BLOWFLY

Key features

Adult flies are generally 9 – 13mm long with a wingspan of 18 – 20mm. The adults are large robust flies. with a stout abdomen. The thorax is black/blue and dusky, and the abdomen is likewise coloured.

Biology

Blowflies are primarily scavengers, depositing their eggs on fish, meat, decaying matter of animal origin and wounds of animals and man. In the absence of more favourable sites, they will lay their eggs on animal faeces and decaying vegetable matter. The females usually lay around 600 eggs – each egg being 1.0 – 1.5 mm long and creamy white in colour. The eggs hatch within 18-48 hours. The egg period varies according to the age of the egg when laid, and on temperature and humidity. However, when gravid females cannot find suitable laying sites, they retain eggs for as long as possible. In such circumstances, eggs hatch in a very short time, in fact, Calliphora spp have been seen to deposit living newly hatched larvae rather than eggs. Caliiphora spp usually oviposit at night. At temperatures below 41, eggs will not hatch.
From the eggs the larvae emerge and feed on the rotting meat, etc. Larvae grow rapidly and moult three times. Within 14 days, they have developed fully. Before pupation, larvae cease feeding and tend to migrate from the feeding medium. By choice, pupation takes place in loose soil. if this is not available. then cracks in walls, under sacks, etc will suffice. The length of time spent in each larval stage is variable – again being dependent on temperature, humidity and foodstuff.

Tolerance of low temperatures by eggs, larvae and pupae is exhibited and in such conditions, development periods are greatly extended. The following figures (for Calliphora vicina) are therefore only a guide.

Speed of development

(27°C on liver – time in hours):

  • Egg
  • 20 – 28
  • 1st stage larva
  • 18 – 34
  • 2nd stage larva
  • 16 – 28
  • 3rd stage larva
  • 30 – 68
  • Prepupa
  • 72 – 290
  • Pupa
  • 9 – 15 days

Distribution

Worldwide – always closely associated with man and his dwellings. Significance
Blowflies are attracted to rotting animal remains on which to lay eggs. in their search they can mistake stored meat as a suitable “host”. The possibility of disease spread is similar to the housefly.

Control

Treatment consists of finding the source of the infestation and, where possible, removing it.
The application of a residual insecticide may also be indicated, however attention to hygiene is the key to controlling this pest.

Illustration: Calliphora vomitoria adult.

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