Syrphidae (hoverflies)

Family: Syrphidae (hoverflies)

Life > Eukaryotes > Opisthokonta > Metazoa (animals) > Bilateria > Ecdysozoa > Panarthropoda > Tritocerebra > Phylum: Arthopoda > Mandibulata > Atelocerata > Panhexapoda > Hexapoda > Insecta (insects) > Dicondyla > Pterygota > Metapterygota > Neoptera > Eumetabola > Holometabola > Panorpida > Antliophora > Diptera (flies) > Brachycera > Muscomorpha > Eremoneura > Cyclorrapha > Aschiza > Syrphoidea


Eristalis tenax (subfamily Eristalinae), an introduced species to South Africa. [photo Hamish Robertson]	Eupeodes corollae (subfamily Syrphinae) on daisy in mesic mountain fynbos. Also introduced to South Africa.[photo Hamish Robertson]

Eristalodes sp. [photo Hamish Robertson]	Syrphid feeding from daisy flower in Cape Town garden.[photo Hamish Robertson]

Subfamilies

Eristalinae

Microdontinae

Syrphinae

Introduction

Hoverflies or syrphids (scientific name: Syrphidae) are one of the most eyecatching flies. Almost everybody has seen a hoverfly either in natural habitats or in parks, gardens or even on balconies. Many species are more or less as big as or even bigger than houseflies and have yellow or orange patterns (spots or bands) on their back (called abdomen). At first glance, many of them can be mistaken for bees or wasps. Syrphids, however, are absolutely harmless. They cannot sting nor bite.

Hoverflies are not only nice looking insects with an interesting behavior (hovering!) but also important pollinators. The larvae of many species act as effective predators of aphids and other insects. Other syrphid larvae feed on a wide range of dead organic matter and act as decomposers. As such, they make the minerals in the dead organisms available for the living plants again.

Behaviour, life span

In South Africa the adult syrphids can be observed throughout the year. The best season to watch them is spring and summer. Then the adult flies find sufficient nectar and pollen in the blossoms to feed on.

All hoverflies are diurnal. They are most active in the morning and in the afternoon when the sun is shining. At noon, temperature is often too high for many insects. They would risk to loose too much water by transpiration and get over-heated. The flies try to endure unfavorable conditions (e.g. cold, rainy, stormy or hot weather) by sitting motionsless on low plants in thick vegetation, under leaves and at other protected places.

Good places for hoverfly watching are sites with lots of suitable flowers and egg laying sites. These are also the localities where males and females mate. In some species the males just sit on a leaf, twig or stem and watch their environment waiting for females. Others hover, ready to mate or patrol those areas which females are laying eggs or feeding.

An adult fly lives just some days or a few weeks. It has many enemies: wasps, spiders, birds, lizards, small mammals, etc. In contrast, the life span of the larvae may last up to two (or more?) years. Health and life span of larvae and adults can be influcenced by parasites and parasitoids. If the physical (weather!) and biological (nutrition!) conditions are good several species complete their life circle (egg - 3 larvae instars - pupa - adult) within about one month.

Habitats

Hoverflies can be found in every biotope but not in deserts. Each species tends to prefer a certain type of habitat and is limited to a distinct range within the country. There are relatively few species with broad habitat tolerances that enable them to be distributed throughout southern Africa.

In general, within a genus the needs and behavior of the species are similar. As a result, one tends to associate certain genera with particular habitats. For example Chrysogaster, Eristalinus, and Mesembrius (all with aquatic or semi-aquatic larvae) are typical found in wetlands, many tiny Paragus species live in grassland whereas species of Baccha, Melanostoma and Xylota prefer woodlands.

Within a given habitat the hoverflies have an irregular distribution. Some prefer the low vegetation (like Melanostoma and Paragus), others can be observed in the tree canopies (like Mallota and Spheginobaccha). There are also differences in the horizontal distribution of the adults at a site since important structural components like certain flowers or egg laying sites cannot be found everywhere within a habitat.

A considerable number of species live in gardens and public parks. The more attractive flowers (e.g. Asteraceae, Brassicaceae, Ranunculaceae and Rosaceae) there are growing in a garden, the more adults there are to be observed.

To increase the number of species that reproduce in the garden it is important to provide egg laying sites (e.g. ponts with aquatic and dense bank vegetation, compost heaps and areas where weeds and grass are allowed to grow). Active gardening like mowing and hacking may distroy attractive larval habitats. Obviously, insecticides should be avoided.

As a result a garden with a great number of indigenous syrphid species is not always that type of garden of which a traditional gardener would be proud of. However, a little "wilderness" in a hind corner of the garden may serve as a refugium for several syrphids without reducing the "beauty" of paradise too much.

Distribution in South Africa

Hoverflies can be found all over the country between the sea-shores and the mountains. In total, there are at least 180 species recorded from South Africa. The number of species declines from the northeast to the southwest. However, some species have only or predominately been found in the Western Cape.

Almost all of the South African species are limited to the African continent. Some are even exclusively known from South Africa. However, this may be a result of poor research in neighbouring countries. A small number of species was unintentionally introduced from Europe or / and Asia by man (e. g. Eristalis tenax and Eupeodes corollae).

Ecology

Adults

The adults mainly feed on nectar and pollen. The females must consume pollen since they need the proteins and amino acids of the pollen for maturation of their eggs. Nectar has only a small amount of these substances but much sugar. It is the fuel for the flies, enabling them to fly and hover actively.

Being regular visitors of flowers, hoverflies are important pollinators of various plants including vegetables and fruit trees (e.g. Asteraceae, Brassicaceae, Rosaceae). The flies select the flowers mainly by their colours. They also recognize ultra-violet (UV) marks on the blossoms.

Most of the adults have short mouthparts. Therefore hoverflies prefer flowers with a simple anatomy to get easy access to pollen and nectar. Many of these blossoms are white or yellow. Apparently this is one reason why hoverflies quite often prefer white or yellow as a colour (this can be used for recording syrphids and several other insects by capturing them in yellow or white pan traps).

Larvae

Compared with the adults, the nutrition of the larvae is more diverse. Three large ecological groups can be distinguished: predators, miners and decomposers (living on dead organic material - saprophagous larvae).

All species of the subfamily of Syrphinae have zoophagous larvae. Their main prey are aphids (greenflies). The larvae of Microdontinae are associated with hymenopterans. The Microdontinae larvae are supposed to be zoophagous living in ant nests.

Eumerus and Merodon larvae are plant-eating (phytophagous) miners. They live in/at dead bulbs (in fact at least some may feed on fungi in the decaying tissues). The larvae of the remaining eristaline species are saprophagous organisms; they live in various habitats (running or stagnant water, mud, compost heaps, rotten wood etc.) feeding on dead organic substances.

Not many details are known about the ecology of the African hoverflies. In many species the instars are still to be discovered (and described). However, some widely distributed species (e.g. Eristalis tenax and Eupeodes corollae) have been investigated in Europe and Asia. It can be assumed that these species have a similar ecology in South Africa. But in general there is a great need of specific studies of the hoverflies and their ecological importance in (South) African habitats. But please note: before starting a scientific study for example in the house garden one should be sure about the identity of the observed syrphids; some common species show very little differences in their appearance but may considerable differ in their habits and ecology.

See life cycles of Eupeodes corollae and Eristalis tenax.

Acknowledgements

The author would like to thank (the late - ed.) Dr Brian R. Stuckenberg (Pietermaritzburg) for many valuable discussions on South African Diptera and Dr. Adrian C. Pont (Oxford) for improving the English text of the manuscript.

Text by Werner Barkemeyer