Text:
Anna i Lech
Krzysztofiak
Photos:
Lech Krzysztofiak
Maciej
Romański
Drawings:
Anna Krzysztofiak
Webdesign:
KAJA
2004
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Dipterans
A hover fly of the Syrphidae family. |
Dipterans are a relatively recent insect order: the oldest known specimens go back to 150 million years, to the Jurassic period. Currently ca. 90 000 dipteran species have been recorded, and out of this number more than 6 600 have been found in Poland. 200 dipteran species have been found in the Wigry
National Park, whereas only hover flies (Syrphidae) have been studied extensively.
Halteres
– reduced second wing pair (p). |
The food source of dipterans is very varied. Some of them, e.g. hover flies, feed on flower pollen and nectar, others, e.g. Asilidae, are predators
while still other species, for example horse-flies (Tabanidae), feed on the blood of vertebrates. Many dipterans parasitize other insects, birds and
mammals. For example, bee-flies (Bombylidae) parasitize the nests of bees and solitary wasps, flesh-flies (Sarcophagidae) live in the bodies
of insects and mammals, whereas tachinid flies (Tachinidae), live in the bodies of other insects.
The common feature of dipterans is the absence of the second pair of wings which have been reduced to the so-called halteres. Frequently their mouthparts
are of the sucking type enabling liquids to be used as food sources (nectar, juices, blood or dead tissue).
A robber fly (Asilus sp.) can be seen
when it lurks on flowers.
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In the development of dipterans there is holometabolous metamorphosis, their larvae are soft, worm-like with or without a distinct head region. Some
dipterans are viviparous and they are delivered as developed larvae. Dipterans reproduce very intensively, some species have several (3 to 10) generations
in one season. The house fly may have even 20 generations in one year.
Predaceous dipterans are represented amongst others by robber-flies (Asilidae). They are efficient predators hunting for various insects (other
dipterans and hymenopterans – including the honey bee), catching them in flight with their long limbs. Not only the adults, but also the larvae are
predators.
A laphriine fly (Laphria sp.) lurking for prey. |
There are many cases of mimicry (adaptation of the appearance to other animals, mainly as a protective measure) in dipterans. Bee-flies (Bombylidae
), resemble bumble-bees, they flight very efficiently and they can hover in the air. The adults feed on flower nectar, while their larvae parasitize the
nests of bees, wasps, beetles and other dipterans.
The ant fly (Microdon eggeri): male and female;
their larvae live in anthills. |
In forest communities of the park, especially in bog coniferous forests, parasitic dipterans of louse-fly (ked) family (Hippoboscidae) can be found.
They have a number of adaptations to living on the bodies of mammals and birds: a hard, flattened body, shortened antennae and strong limbs ending with
little claws and adhesive pads. The most common species include the deer ked (Lipoptena cervi) which sheds its wings when it finds the host and
sucks the blood. At the end of summer and in autumn they can also also be a nuisance to people walking in the forest.
Hover flies (Syrphidae) are the best studied dipterans in the Park. They have beautiful body colours, often resembling bees or wasps at a first glance.
They usually occur on flowers, where they feed on pollen, nectar and honeydew. Some larvae of hover flies are saprophages (they feed on dead organic
matter), while the other parasitize nests of bumble-bees, wasps and ants: another group are predators, hunting mainly for aphids and scale insects. Hover
flies are very good fliers – they hover in one position in the air for even a relatively long time.
The European rosette gall midget
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The presence of some dipteran species can be revealed by characteristic rose-like excrescences (gallnuts) located at the peaks of willow branches. The
formation of the gallnuts is related to the development of the European rosette willow gall midge (Rhabdophaga rosaria), belonging to gall midges
family (Cecidomyidae). When laying eggs, the female punctures the willow shots and injects a specific substance which causes leaves to degenerate
and create a gall-like structures providing protection for the larvae.
The mosquito and its larva.
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Dipterans from the Tabanidae family are a nuisance to man and animals. Their females feed on blood, biting painfully the skin of the attacked prey.
The horse-fly (Tabanus bovis) – largest representative of this family in Poland – reaches up to 2.5 centimetres.
The blood-sucking dipterans include the common gnat (or mosquito) (Culex pipiens) whose larvae develop in stagnant water.
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