When is a bee not a bee?

20 January, 2008

Rat-tailed Maggot Fly, Eristalis tenax
A bee mimic: a Rat-tailed Maggot Fly (Eristalis tenax)
Image: Arturs Neboiss
Source: Museum Victoria

Question: My husband and I were having lunch in the garden this week and our attention was drawn to the large number of bees feeding on the flowers around us. There seemed to be two different types of bees in the garden. They all looked like introduced honeybees, but some were bigger and had larger eyes than the others. We thought the larger ones were male honeybees (drones), but perhaps they're different species of bee. Can you help?

Answer: The bee on the left is indeed an introduced European Honeybee (Apis melifera). It is a worker bee and therefore a female.

You are right in saying that male honeybees, or drones, are larger than the female workers and have larger eyes, but drones do not collect food for themselves or the hive. They are fed by the workers - their sole function in life is to mate with new queens. Therefore, the larger "bees" you saw feeding on the flowers could not have been male honeybees. In fact, they were not even bees.

The insect on the right is actually a fly, commonly known as the Rat-tailed Maggot or Drone Fly (Eristalis tenax). It looks and behaves like a bee, but if you look carefully you will see that its second pair of wings is reduced to small club-like structures known as halteres. These structures are possessed by many of the fly species and are used to assist with flying. 

Rat-tailed Maggot Flies are excellent mimics of European Honeybees. This is a very clever strategy for an animal with few defences: if you look like an animal that has a painful sting, predators are much more likely to leave you alone.

Adult Rat-tailed Maggot Flies feed on nectar. They are important pollinators and are particularly attracted to yellow flowers. The larvae can be up to 20 mm long and feed on decaying organic matter or highly nitrogenous waste found in places such as drains, sewers and slurry from dairies and kennels. The larvae have a long breathing tube 30 to 40 mm long on their rear end, which gives them the appearance of being rat-tailed. The tube acts like a snorkel and they use it to breathe when they are submerged in their feeding material.

The Discovery Centre has identified a number of these Rat-tailed Maggot larvae for people who have found them in their toilet bowls. Larvae feeding in the waste in septic systems can get drawn into the system when the toilet is flushed. This has caused people to panic, assuming that the maggot has come from them. However Rat-tailed Maggots are not an internal parasite of people.  

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