The Maggot on the Rosebush: Aphid-eating Flower Fly Larvae

Gardeners cannot always be faulted for not understanding who their insect friends are. Entomologists have done a relatively poor job of advising the public on what garden insects are pests, and which are beneficial. It is especially problematic when you consider metamorphosis. You do not always know which larva corresponds to which adult, and whether both life stages are helpful or harmful. Case in point, larvae of flower flies (family Syrphidae), also known as "hover flies."

The overwhelming majority of flower flies in the subfamily Syrphinae are aphid predators in their larval stages. What you might easily mistake for just another flower- or foliage-munching caterpillar on your rosebush is probably one of these allies in your war on pests.

Killing an aphid!

Not that you would even notice them, as they can be incredibly cryptic, disguised as a discolored patch on the edge of a leaf, or a shed pollen cone on a pine tree....

Flower fly larva on pine needle

Female syrphid flies lay eggs in or near aphid colonies. The tiny larvae that hatch feed and grow, with three instars before pupation. An instar is the interval between molts. Despite its elastic appearance, the larva still has an exoskeleton that must be shed in order for the insect to grow larger. The final molt results in the pupa stage, a convex pear-shaped lump attached to a leaf, stem, or other substrate. The adult fly eventually emerges from the capsule-like pupa.

A little Allograpta sp. flower fly

Most adult syrphids strongly resemble wasps or bees, to the degree that they frequently fool entomologists. Like their hymenopteran models, the flies are capable pollinators of various flowers, visiting blossoms for nectar and picking up pollen in the process.

Adult female Syrphus sp. laying eggs in aphid colony

Flower flies can be recognized by their hovering behavior (few bees are capable of hovering, oddly enough), enormous eyes that meet at the top of the head in males, and nearly meet in females, and only one pair of wings to a bee's two pairs. Flower flies also have very short antennae in most cases, whereas bees and wasps have longer, thicker antennae, often "elbowed" where the first, long segment is connected to the remaining shorter segments.

A tiny Toxomerus sp. pollinating a flower

Lastly, while bees and wasps have chewing mandibles and sometimes a tongue-like arrangement of other mouthparts, flower flies have an extendable...."arm" tipped with a sponge-like pad. This organ is retracted under the fly's "chin" when not in use.

Adult Eupeodes or Syrphus sp.

Syrphid flies are among the most abundant of garden insects, especially conspicuous in spring and fall when aphid populations are at their peak. Watch for them and be careful not to accidentally kill their larvae when you are contemplating taking aphid control into your own hands. Between syrphid larvae, lady beetle larvae, and lacewing larvae, you may not have to do anything to keep aphids from reaching destructive numbers.

Another one bites the dust!

Sources: There are several excellent online resources about syrphids.
Rotheray, Graham E. 1993. "Colour Guide to Hoverfly Larvae in Britain and Europe," Dipterists Digest. No. 9. Sheffield, England: Derek Whitely and the Royal Museum of Scotland. 160 pp.
Flower Fly Survey of Los Angeles County
University of California Integrated Pest Management website on syrphids.
Texas A & M University website

The Myth of "Good Bugs" and "Bad Bugs"

Almost every insect identification request I receive includes the same question: "Is this a good bug or a bad bug?" Ok, another frequent question is "How do I get rid of it (them)?" The concept that any particular species of any organism is inherently good or bad is a symptom of collective ignorance, and I am not sure that the entomological community has done much to counteract that logic.

Caterpillars of the Cloudless Sulphur eat Senna. Can you live with that?

A good deal of our opinions and beliefs have been biased by large scale agriculture, and the fear-mongering media coverage of economic pests. You also have "organic" advocates who promote "beneficial" species, which they often have for sale in their nurseries and other businesses. The common denominator in those instances is money. Millions, if not billions, of dollars are at stake in products ranging from household and garden pesticides to bug zappers to laboratory-reared lacewings and parasitic wasps. Don't you know that you can't live without any of this stuff?

Get behind the sales pitch and the reality is much more subtle and variable. Take the praying mantis, for example. Here in the U.S. you can purchase the egg cases (ootheca) of the European Mantis, Mantis religiosa, for your garden, despite the fact that in most areas of the country you already have one if not several native species already there.

A native mantis eats a Queen butterfly

Then there is the idea that mantids are beneficial predators. Mantids are completely indiscriminate hunters. They will eat bees and butterflies as often as grasshoppers and caterpillars. There are even well-documented incidents of larger species killing hummingbirds. Mantids still looking wonderful to you now?

Phytophagous (plant-eating) insects, on the other hand, simply must be pests, right? If so, then how come so many species have been imported from overseas to control noxious weeds? Most herbivorous insects are highly "host specific," meaning they feed on only a few, closely-related plants. Those plants have learned to co-exist with the insects that eat them. The plants produce their own chemical defenses, and even "talk" to other nearby plants to warn them of an impending infestation. Native plants are better able to withstand an onslaught because they are growing in suitable soil and climate. This also allows them to quickly recover from even the most intense defoliation.

This leaf beetle was imported to control saltcedar (Tamarix spp.)

You can also not equate your garden, yard, or woodlot to a massive farm, orchard, or forest. The reason there are pests at all is because we insist on growing large scale monocultures of various crops (and I would include tree farms in that). What self-respecting European Corn Borer is going to turn up its nose (antennae?) at acres and acres of its host plant? We set the table and then complain about our uninvited guests.

The real world of nature does not play favorites, and if you want a healthy planet Earth, let alone a garden, yard, or home, then you have to stop thinking of every species as "good" or "bad." You don't have to like every creature. Personally, I don't like mantids, but I do recognize their place in the grand scheme of things, and appreciate their existence for that reason alone.

I heartily encourage a public attitude that embraces all life forms, treats them with respect, and actively cultivates a sustainable human culture in which we can all coexist....SLAP! Sorry, there was this mosquito....

Little Bugs with a Big Bite: Minute Pirate Bugs

Sometimes it seems the tiniest of insects is the biggest nuisance. Mosquitoes come to mind, as well as black flies, and "no-see-ums" or "punkies" (biting midges in the family Ceratopogonidae). One other insect often responsible for surprisingly painful bites is the aptly-named "minute pirate bug." There are about 90 species in the family Anthocoridae found in North America, in 22 genera, but only a few cause us grief.

Insidious Flower Bug biting me in Colorado

The Insidious Flower Bug, Orius insidiosus is, appropriately, the species most likely to get under your skin. Well, on your arm, hand, or neck, where it will likely probe you painfully. At only 2-2.5 millimeters, it is possible to overlook it entirely when trying to pinpoint the source of your irritation. In the right light, however, the little bug appears bright white and black.

Despite dispensing unprovoked bites, Orius insidiosus is actually a highly beneficial bug. It is a predator of many crop pests like very young caterpillars of the corn earworm, plus insect eggs, aphids, whiteflies, thrips, and mites. Consequently, this minute pirate bug is reared commercially and sold to farmers as a biocontrol agent.

It takes only twenty days, on average, for O. insidiosus to go from egg to adult. Females lay two eggs per day, and about thirty during their lifetime. Each ovum is deposited in foliage such that the top of the capsule protrudes above the leaf surface. In about four or five days, the first instar nymph emerges from the egg. During the next two or three weeks, the nymph goes through a total of four more instars before transforming into a fully-winged adult bug. The adults live an additional three or four weeks.

Insidious Flower Bug biting me in Kansas

Adult Insidious Flower Bugs overwinter in leaf litter and probably other debris on the ground. Several generations can be produced annually over the insect's wide geographic range. It occurs east of the Rocky Mountains, plus parts of California, and has been introduced to British Columbia. Because it is available commercially, it has likely spread elsewhere, too.

Adult Anthocoris musculus, Colorado

Another species I have found commonly here in Colorado Springs is Anthocoris musculus. It is a real giant by pirate bug standards, measuring 3.4-4.0 millimeters as an adult. I have found it associated with cottonwood trees, and it is well-known from willows and other deciduous trees and shrubs as well as herbaceous plants.

Nymph of Anthocoris musculus, Colorado

It is potentially an important predator in orchards, and has been observed eating red mites and "eye spotted bud moth" in Nova Scotia (Kelton, 1978). This species ranges throughout most of North America including Alaska and northern Canada.

The next time the pirate bug bites, simply utter "Ar-r-r-r!" and remember their beneficial qualities. After all, they are probably keeping your garden free of other tiny pests.

Adult A. musculus feeding on unknown object, Colorado

Sources: "Minute Pirate Bug aka. Orious insidiosus," Evergreen Growers Supply.
Gibb, Tim. 2006. "Have a thick skin when it comes to Insidious Flower Bugs," Purdue Plant & Pest Diagnostic Laboratory, Purdue University Extension
Hull, L.A. and R.L. Horsburgh. "Minute Pirate Bug, Orius insidiosus (Say)," Mid-Atlantic Orchard Monitoring Guide.
Kelton, Leonard K. 1978. The Anthocoridae of Canada and Alaska. Ottawa: Canada Department of Agriculture. Publication 1639. 106 pp. (PDF).
Slater, J.A. and R.M. Baranowski. 1978. How to Know the True Bugs. Dubuque, Iowa: Wm. C. Brown Company Publishers. 256 pp.

Wasp Wednesday: Blue-winged Wasp

One of the most common solitary wasps of late summer and fall is a member of the family Scoliidae known as the “Blue-winged Wasp,” Scolia dubia. This is a fairly large insect, 20-25 millimeters in length, and easily identified by its bi-colored abdomen: Black on the upper half and red on the bottom half, with two bright yellow spots in the red area. There is rarely any variation in that color scheme, either. The common name stems from the brilliant blue highlights in the black wings that shine when sunlight hits them just right.

Scolia dubia is also a widespread species, found from Massachusetts to Florida, and west to Colorado, Arizona, and southern California. I have found them in New Jersey, Ohio, and Colorado. They are parasites of the grubs of scarab beetles, particularly the Green June Beetle, Cotinis nitida, and Japanese Beetles, Popilla japonica. Since Colorado has neither of these species, the Blue-winged Wasp must exploit a different host here. We certainly have plenty of May beetles (genus Phyllophaga), and the Bumble Flower Beetle (Euphoria inda), so I suspect those are the local hosts here in Colorado Springs.

The female wasp somehow divines the presence of beetle grubs underground while flying low over the surface of the soil in what approximates a figure-eight pattern. When she detects one, she lands, and sets about unearthing it. Scoliid wasps have strong legs that are heavily spined. This adaptation facilitates their digging activities.

An exposed scarab grub will writhe around and seek to rebury itself immediately. The wasp stings the larva to paralyze it and allow her to manipulate it. She may leave the grub in situ, or tunnel below it, excavating a small chamber where she deposits the beetle larva and lays an egg on it, perpendicular its body. She then seals the chamber and leaves to start the process all over again, often staying underground and digging her way to the next grub.

Interestingly, these wasps may sting several grubs without laying eggs on them. The paralysis of the beetle larva is usually permanent, so regardless of whether they become food for larval wasps, the beetle grubs are unable to complete their own life cycle. This is a good thing if you happen to have an infestation of “white grubs” in your lawn or garden.

Back to the egg on the beetle grub, though. The wasp larva that hatches feeds as an external parasite on the grub for one or two weeks before spinning a silken cocoon around itself. There it will remain as a pre-pupa for the winter, pupating the following summer and eventually emerging as an adult wasp.

Male and female scoliid wasps commonly visit flowers to feed on nectar (and perhaps pollen). I find them most often on White Sweet Clover, Melilotus alba, thoroughworts (genus Eupatorium), and goldenrod (Solidago spp.). Males can be identified by their long antennae and overall more slender appearance. Males have a distinctive, three-pronged “pseudostinger” that is part of their external genitalia. Males cannot sting, and females are loathe to sting unless physically molested.

Another interesting aspect of the males is their behavior. Males also fly near the ground in a sinuous pattern, hoping to detect virgin females emerging from the ground. This usually happens in the morning, and males abandon their searching by late afternoon. At that time, they may gather together to roost for the night on vegetation, as the image below depicts.

© Tim Moyer via Bugguide.net

Keep an eye out for the Blue-winged Wasp in your own yard. Remember they are beneficial, but beware that large numbers of them may indicate you have a serious problem with white grubs.

Sources: Grissell, Edward E. 2007. “Scoliid Wasps of Florida, Campsomeris, Scolia, and Trielis spp. (Insecta: Hymenoptera: Scoliidae),” Featured Creatures, document EENY-409, Entomology and Nematology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences (IFAS), University of Florida.
Rau, Phil and Nellie. 1918. Wasp Studies Afield. Princeton, NJ: Princeton University Press. 372 pp (Dover Edition).

Wasp Wednesday: Wasp/Not Wasp

Previously on “Wasp Wednesday” we featured keyhole wasps of the genus Trypoxylon. Like most stinging insects, these wasps are models for other harmless insects that escape predators by pretending to be something more dangerous than they are: a sheep in wolf’s clothing if you will. Meet Pseudodoros clavatus, a near perfect imposter of a keyhole wasp.

A biologist friend once cautioned me on jumping to conclusions about which insects serve as models for various mimics, but just look at this fly. The elongated abdomen even has pale markings to make it appear narrower than it actually is. At 7-12 millimeters long, it is also similar in size to many Trypoxylon wasps. Besides looking like the wasp, the fly even behaves like it. Male keyhole wasps often hover in front of vertical objects, and the fly hovers just as well, if not better than, the wasp.

Ok, so how do you tell them apart, anyway? Above is the wasp. Note that it has two pairs of wings (though connected to each other they are usually still discernible as separate). The antennae of the wasp are thick and relatively long. They eyes are large, but do not take up the entire head or face of the wasp. Now look at the fly below. It has only one pair of wings. The antennae are so short they are scarcely visible. The eyes cover most of the head of the fly, and are not notched on the inner margin like those of the wasp.

Pseudodoros clavatus is a member of the family Syrphidae, collectively known as “flower flies” (“hover flies” in Europe). They are frequent, abundant visitors to flowers of all kinds. While they may be insignificant pollinators, they play their part in perpetuating wildflowers. Their good deeds extend to the larval stage as well. The maggots of Pseudodoros are voracious predators of aphids.

Seeing one of these slug-like larvae on your rose bush might lead you to think that it is also eating the plant, but watch one closely and you will see it methodically slaying aphids, seizing the tiny sap-suckers and hoisting them off the stem. The fly larva then sucks the hapless pest dry and discards the empty husk of its exoskeleton.

Look for this species from coast to coast in the United States and southern Canada. It may be confused with the similar genera Baccha and Ocyptamus in some parts of its range, but Ocyptamus species have at least faint dark markings on the wings (if only a bold leading edge to the wing). Baccha is more difficult to distinguish, but at least one species has a distinctly banded abdomen. The image below is still a Pseudodoros.

Bee Flies

The title above is not a noun and a verb, but the common name for the family Bombyliidae. Bee flies get that name from their obvious resemblance to bees, but it is a diverse family and not all of them are covered in fuzzy hairs or iridescent scales. Their life histories are likewise variable, and for most species are unknown. At least 800 species occur in North America north of Mexico. More await naming and description by scientists.

Spring is a great season to see bee flies. Look for them in open areas on sunny days, or even sunny spots in wooded areas. Many species, like the “greater bee fly,” Bombylius major, shown above, hover so perfectly as to appear to be levitating. Male bee flies in particular exhibit this behavior, perhaps defending small territories or displaying for females. You might easily hear one of these flies before you see it.

Many bee flies have elongated mouthparts, causing some people to fear them as blood-suckers. The proboscis is for probing flowers for nectar, though, and the flies are totally harmless to people and pets. Bee flies are probably mostly “flower visitors” rather than pollinators.

The larval stages of bee flies are definitely not harmless to other insects, and this makes them beneficial allies in the war against pests. At least some members of the genus Geron, shown above on an aster in western Massachusetts, are parasites of the caterpillars and/or pupae of bagworm moths in the family Psychidae. Bombylius major, a widespread species illustrated near the top of this article, is somewhat less helpful. Its offspring are parasitic in the nests of solitary bees that nest in the soil. This and related species are known as “bombers” because the female will hover over the entrance to a bee’s burrow and lob eggs into it with a flick of her abdomen. The larvae that hatch then seek out the host bee’s larvae, becoming external parasites upon them.

Members of the genus Villa, like the unidentified specimen from Arizona pictured here, are villains only to caterpillars of butterflies and moths, again functioning as parasites in the flies’ larval stages.

Larvae of Hemipenthes are hyper-parasites. That is to say they are “parasites of parasites.” They live as parasites of the larvae of ichneumon wasps, tachinid flies and other insects that are themselves parasites of caterpillars of butterflies and moths. How bizarre is that? I photographed this Hemipenthes eumenes (below) a little over a week ago here in Arizona.

Try looking for bee flies yourself next time you are out and about. You might also surf the ‘net to get a feel for what they look like. Start by browsing the images BugGuide.net for a great overview of the North American fauna. See more stunning images from all over the world at this Flickr search. You’ll be amazed by the beauty of these delicate insects.