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A commonly found parasite of the Far North, especially in rainforest areas, is not a worm but a maggot (larvae) which occupies the frog on a temporary basis. With the parasitic fly Batrachomyia sp., the adult fly lands on the frog and lays its eggs under the frog's skin. The larvae then develop and, when they are ready to pupate into a fly, they use three hooks on their 'head end' to cut their way out from under the frog's skin before dropping into the soil to pupate. The photo at left shows one of these larvae under the skin of a White-lipped tree frog (Litoria infrafrenata). The colour of the frog itself shows that the animal is stressed. Once the larvae was removed, the frog immediately returned to normal green colouration and resumed its normal behavior and eating.

These larvae are usually noticed under the frog's skin during southern hemisphere winter but the eggs themselves are laid during the summer wet season. They grow during the winter dry season and cut their way out of the frog at the beginning of the next summer. The one pupa that we successfully hatched out so far took between one to two months before a plain looking fly - like a house fly - hatched out but with shorter, straight cropped wings.

One or two larvae per frog is common but we have received reports from the Tully area (about two hours drive south of Cairns) of frogs with more than five larvae under the skin. During the 2000 winter season (just as the drought was getting started), as many as twelve per frog were reported! One larvae is enough to cause stress and irritation to the frog which makes it stop feeding and lose condition. More than three larvae can constitute enough of a burden on the frog to kill it.

We noticed that reports of Batrachomyia larvae in frogs stopped entirely during the severe drought (2001 to 2003) but resumed again after the drought was officially broken. The worst reports of multiple larvae were following very heavier wet seasons. This implies that the Bot fly in this area would almost certainly be impacted by increased El Nino events and climate change.

There has been some study of the Batrachomyia fly but many questions remain. There appear to be more than one species. The photo at right above shows a larvae of one of the smaller species which has been found in frogs to the north of Cairns (the actual size was 4mm long).

Why the fly lays its eggs under a frog's skin is a mystery as well. Is it just a safe hiding place for the larvae to develop? Is there some kind of enzyme or nutrient that the larvae obtains from the frog that isn't present in other animals? There is a tiny hole in the frog's skin at the posterior end of the maggot's body - is this for the ejection of wastes? What exactly is the larvae feeding off while it grows in the frog?

If you live in Far North Queensland and encounter one of these frogs, phone us to discuss what to do with it. With some instruction, the larvae are not too difficult to remove but wait until you have received guidance before attempting to remove any larvae yourself. If the pattern of larvae numbers is indeed tied to the amount of rain in the summer, we expect reports of multiple larvae burdens this winter (2006) as we have just had the first "normal" wet season we've had in many years.

We are also interested to receive frogs with these larvae from north of Cairns so that the different species can be pupated, hatched and sent to entomolgists for species identification.

last edited: May 14th, 2006