Nasal Bot Flies of Sheep

These are larvae or maggot of Oestrus ovis also called nasal bot fly which are mostly present in sheep and goat. Their effect sometime not significant and owner don’t understand about it.

Nasal Bot Flies of Sheep

The Bot flies usually attacks cats, dogs and human. In these hosts it present in eye and throat and cause irritation there, cause difficulty in breathing when in nasal tract. Bot flie develops and mature in sheep and goat but not in other above mentioned species.

Nasal bot fly

Nasal bot fly was exposed in Australia in sheep and goat in 1900s and firstly discovered from Western Australia in 1919. By the using of anthelmintic drugs such as ivermectin, it has been controlled in many areas.

It caused infestation to host animals but owner does not know about infestation without seeing expelled bots from animal. Flocks of animal show disturbance and different symptoms such as nasal irritation and shortage of breathing individually due to attack of bot fly.

Life cycle

Flies mostly attack in late summer and in spring when temperature is higher than 20℃ and it varies according to regions. Life span of bot fly varies in different temperature such as two days in hot climate and four weeks in cold areas. In Russia or Siberia, they have two generation as well as five or six generation in Australia in year.

Larvae of bot flies are infective form in sheep as horse bot fly (Gasterophilus sp.) lay eggs on horse hair. After deposition of larvae in nostrils of sheep, it starts to move and grow in frontal sinuses and nasal cavity.

They develop and mature into third stage of larva which is 3cm in length. This is diagnostic stage because it moves out when sheep sneezed. Development rate of larvae in head of sheep is variable, long as 10 months and little as six weeks. Life cycle is variable and dependent on temperature.

Effect of nasal bots

Sheep shows disturbance in its behavior otherwise infestation is mostly unnoticed. Sheep are gathered where flies are less active in shaded places. Infected sheep show signs of symptoms such as difficult breathing, nasal discharge, coughing and sneezing.

It causes economic loss such as reduction in fleece growth. It also suppressed immunity and open gate for bacterial infection. Nasal bot fly also attacks on dog, cat and human. It causes severe irritation in eye and throat in these species. It does not mature other than sheep and goats only cause infection in that species.


There is no diagnostic technique or test to identify it. It may detect through particular behavior of animal.  Animal is seemed like susceptible with or without nasal discomfort but it is not able to diagnosis for this disease. Bots may be diagnosed by chance, during removing of hairs or moving out from the nostrils from the sheep.

It may be found on feed trough or water. Bots mostly attack on horned sheep and it enters in sheep from horned core when these are dehorned. Bots do not show any sign of infestation, it can be diagnosed by its behavior.


Effective product can be used for its treatment with indirect diagnostic method.  If this treatment is effective against it then signs of infestation may be disappear.  Different anthelmintic drug are used for nasal bot infestation in sheep.

Three registered macrocyclic lactone such as abamectin, ivermectin, closantel and moxidectin are effective against this disease in caprine. Abamectin is registered for goat specifically.

Authors: Muhammad ShafiHasni, Muhammad Kasib Khan, SyedaRoshan-e-Tahir, Muhammad Nadeem

  1. Department of Parasitology, University of Agriculture Faisalabad-Pakistan

*Corresponding author email:

By Shafi hasni

PhD Scholar