Rat Tailed Maggot: Statement by Dr Ivan Toms, Director: City Health

Following media coverage around the issue of the "rat-tailed maggot" there have been at least seven new complaints of finding the maggot at homes in different parts of the city e.g. Elsies River, Sybrand Park, Goodwood, Ottery and Grassy Park.

A group of experts have reviewed all the evidence so far and there is nothing to suggest that these maggots are present in the municipal water supply. The main reason that we believe this is not the source of the problem is that the water is chlorinated and filtered and comes from dams in the mountains where it is extremely unlikely that this maggot would be found, as it does require a nutrient rich environment to grow and develop. Should a maggot be present in the untreated dam water, it cannot pass through the City's robust water treatment filtration process.

City Water Services' Scientific Services Section also has an intensive Microbiological Programme which tests the bacterial quality of water in the drinking water supply on a weekly basis. Our drinking water is of consistently high standard, and occasional poor results are immediately investigated further so that the problem can be rectified.

Therefore, as Director: City Health, I would like to reassure the public that in my and the experts' opinion the City of Cape Town's water supply to your home is clean and safe to drink.

The question therefore is where do the maggots come from, if not from the water supply? The working theory that seems to fit the life cycle of this fly is that the drone fly, which feeds on nectar from flowers, lays its eggs in some area of reasonably stagnant (or at least not fast flowing) shallow water that has a suitable food source (e.g. decomposing leaf material or other organic matter). Most cases where the maggot has reported to have been found (and in almost all cases it is one or two maggots) have been in the hand basin or toilet bowl, near an outside tap or in the open channel below a row of hand basins. They may also be found naturally in still, stagnant areas of rivers or wetlands, drainage ditches and even garden ponds.

An example of a possible place that the egg may be laid inside a building is in the p-trap on the outlet of a hand basin. The egg then hatches as a small 1mm maggot which then grows to the size of the maggots (technically larvae) that have been seen of about 2.5cm long with a "tail" which is actually a breathing tube. When the larvae is mature it wriggles out of the water to a dry area nearby (such as the side of the hand basin) to pupate (the next phase of its life cycle) before becoming an adult drone fly.

In cases where people have found a rat-tailed maggot in their toilet bowl it is possible that the maggot originated in the septic tank (if a septic tank exists) and then travelled back up the pipe into the toilet. The eggs could also have originally been laid in the cistern or under the internal lip of the toilet bowl. Alternatively, the maggot may have come from a poorly maintained holding tank in the building. If this occurs, building maintenance staff should check tanks for openings which could allow the adult fly in. These tanks should be cleaned regularly to prevent the possibility of small organisms passing through water pipes in the building.

If residents come across the maggot they should contact City Health's Mr Richard Kotze on 021 980 1303. We will send out an environmental health practitioner (health inspector) as well as a water inspector to visit your home, take samples and look for possible local breeding places.

All the complaints are being coordinated and then reviewed by experts from both City Health and Water Services with the assistance of a university entomologist.

It is not clear if the reason we are finding a fair number of these maggots in different parts of the city is due to increased public awareness through the media reports or because there has been an increase of drone flies in Cape Town.

A number of the media reports have contained highly exaggerated and in most cases untrue suggestions of the possible health implications of drinking a maggot. Since the rat tailed maggot is quite large and clearly visible to the naked eye, it is highly unlikely that it would be ingested in the first place! There have been absolutely no reports of anybody in Cape Town getting sick from the rat-tailed maggot and an internet search reveals a case in South Australia where the person passed the maggots in the stool (1 to 3 larvae on about five occasions over a two week period), whereupon they spontaneously ceased to occur. That was the sum total of the resultant health implication in this case.

It is extremely doubtful that the larvae could survive in the environment of the gastrointestinal tract, particularly in the high acid content of the stomach, if ingested. Media speculation that the fly could lay its eggs around the anus and the larvae penetrate further into the rectum is a theoretical possibility - but again no such case has been seen in Cape Town.

The City is committed to ensuring good public health for all residents of Cape Town and there is no reason at all to believe that public health is at risk in this case. We would encourage the media to be responsible in reporting this issue and to assist us to communicate the realistic facts rather than highly suspect and sensationalistic reporting that has occurred in some instances.

Issued By:

Charles Cooper
Media Liaison
Tel: 021 400 3719
Directorate: Communication and Marketing
City of Cape Town
Email: media@capetown.gov.za
Tel: 021 400 2201
Fax: 021 957 0023

Media Queries:
Dr Ivan Toms
Director: City Health
Cell: 084 220 0143