Behaviour

Little is known about the behaviour of adult flies because they are so rarely observed in the wild. Observations have been carried out using binoculars which indicated that on hot and sunny days, females move around the neck and head regions of rhinoceroses, attaching eggs to the skin mainly near the horns. However, eggs are also found elsewhere, including:

  • at the base of the ears
  • on the neck and shoulders

Disease

While adults of Gyrostigma rhinocerontis are harmless, if alarming because of their size and clattering flight, their larvae are obligate parasites of both the black rhinoceros (Diceros bicornis) and white rhinoceros (Ceratotherium simus).

Females deposit their eggs around the head and neck of the rhinoceros and attachment organs on the eggs help them to stay in place on the skin. No-one knows how the hatching larvae enter the digestive tract, but they might be ingested during grooming or mutual grooming or disperse across the skin surface to the mouth as in some of the horse stomach bot flies (Gasterophilus species).

The second and third stage larvae feed and mature in the host’s stomach, firmly attached to the mucosa with the aid of their robust mouth hooks. These hooks possess somewhat overlapping barbs, like roof tiles, which may act like the barbs of an arrow to help the larvae retain their hold in the mucosa.

Early publications based on studies of dead rhinoceros reported that "most of the stomach (was) practically studded" by larvae and that several hundred larvae could be present producing "quite impressive" pits in the stomach wall.  

Although the feeding activity of the larvae does result in lesions on the mucosa, severe pathological effects have not been reported, indeed rhinoceroses seem to tolerate a great number of larvae without showing any signs of illness. It has also been noted that, when larvae are removed from the stomach wall and placed on the human hand, the large mouth hooks could "produce a sharp pain"!

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