Pyrgota Fly – Pyrgotidae sp.

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Pyrgota Fly – Pyrgotidae sp. 

These are very nondescript flies and being darkly coloured usually go unnoticed, plus this is not helped by their largely nocturnal activities. However, they are very unusual flies by producing parasitic larvae that eat adult scarab beetles alive and then pupate inside their exoskeleton. As most scarab beetles are only active at night and spend the day buried in the ground; it is why the Pyrgota Fly is also nocturnal, although occasionally it will feed from flowers during the day. 

A characteristic of scarab beetles is the very hard elytra (the hardened forewings that protects the more fragile flying hind wings and the abdomen), a feature which makes life difficult for these flies to pierce the abdomen and deposit their egg. This problem has been solved in several ways by this fly and evidenced by its worldwide distribution with at least 330 species (Australian Faunal Directory). 

Some Australian Pyrgotidae species are known to just perch on the back of a beetle and thrust its ovipositor beneath and into the “intersegmental membranes, or through the anal opening” (1). Others will alight on the back of a beetle to make it fly and when it lifts its elytra in order to do so, will insert “the ovipositor through the thin exposed integument of the abdominal dorsum.” (1). However the one I imagine most challenging, is when the Pyrgota fly intercepts a flying beetle as described by the USDA, and with ‘a lightningswift jab with her stilettolike ovipositor and thrust an egg inside the body of the beetle.’ (2). 

The scarab beetle will continue to feed at night and then rebury herself during the day, but as her strength fails due to the activity of the larvae inside her, she eventually will remain in her burrow. During this time the fly larvae will have hatched within a few days and immediately began to consume “all the body fluids and fat,” after which it “boldly attacks the muscles and vital organs.” (2). The beetle dies after a week or two and the larvae pupates within the exoskeleton, to emerge as a fully formed fly the following spring. 

The local Pyrgota Fly has wings that are clouded brown with pale transparent flecks and extend 25% further than its total head/body length. The species above including the wings, were 2 cm (3/4”) in total length. These largely nocturnal flies are attracted to house lights, which is probably the only way most people will encounter them, and for this reason they are also known as Light Flies. 

The Pyrgotidae family belongs to the Tephritoidea superfamily. 

(1).  http://www.faculty.ucr.edu/~legneref/identify/pyrgotid.htm

(2).https://docs.google.com/viewer?a=v&q=cache:Q_1HGI9OTyQJ:naldc.nal.usda.gov/download/IND43894233/PDF+Pyrgota+au&hl=en&gl=au&pid=bl&srcid=ADGEEShHjh31gd1hW9iqMY-c7ZOSeGRzXTu8mekgKmCbChq2F4B7v2ZPsijmHKRDq6g5OcTMaC1GxHq-MUA5Ddx7xs1sKgPJLNspJqTZiC5KwDLa0VTM2Ju1fXVZcEthNjSwoVDU9ifa&sig=AHIEtbTbNo2g6C0vSYnc4JRuBWUAGyo-vA

Tangle-veined Fly - Trichophthalma sp.

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Tangle-veined Fly - Trichophthalma sp.

The Tangle-veined Fly belongs to the Tabanoidea Superfamily that includes such nasties as the March and Horse Flies.  However in the Trichophthalma family Nemestrinidae, instead of feeding on blood, feed on flowers via a long sucking proboscis.  They are often seen hovering with rapid wing-beats whilst feeding, or will hover in the same spot for some time before darting away only to quickly return.  This activity and their solid build suggest a Bee Fly, but with those flies the wings are much longer and they don’t have an extended point to their abdomen.

Also like Bee Flies, Tangle-veined Flies are softly hairy, plus their larvae are parasitic on various insects including grasshoppers, so both play an important role regarding insect control.  The pointy end of the female abdomen contains a retractable ovipositor (for egg-laying) and is probably used to favourably place their eggs on or within an insect host.

The wing venation is quite congested compared to most fly wings, which is how they get their Tangle-veined common name.  Above, the fly is feeding from a common shrub of coastal calcareous sand, Logania vaginalis that is detailed in the Esperance Wildflower Blog (located top right).  These flies are not an evolutionary new-comer but have a long linage, as they also occur in South America to suggest a Gondwana origin.

Asilidae - Asilinae sp. - Robber Fly

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Robber Fly - Asilinae sp. - Asilidae

Worldwide there are thousands of Robber flies in the Asilidae family and in Australia, the Australian Faunal Directory lists 360 species with other authoritative sources quoting more than twice that number. So whatever the figure, there are a lot of them. Australian Asilidae are divided into 4 subfamilies with Asilinae being the largest. As a general rule, these subfamilies can be determined by the structure of their antennae with Asilinae having a fine terminal projection (antennal style), others are more feather-like, or uniformly thick, or have no projection at all.

Around Esperance I have not noticed many species, which is either just me, or that most of these robber flies prefer forested areas, although the one shown above is reasonably common. Asilidae are amongst the largest flies, with some possessing a 7.5 cm (3”) wingspan. The one above although impressively large, had only a 4.5 cm (a little under 2”) wingspan and a head/body length of nearly 3 cm or a little over 1”. However to most insects it would be terrifyingly large, as being predatory they will attack almost any flying insect, some larger than themselves.

Robber flies will perch and wait for an insect to fly past; it will capture it in flight grasping it in its strong legs. The exterior of the prey will be pierced with its sharp proboscis and injected with powerful enzymes to reduce the insides to a mush, then sucked out by the fly, leaving little more than an exoskeleton. Locally the above robber flies were most active from December to February.