Blowflies, which belong to the insect family Calliphoridae, are commonly known by their distinctive metallic sheen, often appearing as bluebottles or greenbottles. These insects play a significant role in nature as some of the first organisms to arrive at and consume decaying organic matter. A female blowfly deposits her eggs in clusters. The study of blowfly eggs and subsequent larval development is a predictive tool in forensic science, providing biological evidence used to estimate the time since death.
Primary Locations: Decaying Organic Matter
The primary stimulus for a female blowfly to lay her eggs is the odor of decomposition, which signals a protein-rich and moist environment necessary for her offspring. The most common and potent attractant is carrion, or the decaying flesh of dead animals, which serves as the initial food source for the newly hatched larvae. Blowflies are equipped to detect the volatile organic compounds released by a carcass from distances up to 16 kilometers away. This rapid detection ensures the larvae, known as maggots, have immediate access to nutrients upon hatching.
Beyond wildlife carrion, blowflies frequently target other forms of proteinaceous waste found near human habitation. This includes spoiled meat or fish, which can lead to sudden infestations in homes, and improperly sealed outdoor garbage receptacles containing food scraps. Animal feces and manure also represent suitable breeding materials, as they provide both the moisture and organic matter required for the maggots to complete their growth cycle.
Specific Placement on the Source Material
Once a suitable decaying resource is located, the blowfly is highly selective about the precise location for egg deposition, favoring sites that offer immediate warmth, moisture, and protection. Eggs are almost always found concentrated around the natural orifices of a carcass, such as the eyes, nose, mouth, and anus, as these areas are typically the most moist and accessible for larval penetration. In the case of a dead body, the female will seek out any open wounds, as damaged tissue provides an entry point to the moist internal tissues that the young larvae cannot otherwise penetrate.
The eggs are often laid in protected clusters deep within crevices, folds of skin, or beneath objects, which shields them from environmental threats and predators. On a deceased organism, this micro-placement strategy includes areas where the body is pressed against the ground, creating a dark, humid pocket. This placement ensures the eggs do not dry out, which is a major cause of egg mortality.
Environmental Conditions Guiding Egg Laying
External environmental factors significantly influence the female blowfly’s final decision on where and when to deposit her eggs. Temperature is the most influential variable, as the fly’s reproductive cycle is highly dependent on warmth for both egg-laying and larval development. While some cold-tolerant species, such as Calliphora vicina, may lay eggs at temperatures as low as 10 degrees Celsius, warmer temperatures generally increase the probability of egg-laying. The female often seeks out protected, warmer microclimates within a food source to maximize the speed of the life cycle.
Moisture is another factor that heavily guides egg placement, as the thin, delicate eggshell is highly susceptible to desiccation. High humidity is therefore preferred, which is why eggs are often found in shaded areas or deep within a substrate rather than on exposed, sun-baked surfaces. Blowflies also generally avoid direct wind and strong sunlight, preferring sheltered spots that offer a barrier against harsh conditions that could dry out or dislodge the vulnerable egg clusters.