The life cycle of Diptera
Although there are a very wide range of species within the order Diptera (over 100,000), they all follow the basic four-stage life cycle: egg, larva, pupa and adult (Cranston & Gullan, 2010). The adult female lays her eggs in a moist environment with lots of nutrients, which makes a corpse the perfect environment. The time taken to hatch from an egg to the larval stage is dependent on the species and the surrounding temperature; the blow fly (family Calliphoridae) can hatch from an egg to the first larval stage in as short as 8 hours (Gennard, 2007)! Once hatched, the larva, or maggot, goes through a number of instar stages, between which the insect molts (Cranston & Gullan, 2010). The larva stage of Diptera may have either a well-defined head, a partially-developed head, or may simply have 'mouth hooks' to indicate the head capsule (Cranston & Gullan, 2010). The maggot then undergoes 'pupation', during which the maggot develops a pupal cuticle, known commonly as a cocoon, to surround itself while it undergoes metamorphosis (Cranston & Gullan, 2010). After an amount of time, the adult fly emerges and is free to reproduce and start the cycle again.
The most useful life stage of Diptera in forensics are the egg and larval stages, as these give the best indication of the time spent on the carrion (Gennard, 2007). However, identification of the immature individuals is difficult, due to the largely similar morphologies between species. Therefore, scientists have developed a variety of methods used to identify the species in question. |
The typical blow fly life cycle. Times given in the chart are for 21 degrees Celsius.
(Image by The Cleveland Natural History Museum, 2011) |