flower again next season. You are not meant to tie it in knots or plait it (as some tidy gardeners do) because that inhibits the photosynthesis process. However, a visiting daffodil breeder told us that in fact the bulbs only need 65 days to fortify themselves which is a great deal less than nature gives them. The daffies in our lawn are somewhere over 100 days. This is not universally acclaimed advice but if you have a problem with bulb fly, removing the foliage soon after two months and piling extra dirt or mulch on top of the bulbs may help to break the cycle. The worst that will happen is that your bulbs won’t flower well if you strip off the leaves too early.
Come spring, Mark can be found stalking narcissus fly in our rockery. They become active in the warmth of the day. They are very quick so it is hard to get them with a fly swat. He uses a little sprayer of Decis and squirts them. Decis is a synthetic pyrethroid (as is fly spray) so not a particularly nasty insecticide. Vigilance is what keeps the flies under some semblance of control here. Though he was a little wry on the day he told me he had been walking through the rockery minus his sprayer when he saw an offending fly. It was an open garden day so he looked around to check that no visitors were within view, took off his tee shirt and was stalking the offender to swat it when he noticed the woman at the side of the garden watching. “Eye candy,” I told him. “You are now officially eye candy.”
Left to right: a perfectly healthy bulb, an infested bulb which had already formed a healthy offset, the offending larva in front, and a second infested bulb with it’s larva still ensconced (but no longer – I squished it after its photo shoot).
First published in the Waikato Times and reprinted here with their permission.