T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network


Fly (Hover) Narcissus bulb fly (Merodon equestris)

Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Diptera
Family: Syrphidae
Genus: Merodon
Species: M. equestris
Binomial name: Merodon equestris
Synonyms: Eristalis narcissi, Merodon narcissi, Merodon transversalis,
Merodon validus, Syrphus equestris.
Common name: Narcissus bulb fly, Bulb fly, Greater bulb fly, Large bulb fly, Large Narcissus fly, Narcissus hoverfly.

Merodon equestris is a European species of hoverfly native mainly the British Isles. In 1906 narcissus bulbs imported from Britain were found to be invested with this fly. Originally it was found in Invercargill but it has been found in imported bulbs at Auckland. The fly is now spread through out the country.
Like other hoverflies it displays a colouration pattern that mimics a stinging insect (a bumblebee in this case) as an evolutionary defense mechanism. This hoverfly which has taken on the characteristics of the bumblebee including its colouration and hairy carapace. This can be misleading to birds and other animals who may try to eat it or interfere with its feeding.

M. equestris is on average 12 millimetres in length and is orange, black and yellow in colour. The legs of this species are always black. Patterns of venation on the wings can be used to identify the species.
Males and females display a body dimorphism common among hoverflies. The eyes of the male are larger and almost touch along the top of the head, whereas females have smaller eyes which are placed farther apart. Females also have a pointed abdomen with inconspicuous genitalia while males have curved asymmetrical genitals.

M. equestris is a flower fly that feeds on the pollen and nectar of flowers from the genera Lilium and Narcissus.
The larvae of these flies are known pests found on the bulbs of Narcissus, Hyacinthus and other spring flowering bulbs, particularly those growing in open, sunny situations. This has lead to the names “Bulb fly” and “Narcissus fly”. This is unlike most other members of the family Syrphidae, which predate on aphids.
The affected bulbs contain a single, cream/brown larva, which is up to 20mm long, usually surrounded by a brown excrement. If foliage is produced it is narrow, yellow and distorted and the plant does not usually flower.
The flies, which emerge in late spring/summer, are about 15mm long and are similar to small bumblebees, also making a humming noise when in flight.
The female usually gets to the neck of the bulb through the hole left by the foliage in the summer. She lays up to 100 eggs near the neck of the bulb which hatch about a week later. The legless larvae crawl to the base of the bulb and tunnel into the interior to start feeding on the central part of the bulb, which includes the following year’s flower buds. Generally there is only one larva per bulb and it feeds for around 6 months until spring when it leaves the bulb to pupate in the soil.

The next two photos below are of a female Merodon equestris. It is easily identified as a female because her eyes are apart. These photos shows why people think this chubby hairy fly is a bumble bee.




Photos below are of a male Merodon equestris