About St Mark's Fly
A small black fly that swarms in May. Males have large heads with huge eyes that almost meet on top.
Did You Know?
Often confused with the larger Bibio marci but emerges slightly later and has entirely dark legs.
How to Identify St Mark's Fly
St Mark's Fly (Bibio johannis) belongs to the order Diptera, family Bibionidae. Adults typically measure 6-10mm.
St Mark's Fly Habitat
St Mark's Fly is found in underground habitats, particularly across Europe. This species has adapted to thrive in its preferred environment, where it can find suitable food sources and shelter.
St Mark's Fly Diet and Feeding
St Mark's Fly feeds on plant roots, typically during its larval stage. Root feeders can affect plant health and are sometimes considered agricultural pests.
Where Is St Mark's Fly Found?
St Mark's Fly can be found in Europe, where it inhabits underground environments. Its distribution is influenced by climate, food availability, and habitat suitability.
Distribution Map
Where St Mark's Fly can be found
Is St Mark's Fly Dangerous?
St Mark's Fly is generally harmless to humans. It does not bite or sting and poses no significant health risk. Like most insects, it prefers to avoid human contact and will typically flee rather than confront a perceived threat.
St Mark's Fly Role in Nature
St Mark's Fly is part of the food web as a primary consumer, feeding on plant material. It serves as an important food source for birds, bats, amphibians, and other insectivores, connecting plant energy to higher trophic levels.
Seasonal Activity
Frequently Asked Questions About St Mark's Fly
What does St Mark's Fly look like?
The St Mark's Fly typically measures 6-10mm.
Where is St Mark's Fly found?
The St Mark's Fly is found in Europe and typically inhabits underground environments.
What does St Mark's Fly eat?
The St Mark's Fly feeds on plant roots.
Is St Mark's Fly dangerous to humans?
The St Mark's Fly is generally harmless to humans. It does not bite or sting and poses no significant health risk.
What is an interesting fact about St Mark's Fly?
Often confused with the larger Bibio marci but emerges slightly later and has entirely dark legs.
Cite This Page
APA:
InsectDiscover. (2026). St Mark's Fly (Bibio johannis). Retrieved from https://insectdiscover.com/insect/st-marks-fly
MLA:
"St Mark's Fly." InsectDiscover, https://insectdiscover.com/insect/st-marks-fly.