Hover flies, humble members of the Order Diptera

Flies, members of the insect order diptera, are burdened with the bad reputations of some of their members. Mosquitos are flies; tsetse flies are flies; house flies are flies. But there are around 80,000 species of diptera worldwide, and the life histories of these creatures are varied and not all evil or even annoying. Many of them are what we humans regard as beneficial. (Bear in mind that on a happy day I consider house flies beneficial in that they provide food for spiders.)

During summer, the many species of hover flies (family Syrphidae) visit flowers to feed on nectar and pollen. They are one of the most prolific pollinators, but are often taken for bees, which they mimic in color and form. Here are a few of the species I observed in the past few weeks.

Syrphids may look something like bees, but they distinguish themselves by (among other things) having two wings instead of four, shorter antennae, and the ability to hover motionless. You'll see bees that may be small like syrphids, but they dart or bumble from flower to flower while the flies exhibit amazing aeronautic abilities.

Notice that two of these photos show the fly with the same flower---tanacetum vulgare or common tansy. It's a magnet for bugs of all sorts but especially flower feeders.

Syphid fly larvae (the stigmatic "maggot" is the term for fly larvae) eat aphids, so whatever you can do to encourage syrphids to like your garden or yard will pay off in free aphid control.

Really pretty spider web

Nice work by this young spider; probably Neoscona oxacensis, the common orb weaver. Notice how fine and close together the strands of silk are: this web was about 18" in diameter.



On the other hand, this other spider's lair isn't so pretty at least by our standards: No geometry, no gossamer sheet wafting in the slightest breeze. Just a down and dirty trap all stuck together with dead rose leaves and withered petals, prey carcasses, old wadded up silk, all providing a hideout for its occupant . . . whose name I do not know.

Mystery pest solved

So I got some batteries for my flashlight, and after nightfall ( 9 or 10 ish) I approached the privet hedge, scene of previously unsolved leaf chewing. I heard what sounded like small dry things--dead leaves I thought at first--cascading down the shrubbery. Scanning the hedge, I quickly found the cause of the leaf damage: a small, dark reddish brown beetle with corrugated wings (elytra, actually, the thickened forewings typical of beetles) was chewing a typical pit in the margin of a leaf. She had a slightly elongated snout--aha, a weevil then! I reached out to grab her; she froze, lost grip of the leaf and tumbled dryly to the ground. What I had taken for leaves falling must be weevils taking evasive action. So it's likely they hide on the ground during the day, since the death drop from 6 feet up in the shrubbery would be really impractical if they didn't.

I had a short look around the rest of the garden that night, and I noticed this little weevil posing nicely on top of a tansy flower, proving whatever she is, she does not limit her nighttime activities to the privet hedges.



Next day I had a look under some rocks. Sure enough, second one I turned over had several weevils under it. They weren't moving; I could pick one up and it made no attempt to get away, or even wake up.


Insects of the Los Angeles Basin offers a very convincing description of the strawberry root weevil, Otiorhynchus cribricollis: a dark reddish brown, short snouted weevil about 1/4 inch long which is flightless and eats leaves (including privet) at night. The mystery pest is probably this species (although my specimen is larger, about 5/16 inch), or a closely related root or vegetable weevil. Interestingly, these weevils are parthenogenic, meaning they produce offspring (all female) without mating.

Otiorhynchus cribricollis is a bonafide pest, and you can get more information about its control at the University of California Statewide Integrated Pest Management site.

Kleptoparasite

The tiny flies are feeding on the stink bug which is the lynx spider's prey. Thanks to the people at Bug Guide for the i.d. on these milichid flies. This family of flies has a diverse repertoire of lifestyles, as described here. These flies specialize in waiting for a certain predator to capture it's prey, then swooping in to suck nutrients off of the presumably still living unfortunate. Klepto- for thieving; parasite- for, well, parasite. The parasitism is on both the spider and the prey (which is not always stink bugs: I've seen these flies on other prey including honeybees). Not sure what the fly larvae feed upon . . . will research that further. The complexity of the bug world never stops amazing me.

Assassin bug all grown up

The assassin bug nymph from the 6/24 post is all grown up now, but still doing the same things. Here is an adult taken on 7/31, waiting for prey on a queen anne's lace flower. This is one of their favorite spots for catching flies, bees, or small butterflies. How long bugs spend in each of their life stages is important to know, along with their first emergence in the growing season. The nymph in my 6/24 post was well-developed, close to becoming adult. It has been 38 days since that photo was taken. What is the generation time for this species in mid-summer? How long do the adults live? Could this individual be the same one from 6/24, could it be a grand-daughter, or is it on a different life line altogether?

As summer progresses, it's common to see more life stages of an insect species present concurrently, until winter (the great equalizer) resets the starting line for the following spring. Here's another view of one of these adult assassin bugs, taken Aug 9. Maybe this is the same one, since it is on the same flower. This is 47 days since the first photo of the nymph. How far do they travel during their short lives? Is it likely one's entire existence would be spent on the same rudbeckia plant?

Mystery pest

This is insect damage on a privet (ligustrum japonicum) hedge. The chewed leaves are limited to the lower 5 to 6 feet of the planting, and are spotted here and there with this example being about the worst of it.

There was no obvious culprit the days I checked. I found some tiny (2mm) round brown and tan beetles just standing around on the underside of some leaves. I don't think it's likely they could eat this much. There was a lone grasshopper trying out the taste of privet, but not only is their chewing pattern different, but there aren't enough of them to be responsible for this much damage.


Can't be leaf cutting bees because the cutouts aren't clean and round enough; these bees make almost perfect circular cuts in rose and other leaves. I'm thinking it's a beetle doing this damage, which is similar to what the eucalyptus leaf beetle or australian tortoise beetle does to eucalyptus leaves. And I'm thinking it's nocturnal. Must get new batteries for flashlight.