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.