Friday 9 January 2015

When is a Bee NOT a Bee?

Narcissus fly. Photographed by Ed Phillips
A few years back, I spotted something that looked like a bumblebee and flew like a bumblebee foraging on the flowers just outside my kitchen window. There was something unusual about it that I couldn't quite put my finger on, so I took a quick snap shot and uploaded it to my laptop for a closer look.

Lo and behold, it wasn't a bumblebee at all! Although it had been difficult to tell from a distance, I could see straight away from the image on my laptop that this insect had large prominent 'fly' eyes that almost joined together in the middle of her head and that her antennae were short and stumpy; entirely unlike a bumblebee who would have ovoid eyes on the side of her head and whose antennae would be long and beautifully elegant. On further examination I noticed she was missing the 'waspish' waist that characterises all bee species and I could also see that she only had one set of wings rather than two.

I was most surprised. For all the world this creature had looked and acted like a bumblebee, but clearly she wasn't. She turned out to be Merodon equestris (Narcissus fly) one of our 250 or so UK hoverflies. A fly pretending to be a bee…..

Batesian Mimicry

I already knew about 'Batesian mimicry' which is where a harmless species has evolved to mimic the warning signals given out by a harmful species. One of the most obvious examples of this form of mimicry is where hoverflies imitate wasp coloration in an attempt to avoid predation by birds and other predators. My understanding previously however, had been that whilst bees 'flew'- hoverflies 'hovered'.  Not so this hoverfly! Merodon equestris has taken Batesian mimicry to its extremes. Not only does it look like a bumblebee with its long hair and chunky striped markings, but it has actually evolved in such a way that is able to fly like a bumblebee too…..although a little more rapidly and it can still hover. Incredible.

For a while I revelled in the fact that I had discovered this clever little bumblebee look-alike in my garden. Until I began to read more….

Narcissus Fly

Once I'd got over the excitement of there being a hoverfly that looked so much like a bumblebee that she had completely pulled the wool over my eyes, I began to wonder why this particular species of overfly has been endowed with the common and rather ominous sounding name 'Narcissus fly', or 'Bulb fly'.

After further research it soon became evident that the larvae of the Narcissus fly (Merodon equestris) wreak havoc on your narcissus and snowdrop bulbs, not to mention your daffs, your tulips, your hyacinths, your lilies...

It seems the adult female lays a single egg between the layers of skin enclosing the neck of each bulb, but as she is capable of laying up to 100 eggs in her lifetime she has the potential to devastate your flowering bulbs. Once the eggs hatch, the larvae bore inside the base of the bulbs and then tunnel up to feed of the fleshy leaves near the growing points of the plants. A large cavity is produced inside the bulb from which the larvae then move into the soil where they pupate. Five to seven weeks later the new adults emerge and the life cycle starts all over again.

Oh dear, this was not good news. I love my snowdrops!

Controlling Narcissis flies

What can we do then, without resorting to pesticides, to prevent these furry little hoverflies, which are on the wing from around early May till late June, from wreaking havoc upon our bulbs?

There is a lot of information out there when you start to search, but as I choose to garden organically I am only interested in the chemical-free options. Unfortunately this little insect has few natural predators and doesn't seem to be deterred by non toxic household concoctions, so preventing the fly from laying her eggs in the first place and/or disposing of her larvae are the best ways to protect your plants. All methods of control are, I'm afraid, fairly labour intensive but it's worth trying the following….

1. Mow the leaves as soon as they dry in late spring and then press the soil down firmly to prevent newly mated female flies from finding the holes.

2. Cover the bulbs with fine mesh to prevent the adult fly from laying her eggs.

3. Catch the adult flies in a net and remove them from your garden.

4. Infested bulbs can be submerged in water, kept at around 44 degrees, for 40 minutes…..but take great care not to overheat as this could destroy the bulb too.

Good luck!

Having read a lot about the Narcissis fly and ways to prevent her from destroying your bulbs, I thought I'd share my favourite article  with you. It's written by Val Bourne who has been a committed organic gardener all her life. So, no nasty chemicals in her garden, even when she goes into battle with Merodon equestris.

To discover more about our wonderful and diverse UK hoverfly species, please check out this site. It contains loads of interesting information and lots of great photos and illustrations to help you identify the hoverflies visiting your garden…..

All About Hoverflies

If you are interested in learning more about insects in general….or in helping prevent their decline  … please consider joining BUGLIFE  . For as little as £2 per month you can help this charity make a real difference.

Many thanks to Ed Phillips for allowing me to use his beautiful photograph of Meredon equestris. You can find more of his wonderful photographs here - Ed Phillips Wildlife

Thank you for reading this post x

Episyrphus balteatus (marmalade hoverfly

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