Hover flies

bee-like fly in mid air
Hover fly earning its name

Hover flies are common in our garden except in the dry season and we are beginning to see them again now that the humidity and temperature are rising. Their common name comes from their distinctive, odd-looking habit of hovering in one spot, darting forwards or sideways, and then hovering again; it is behaviour which make mid-air photos feasible and that’s what you see above.

We see at least a dozen species around our garden (photos here, on flickr) and Graeme Cocks has identified twice that many around Townsville, out of about 6000 species worldwide. Most of them are bee or wasp mimics but appearances are, as so often, deceptive: they are all completely harmless.

My photo shows a Common Hover Fly (Simosyrphus grandicornis, Syrphidae) near Pentas leaves. As I watched, it landed on a seed-head and then took off to fly down into the base of a nearby flower-head and lay some eggs:

bee-like fly
Female hover fly on a Pentas seed-head
fly beneath pink flowers
Hover fly laying eggs on the base of Pentas flowers

That made me wonder about the life cycle because I had always (vaguely, rashly) assumed that the larvae would feed on decaying matter just as the larvae (maggots) of the most familiar flies do. The Australian Museum’s fact sheet on the family told me, “Hover flies are also called flower flies because they are commonly seen during warmer months hovering among flowers, feeding and mating. They pollinate many plants and help keep aphids under control.” That made me look further. Wikipedia to the rescue:

Hoverflies are important pollinators of flowering plants in a variety of ecosystems worldwide. Syrphid flies are frequent flower visitors to a wide range of wild plants as well as agricultural crops and are often considered the second most important group of pollinators after wild bees. However, there has been relatively little research into fly pollinators compared with bee species.
Unlike adults, the maggots of hoverflies feed on a variety of foods; some are saprotrophs, eating decaying plant or animal matter, while others are insectivores, eating aphids, thrips, and other plant-sucking insects. This is beneficial to gardens, as aphids destroy crops, and hoverfly maggots are often used in biological control.

Our Common Hover Fly is one whose larvae are aphid predators, so laying eggs on Pentas makes perfect sense. Brisbane Insects describes a closely related species (their Ischiodon scutellaris is now Simosyrphus scutellaris, putting it in the same genus as mine) as doing the same on hibiscus plants, and provides photos of the larvae.

I’ve got to say, though, that I find the adult flies more attractive than the grubs. Here’s one sipping nectar:

fly on white flower
Hover fly feeding on a basil flower

A very small drama on Castle Hill

Castle Hill from the Magnetic Island ferry
Castle Hill from the Magnetic Island ferry

Castle Hill is an immense mass of pink granite rising above the city. Beloved by tourists, joggers and landscape painters, it is a challenging environment for wildlife because the soil (where there is any) is so thin. Rainwater drains off almost instantly, so the vegetation struggles to survive and there aren’t many herbivores to feed the carnivores. Nevertheless, on Sunday I spent almost an hour in a little patch of open scrub near the summit, watching to see what was around, and was well rewarded.

There were grasshoppers, butterflies (Blue Tigers, Migrants, Crows and a few others), a couple of bee-flies, a baby mantis and lots of ants (links here take you to these insects on my flickr photostream), but the spiders drew my attention. There were odd little patches of silk in a few seed-heads of the tall grass and I pulled one apart to find a small pale-gold spider, while a similar but bigger patch in a knee-high sandpaper fig tree was home to what looked like a whole family (a female guarding her egg-sac and a smaller adult which could have been the male) of grey-brown spiders. A slim grey spider with enormously long legs appeared on the trunk of a poplar gum and wandered off again, and I watched the later stages of a deadly attack on one spider by another.

The attacker was a jumping spider (Salticidae, perhaps a Sandalodes) and its prey was a Lynx (Oxyopes macilentus). Both are predators, but the Lynx is an ambush hunter, typically waiting for prey to come within reach, while jumping spiders are roving hunters. In this case it looks like the jumping spider, the larger of the two, had chanced across the Lynx and lived up to its name; the Lynx offered very little resistance to its larger attacker.

How big are they? Not very big at all: perhaps 11 mm and 7 mm. If I hadn’t chosen to sit quietly and look around,  I wouldn’t even have noticed them in the grass.

two spiders
The jumping spider already has the advantage
two spiders
Nearly over. The Lynx has lost a couple of legs
two spiders
It’s easy to feel sorry for the loser

A prowl around my garden

I went for a prowl around my garden on Friday morning, camera in hand, to see what bugs were around. My intention was to take photos of everything, whether I already had photos of it or not, as a way of documenting (and reminding myself) what is active at this change-of-season time.

In the event I missed a few on purpose and a few because they were too quick for me but ended up with presentable shots of 25 species. I uploaded them all to Flickr and they can be viewed as a slideshow here (if it doesn’t work for you, click here to go straight to Flickr). For information about them, enter full-screen mode and click “show info”, or click on the photo to go to the Flickr page (new window).

What did I miss?

  • I saw many of the butterflies I mentioned in my previous post but didn’t bother chasing them;
  • a hover-fly, a brown paper wasp and a black and yellow mud-dauber wasp escaped before I could get a shot;
  • I could easily have taken photos of St Andrew’s Cross, Spiny and Silver orb-weaving spiders but I know I could do that any time;
  • I didn’t photograph all the species of small dark flies I saw, because there are too many and they are too similar; and
  • By restricting my collection to that one-hour prowl I missed the Eurema butterfly, Giant Grasshopper, Neon Cuckoo Bee and swarm of tiny bees I saw later in the day.

There’s a lot of life in a garden, if only you look!

Predator

As I said a few months ago, “When I started taking a real interest in invertebrates, flies were the group that surprised me most. Time after time, something I thought was a wasp or bee, even a dragonfly, turned out to be a fly.” Here is one that lives a dragonfly lifestyle, an active, agile aerial predator. It is a Robber Fly, Asilidae. 

Robber fly and bee
Robber fly, Asilidae, and Blue-banded Bee, Amegilla sp.

It is quite large by insect standards, nearly as big as a dragonfly but much more heavily built, and its strength allows it to take much larger prey. This one has caught a Blue-banded Bee (Amegilla sp.) and is perching on a Pentas stalk to consume it. I have also seen them with Soldier Flies (almost bee-sized) and, amazingly, one with a Cicada as big as itself.

There’s a good article about Robber Flies on wikipedia if you would like to know more.

Nocturnal visitors

I was thoughtless enough to leave a window open and a light on in my study on Wednesday evening and by the time I noticed, there were dozens of little bugs around the light and resting on the ceiling. There were several green lacewings, at least one brown lacewing, a creature I thought was a katydid but turned out to be a cricket, some bugs which looked like small pale mosquitoes but were non-biting midges, many tiny moths and flies, and miscellaneous others. Here are some of them.

cricket looking like brown grasshopper
Cricket (Gryllidae, perhaps Amusurgus sp.), about 12mm long not counting the antennae (click for larger view, as usual)
green lacewing
Green lacewing (Neuroptera, Chrysopidae) resting on ceiling
midge
Not a mosquito but a non-biting midge (Chironomidae). Love the feathery antennae!
midge
Another non-biting midge, Chironomidae
orange and black fly
This looks like it could be a wasp but it is a fly (Diptera, Plecia sp.)

These five all look roughly the same size on screen but in real life the midges are only 4 – 5 mm long and the others are two or three times their size.

The room has a resident population of spiders and they benefited from the influx of prey. The fly here is not a house fly but about half that size, so the spider is correspondingly minute.

spider and fly
Daddy long-legs with an incautious fly.

What’s around – mid August 2012

mating craneflies
A mating pair of Tiger Craneflies, Nephrotoma australasiae. Legs everywhere!
The sexes are very similar but the female (at top of this picture) is more heavily built.

The total rainfall since my previous mid-month summary is exactly zero, and the relative humidity has been very low, too: below 20% at 3pm every day for the last two weeks, for instance. Temperatures have consistently swung between 8 – 10C overnight and the mid twenties during the day. Cool and dry is not what the bugs like and I’m beginning to think of them as being in ‘maintenance mode’, just ticking over and waiting for some warmth and moisture.

The paperbark is flowering, as I mentioned a few days ago, and so is the mango tree. The Macadamia is almost ready to follow suit, and so is the Poplar Gum. Each of these trees attracts its own group of nectar-feeders. The birds love the paperbark (as I mentioned in my previous post) and the poplar gum, but are not particularly fond of the other two. The honey bees don’t seem to care for the mango blossom but love the other three, so that pretty much leaves the mango to the butterflies, the flies (mainly hoverflies), wasps and native bees.

large hoverfly on mango blossom
Hoverfly on mango blossom

I’m seeing …

    • Quite a lot of little orb-weaving spiders – Silver Orb-weavers (Leucauge granulata), Spiny Orb-weavers ( which I now believe to be Gasteracantha sacerdotalis rather than Austracantha) and St Andrew’s Cross spiders; also quite a lot of jumping spiders (Salticidae), some Lynx, and a few flower spiders.
    • Hoppers and their nymphs, which often become food for the above.
    • Butterflies: reasonable numbers of Junonia and Eurema and grass moths; very small numbers of everything else but including Migrants, Skippers, Melanitis leda and recently one visiting Orchard Swallowtail.
Giant grasshopper on variegated leaves
Giant grasshopper on giant variegated lily
  • Diptera (Flies): Long-legged flies (see bottom of this page), Hoverflies (see at left) and Blowflies, with occasional soldier flies and craneflies (above) and – still – mosquitoes.
  • Hymenoptera (wasps, bees and ants): occasional little wasps including paper wasps (though no nests that I’m aware of) and a very few mud-daubers; some native bees again recently after a gap of a few months; the usual small ants and a slowly-growing green-ant colony.
  • Others: a few Giant Grasshoppers; a healthy population of cockroaches in the compost bin; but no mantises (although saying that usually ensures I will see one in the next day or so).

Same time a year ago

Microfauna (3) flies

When I started taking a real interest in invertebrates, flies were the group that surprised me most. Time after time, something I thought was a wasp or bee, even a dragonfly, turned out to be a fly. As the Queensland Museum says,

Flies belong to the Order Diptera. In Australia there are almost 7500 described species in 100 families. … Many sorts of insects are called flies but “true flies” are a distinct group of insects which have only one pair of wings, unlike the caddisflies, scorpion flies, mayflies and butterflies that have two pairs of wings. … True Flies are found everywhere, and include delicate craneflies, mosquitoes, and midges, as well as robust horseflieshouse flies and blowflies. …

If the stereotypical response to spiders is “Eeek!”, the response to flies is “Yuck!” Both responses are unfair, if only because of the enormous diversity of these families: many, probably most, of them are not at all scary and not at all disgusting in their habits. The QM again:

Biting, blood-feeding flies such as mosquitoes, midges, horseflies and blowflies are able to transmit diseases to humans and domestic animals. … But most flies are not pests, most are important decomposers of plant and animal matter.

This page doesn’t include any of the Diptera that we don’t usually think of as flies, e.g. mosquitoes and midges. None of them are as big as a house fly, which is 5 – 8 mm long, and most of them, like most of my tiny spiders and miscellaneous other tiny insects posted recently, are 2 – 5mm.  I don’t know much about some of the species pictured here, because they are so small they have escaped even my notice until recently, but I will give what information I can.

fat red fly with barred wings
Signal fly, Platystomatidae, Rivellia sp., about 4mm long.
slim brown fly with long legs
About 6-7mm long but very slim, probably a crane fly, Tipulidae. Resting on a Dianella lily.

Crane flies often don’t feed at all as adults, living only to breed. When they do feed, they feed on nectar. Bigger relations of this little one are very common, and here is a picture of one sipping from mango blossom.

Squat black fly with red eyes
Only about 2mm long but built like the proverbial Mack truck. Why? I don’t know. What is it? Ditto.
Colourful fly
2-3 mm long and strikingly coloured, and that’s about all I know.
metallic green fly with black-banded wings and abdomen
A Long-legged fly, Dolichopodidae, probably Austrosciapus connexus, about 4mm long.

The Long-legged flies are tiny counterparts to dragonflies in that they are swift, agile aerial predators. They are common in my garden year round but are very difficult to photograph because they are so fast – they usually jump at the beginning of the flash and show up as a blur on the edge of the picture. Dragonflies are not true flies, of course (they have four wings). One small indication of the diversity of our flies is that there are almost as many Australian species of this one family (about 320) as there are of all Australian dragonflies.

Most Dolichopodidae that I see are metallic green or gold, but some are less showy:

Long-legged grey fly
Dolichopodidae again, a little larger than the one above.

More about flies: CSIRO entomologyWikipedia/FlySOWN/Diptera.