The Phorid fly family contains a diverse group of insects, but the common name, “coffin fly,” refers to a particularly unusual aspect of their biology. These insects possess a specialized survival trait that allows them to access protected food sources. Their unique ability to bypass barriers that stop nearly all other flies gives them a surprising role in fields ranging from public health to criminal investigation.
Defining the Coffin Fly
Coffin flies belong to the family Phoridae, a large group often referred to as “humpbacked flies” due to the pronounced arch of their thorax. They are small insects, typically measuring between 0.5 and 5.5 millimeters in length, and are sometimes called “scuttle flies” because they run erratically across surfaces rather than flying. While the classification includes several species, the one most commonly associated with the name “coffin fly” is Conicera tibialis. Phorid flies thrive in decomposing organic matter, including fungi, plant material, and animal remains, but they are also found in places like ant nests and sewer pipes.
The Ability to Penetrate Deep Barriers
The most remarkable trait of the coffin fly is the adult female’s capacity to actively burrow through significant physical barriers to lay her eggs. Female coffin flies, specifically Conicera tibialis, can dig down through more than two meters (over six feet) of soil to reach buried remains. This feat is accomplished by the adult female fly itself, which uses specialized physical and behavioral adaptations to navigate the dense earth.
The female fly is hypothesized to employ a combination of strong legs and a hardened body structure to push through the compacted soil. This digging allows her to access the protected, stable food source of a buried corpse, which remains viable for decomposition long after surface remains have been consumed. Once the female reaches the target, she lays her eggs directly on or near the remains, and the resulting maggots feed on the tissue. This process allows entire generations of coffin flies to complete their life cycle underground.
Why This Ability Matters
This deep penetration ability is of considerable importance in the field of forensic entomology, the study of insects in criminal investigations. The presence of coffin flies on human remains provides a distinct indicator for estimating the Post Mortem Interval (PMI), or the time since death. Since most carrion-feeding insects, like blow flies, only colonize exposed or shallowly buried bodies, the coffin fly’s presence signals a different set of circumstances.
Coffin flies can colonize remains long after the initial wave of insects has departed. Their presence has been documented on bodies that have been buried for many years, with one case reporting colonization after 18 years postmortem. Finding these insects inside a sealed coffin or under a concrete slab provides forensic scientists with evidence of insect activity over an extended and protected period. Beyond forensics, the flies’ penetrating behavior makes them unusual pests. They can breed in deep, inaccessible places like broken sewer pipes beneath concrete foundations, making them difficult to eradicate in hospitals or food-handling facilities.