Hoverflies, belonging to the insect family Syrphidae, are commonly known as flower flies due to their frequent presence around blossoms. These insects display Batesian mimicry, sporting yellow and black bands that make them look deceptively like stinging bees or wasps. Hoverflies are completely harmless, possessing no stinger. Their existence is defined by a radical shift in diet, undergoing complete metamorphosis where the larval stage consumes entirely different food sources than the winged adult.
The Adult Diet: Fueling Flight and Reproduction
The adult hoverfly diet is strictly focused on floral resources, consuming nectar for immediate energy and pollen for reproduction. Nectar provides the necessary sugars to power their characteristic hovering flight. Their mouthparts are generally unspecialized, functioning to lap up nectar and harvest pollen from open-faced flowers.
Pollen consumption is particularly important for females, as the protein and lipids it contains are required for the maturation of their eggs, a process known as oogenesis. Some species also supplement their diet with honeydew, a sugary excretion produced by aphids.
The Larval Diet: Specialized Predators and Decomposers
The diet of the legless, maggot-like hoverfly larvae is highly varied, distinguishing them into two major ecological groups. Approximately 40% of all hoverfly species feature predatory larvae that are a significant natural control for soft-bodied agricultural pests. These larvae primarily consume aphids, but their prey also includes scale insects, thrips, caterpillars, and psyllids.
The predatory larvae, which are often translucent, hunt by lifting their tapered heads to sense prey and then seize them before sucking out their internal contents. A single larva can consume a substantial number of pests, often eating between 100 and 400 aphids during its two-week development period. Females strategically lay their eggs directly onto leaves near colonies of these pests, ensuring a readily available food source for the hatching larvae.
The second group includes the saprophytic or detritivore larvae, which recycle organic matter rather than hunting live prey. These larvae feed on decaying plant material, fungi, and sometimes filter-feed in aquatic environments. The well-known “rat-tailed maggot,” a larva of the drone fly (Eristalis tenax), is a prime example of this group, living in stagnant water or sewage.
These aquatic larvae possess a long, telescopic siphon at their posterior end, which acts as a snorkel to draw oxygen from the air while their body remains submerged in the nutrient-rich sludge. Other detritivores can be found living within the nests of ants or bees, where they consume debris or the eggs and young of the social insects.
Ecological Impact: Pollination and Pest Control
Adult hoverflies are recognized as the world’s second-most significant group of pollinators after bees, a consequence of their constant need for nectar and pollen. As they forage, pollen grains adhere to their bodies and are passively transferred between plants, supporting the reproduction of wild and cultivated flora.
The larvae of the predatory species provide highly effective natural pest control in both gardens and commercial agriculture. Their consumption of pests like aphids can suppress populations on crops by upwards of 70 to 100% when larval numbers are high. This biological control is so effective that certain hoverfly species, such as Eupeodes corollae, are commercially reared and released in greenhouses to protect high-value crops like melons and strawberries.