Biological Control · Insect · Profile

Flies: Biological Control – Garden Critter of the Month

Flies at a glance

Occupation:
Predator, pollinator
Value to Gardener:
5/5 – Pest Controller and Pollinator
Danger to Humans:
2/5 – Most are harmless, some bite
Availability:
5/5 – They’ll arrive or you can buy some
Culex pipiens mosquito fly anatomy diagram
Basic anatomy of a fly, Culex pipiens mosquito
Quick Intro
Flies are seen as vermin and disgusting creatures. Although a large portion of flies are detrivores and parasites, most are active predators and excellent pollinators. Fly predators eat a large range of pest species and the pollinator species are valuable when bees are lacking.
Science Stuff
Flies belong to the order Diptera (Greek, di = two and ptera = wing) and includes crane flies, midges, mosquitoes and various fly species. Some species mimic bees in appearance, such as hoverflies and bee flies, and are important pollinators. This often leads to confusion between the two orders; therefore I again provide my little diagram to illustrate the difference between Hymenoptera (Bees, wasps and ants) and Diptera (Flies and mosquitoes). Hymenoptera have a narrow waist, whereas Diptera have their hind wings reduced to spoon-shaped halters used for balance in flight. Strepsiptera (twisted wing parasites) have the opposite, their forewings are reduced to halters and their hind wings are used for flight.
Fly vs Wasp, morphology, difference between fly and wasp, wings, halters, waist
Flies have large diverse niches, making use of all nature’s resources by being parasites, detrivores, fruitivores, pollinators and predators. Mouthparts vary from piercing-and-sucking to only a sucking proboscis. Chewing mouthparts are in some blood-feeding species. There are too many fly families to discuss, therefore, I will cover some of the more ‘garden’ important species:
Tipulidae (Crane flies, daddy longlegs, and leatherjackets):These are large, spindly flies with very long legs. They do not fly well and some are wingless. Larvae, known as leatherjackets, live in water or moist soil. Larvae feed on plant roots and may be destructive, whereas adults never feed. Example specimen in the diagram above.
Cranefly Nephtotoma species, emerging from pupae
Cranefly Nephtotoma species, emerging from under ground pupae
Culicidae (Mosquitoes): Best known for their blood-feeding (haematophagous) lifestyle and for transmitting diseases such as malaria, dengue fever, encephalitis, yellow fever and elephantiasis. In some species, both males and females feed on plant juices, in others, females need to take a blood meal in order to lay eggs. Males and females look identical, except males have bushy antennae to pick up on the buzzing sound of the females.
Aedes aegypti mosquito male and female E. A. Goeldi (1905) Os Mosquitos no Pará. Memorias do Museu Goeldi. Wikipedia
Aedes aegypti mosquito male (right) and female (left). Notice feathery antennae of male
Cecidomyiidae (Gall midges): Small, hairy flies that go mostly unseen. These flies will infest a specific host, to which they have evolved, through a process known as co-speciation. They cause galls formation on host plants. Adults are short-lived, whereas larvae are pests of millet, sorghum and rice.
Cecidomyiidae gall midge
Gall midge sp., Cecidomyiidae
Tabanidae (Horse flies, clegs, and deer flies): Sturdy flies often with iridescent eyes. Both males and females feed on nectar or plant juices, but females are also blood-feeding and inflict very painful bites. The females transmit surra or nagana to cattle and horses respectively, similar to sleeping sickness in humans, and also transmit the Loa loa eye worm to humans and monkeys.
Horse fly Tabanidae Tabanus sp.
Horse fly, Tabanus sp., Tabanidae
Asilidae (Robber or Assassin flies): Their robust build and prominent proboscis makes them easy to recognise. Many are hairy, aggressive and quite frankly scary – with an equal reputation as voracious predators of other insects. Adults are strong and agile fliers. Most larvae feed on detritus.
Robber fly with tessaratoma papillosa prey
Robber fly with stink bug, Tessaratoma papillosa, prey
Bombyliidae (Bee flies): Stumpy flies often covered in fuzz. They have long sucking proboscis and are important pollinators of many plant species. They bask in the sun and are active during the hottest part of the day, common in dry climates. They are graceful fliers and can rival the hovers in, well, hovering. Larvae are predators of insects or eggs.
Bee fly Bombyllidae Bombylius major Richard Bartz, Munich aka Makro Freak Wikipedia 2
Bee fly, Bombylius major, Bombyllidae
Syrphidae (Hover, Flower or Syrphid flies): These are the bee and wasp mimic specialists, all with black and yellow striped bodies – remember to check for the narrow waist when in doubt! They have an astounding precise suspended flight (hover) and can zip about quickly. Adults feed on nectar and pollen. Larvae occupy many different niches; some are predaceous on plant pests, whereas others (known as rat-tailed larvae) feed in mud, and every niche in between.
Hover fly flower red yellow
Hover fly
Tephritidae (Fruit flies): Easily recognised by their long ovipositor (egg laying organ), triangular heads and patterned wings. These flies are host specific and adults deposit eggs in important agricultural fruit plants. Larvae develop inside the fruits and feed on the flesh. Be watchful as some have ‘narrow’ waists, but look out for the halters, they are a dead give-away! Please see my Mediterranean Fruit Fly Pest post.
Euaresta aequalis Fruit fly Tephritidae
Fruit fly, Euaresta aequalis, Tephritidae

 

Habitat
Flies have diverse habitats and are common everywhere. Some larvae live in water, others on plants and some are soil-borne.
Robbers prefer to hunt in fairly open areas with little vegetation, so you will likely have them visit the garden rather than take up refuge.
Hovers are attracted to plants under attack by aphids – plants emit certain volatile chemicals when fed upon by pests that the hovers hone onto. The adults will buzz around the affected plant and promptly lay eggs on the leaves. Eggs hatch and the aphid-eating army munches away!
Bee flies? Just plant a basil – they loovvee the basil flowers! Provide some open areas in the ground or in your pots where they will make little burrows to overnight in. You will also notice that the bee flies make a lot more buzzing noise than bees. My garden is residence to many Woolly bee flies (Systoechus spp.) and they are adorable!
Woolly BeeFly (Bombyliidae, Systoechus sp.)
Woolly Bee Fly, Bombyliidae, Systoechus sp.
Woolly BeeFly (Bombyliidae, Systoechus sp.)
Woolly Bee Fly, Bombyliidae, Systoechus sp.
Diet
Robbers ambush bees, wasps, hornets, spiders, grasshoppers, other flies and many species of flying insects in flight. It stabs its prey with their short, strong proboscis. They inject neurotoxic (paralytic) and proteolytic (protein degrading) enzymes into their victims, and subsequently suck out the digested liquids – very gruesome!
Robber fly sp. The 'moustache' or mystax and occular fringes are visible in this species
Robber fly sp. The ‘moustache’ or mystax and occular fringes are visible in this species
Lots of small flowers, such as those from the Compositae or Asteraceae plant family (dill, fennel) will convince the adult hovers to stick around. The two regular visitors to my garden are, Allograpta fuscitibialis (I will refer to it as the Black thorax hover fly, due to a lack of a common name) and Eristalinus tenax (which I will just call the striped-eye hover fly).
Black thorax hover fly Allograpta fuscotibialis
Black thorax hover fly, Allograpta fuscotibialis
Black thorax hover fly Allograpta fuscotibialis
Black thorax hover fly, Allograpta fuscotibialis
Striped Eye Hover Fly, Eristalinus taeniops
Striped Eye Hover Fly, Eristalinus taeniops
Striped Eye Hover Fly, Eristalinus taeniops
Striped Eye Hover Fly, Eristalinus taeniops
Flies – last thoughts
Flies are unfairly defined as gross and need to be exterminated when the majority are misunderstood and beneficial to gardeners as predators of pest species and important pollinators. Seeing as they are so freely available, they make great supplementary pollinators (to bees) and effective biological pest control.
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