Life of the Miscellaneous True Fly: the false-legged flies 

Miscellaneous true flies are fascinating benthic macroinvertebrates that go through a complete metamorphosis, involving the four stages of the life cycle; egg, larval, pupal, and adult stage. Today, we will explore: What happens after the miscellaneous true fly pupae leaves the safety and familiarity of the water? And how does the miscellaneous true fly pupa transform into its adult form? To explore these questions, we’ll start at the very beginning-- when the miscellaneous true fly eggs are first laid.

The eggs of miscellaneous true flies may either be deposited on the surface of a water body or on submerged substrate or vegetation. They will hatch within a few days to several weeks depending on the species, after being laid.

The larval stage has approximately 3-4 stages of development, known as instars. The first instar development takes the shortest time followed by longer amounts of time spent in each subsequent instar development as the larval will require greater amounts of energy. This energy is required in order to be ready to enter the pupal phase.

The pupal phase typically lasts two weeks and involves four different possible pupae. The pupa may anchor their cocoon to stream substrate and once the adult emerges it has to swim up the water surface. In other cases, the pupa cocoon may float to the water surface once its ready to emerge as an adult. Yet still in other cases, the pupa may crawl onto the shoreline and dig into the substrate during its larval phase in order to develop as a pupa in these conditions. Lastly, a pupa may be ready to develop into an adult once it has entered its fourth and last instar development as this last exoskeleton will serve as the pupal case.

Depending on the species, the adult life cycles of miscellaneous true flies look very different. In general, the male dies after mating, while the female goes off in search of a blood meal to ensure her eggs get the nutrition they require. After laying her eggs, which can vary from one batch to several, the female also dies.

It is important to note that there are several other benthic invertebrates that are referred to as ‘flies’, including mayflies, dragonflies, stoneflies, caddisflies, alderflies and fish flies. These flies do not belong to the group diptera. The flies in this group are differentiated from these other groups because they only have one pair of wings and they do not have any legs. They move around by using different appendages, including creeping welts, prolegs, or suctorial discs.

Fun Fact:  The scientific name diptera comes from the word ‘di’ meaning two and ‘ptera’ meaning wing. This is because as adults, true flies have only two wings unlike other flies.

Fun Fact: In colder climates, it can take up to 2-3 years for a true fly larva to develop into an adult.

Fun Fact: True flies are both beneficial and a nuisance for humans. They are important in the pollination of flowers, and serve as prey for other animals such as bats, however they can also spread diseases that can affect humans such as malaria and yellow fever.

Interested in learning more about benthic macroinvertebrates and how they can be used to measure the health of rivers and streams? Be sure to follow EcoSpark’s social media to stay updated on our Changing Currents program and our other citizen science and environmental education programs.

References

• Do my Own Pest Control. (2018). Fly Inspection Guide. Retrieved from: https://www.domyown.com/fly-inspection-guide-a-508.html

Carina is the Environmental Education Lead Instructor at EcoSpark. She holds a Bachelor of Honors in Environmental Studies and a diploma in Ecosystem Technology, both of which developed her interest in using geographic information systems to communicate about complex issues, such as climate change. In her role as Lead Environmental Educator, Carina designs geospatial education tools for EcoSpark’s citizen science programs. When outdoors in the field, you will often find her streamside identifying aquatic critters, communicating her enthusiasm for the outdoors, and demonstrating her dedication to stewardship practices with youth and adults throughout the GTA.