Small-headed Fly
Gallery Location
Not on View
Geography: Place Collected
North America, Canada, Ontario, Nipissing District
Object number
ROME203683
Taxonomy
- Kingdom Animalia
- Phylum Arthropoda
- Class Insecta
- Order Diptera
- Family Acroceridae
Department
Natural History: Insects & Arachnids
Description
The thought of harbouring a parasite within yourself is truly terrifying. Spiders live with this constant threat.
The small-headed fly (Diptera: Acroceridae) is a proficient parasitoid that specializes on spiders that are found worldwide. As their name suggests, these flies possess comically small heads, compared to their more robust bodies. Their yellow and black markings help them avoid predation as they resemble bees and wasps; insects that most predators avoid. Some species even possess extremely long mouthparts that aid them in collecting nectar from flowering plants.
However, their deceiving adult forms are the result of a gruesome early life stage: their larvae spend most of their lives living inside the abdomen of living spiders. First-instar larvae, also known as planidia, seek out spiders and burrow into them, where they remain until they are ready to metamorphose into adult flies. The entire process can span multiple years if the larvae enter diapause (a period of suspended development in insects). Pupation takes place outside of the spiders and the way the larvae burst out spells certain doom for their spider hosts. These infections may not always be successful, as it is found that some spiders can suppress the infection when parasitized by only one fly larva.
One can certainly expect an extensive evolutionary arms race between these flies and spiders.
If you see an error or have additional information, please contact us.