The adults are flower-eating and feed on nectar and pollen. They are highly active pollinators. There are three types of diet that the larvae can follow:

• the phytophagous ones which feed by mining the stems, roots or even the bulbs of plants
• microphagous types which consume micro-organisms in liquid environments
• zoophagous ones which prey on a range of insects, with a preference for aphids.

Aphidiphagous Syrphidae

Around 250 species of the subfamily Syrphinae and Melisiinae eat aphids. Some larvae are highly polyphagous such as Episyrphus balteatus which can consume several dozen different species. Others are conversely strongly specialized, like Tryglyphus primus which exploit only one species of aphid on mugwort, or Herengia heringi which can only develop on aphids galligenous.
The eggs are 1-1.5 mm long and laid one-by-one close to aphid colonies so that the larva can find its food easily. The total fecundity of females in the order of 500-1000 eggs and each larva eats around 400 aphids in its life which spans between 8 and 15 days. The larvae of Syrphidae can move around very easily and take advantage of any other plant. They take hold of the aphids, pick them up their support and suck out the whole of their interior tissues.

Morphology

Most Syrphidae show a characteristic wing venation with a vestigial vein, the vena spuria.

Biology

Four large types of biological cycle can be distinguished in the Syrphidae:

• The multivoltine species which overwinter at the adult female stage (Episyrphus or Scaeva). These species are the earliest to appear in spring
• The multivoltine species which overwinter at the nymphal and larval stages (Metasyrphus, Syrphus and so on)
• The bivoltine species: the larval diapause takes place in summer and winter (Melangyna)
• The univoltine species: only one spring generation and an obligate diapause of 9-10 months (Pipiza, Epistrophe, Platycheirus and so on)

Behavior

The adult can achieve 120 wing beats per second. This gives the ability for stationary flight which, combined with its often yellow and black livery, makes it easily recognizable. This aptitude in flight enables them to accomplish annual migrations, in massive numbers and specifically orientated at the end of summer and in autumn. The general direction of the autumn movements is southwards, in the Pyrenees or the Alps, where these Diptera can cross the high passes in their millions.

Conservation of Syrphidae populations

To reinforce their presence near croplands, flowering plants can be sown that attract them (to create flower covered strips); use can be made of plant types like Asteraceae or Apiaceae which provide a food source --pollen, determinant for the females’ fecundity. Well wooded landscapes are also favorable for Syrphidae as they harbour suitable sites for overwintering and an alternative source of food.