Hoverfly Lifecycle
Like butterflies and moths a hoverfly lifecycle starts with an egg. These eggs hatch into a larva before going through 3 stages of larval developmental each of incremental sizes. They then pupate, before metamorphosing into an adult. See diagram below.
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| Diagram showing the simplified hoverfly lifecycle |
A hoverfly egg can take 3 days to a couple of weeks to hatch. When the eggs are laid, they gain a waterproof coat called the chorion which prevents it from drowning or drying out, yet it is breathable to allow oxygen in and waste gases out. It is also, when laid, coated in a sticky adhesive ensuring the egg remains where the female chooses to lay it.
The larvae hatch into legless and blind maggots with no obvious head, identifiable by 2 fused breathing tubes sticking out its posterior, this being unique to hoverfly larvae.
Some larva can look like bird droppings a mimicry to avoid predation.
A larva that eats aphids is termed aphidophagus, they find their prey through chemosensory and touch. Using mouth hooks that can pierce the aphid’s skin, the larva also secretes saliva to hold its prey in place.
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A larva will eat 400 aphids on the way to becoming an adult. Some larvae are herbivorous and feed on plant material like bulbs or dead wood, the rest are detritivores feeding on decaying matter.
Volucella species lay their eggs into hornets and wasps’ nest where they hatch but stay hidden, staying dormant until autumn. When the workers of these Hymenoptera die off, they can become active and feast on the nest debris and deserted unprotected grubs. Gruesome but clever larva, avoiding becoming lunch themselves and being fed to the hosts young.
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| Greater Hornet Plumehorn (Volucella zonaria), Ransom Hoverfly (Portevina maculata) Narcissus Bulb Hoverfly (Merodon equestris) |
In the bulb specific hoverfly species such as Narcissus Bulb Hoverfly (Merodon equestris) and Ransom Hoverfly (Portevina maculata), the 1st larva tunnel into the bulbs and overwinter in a state of diapause (a state of suspended development allowing them to pause until more favourable conditions). In late winter they awaken, start feeding and growing, at the same time as the plants are mobilising their resources for growth in spring.
At the end of each larval stage, it sheds its outer skin, so that in the next stage it can grow larger. A process known as ecdysis.
At the 3rd Instar the larva must decide whether to go into diapause or switch genes on that will allow them to migrate, all before they pupate. Switching genes on to migrate allows them to develop bigger wings as an adult, along with other mechanisms enabling them to fly at higher altitudes. Click here to find out more about their migration.
Once the 3 larval stages are completed the larva pupates, most moving to a dry sheltered place to do this. I have often seen them on blades of vegetation, but those that overwinter will head for the soil/leaf litter. Hoverflies that are aquatic will climb out of the water to pupate, which is why it’s important that in man-made hoverfly lagoons, there are some twigs they can climb onto which lead out of the container.
The pupa, a teardrop-shaped case, is the hardened skin of the last larval stage. The larva will metamorphose into the adult and emerge when the environmental conditions are right.
The whole hoverfly lifecycle takes a minimum of 20 days to several weeks, from egg to adulthood although it can delay the onset of development and metamorphosis into an adult to a time when conditions suit best.
Summary
Below is an example of a very short hoverfly timeline, most are longer. |
| Diagram showing the timeline of a hoverfly lifecycle |
It summarises the key points about a hoverfly lifecycle and all the decisions made along the way, it’s not just a simple step from egg to adult.
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