Scuttle Flies

Have you ever noticed how there are these little tiny flies that run, stop, and run in a seemingly random fashion around your kitchen or bathroom? Sorry, I sound like Andy Rooney. Well, they are not schizophrenic “fruit flies,” but a different kind of fly altogether. Scuttle flies belong to the family Phoridae, and are also known as humpbacked flies or coffin flies.

The most common species of phorid by far, at least in the urban environment, is Megaselia scalaris. Males are roughly two millimeters long, females about three, so if they didn’t move you might not even notice them. They are also very easily confused with vinegar flies (aka pomace flies) in the family Drosophilidae, which we call “fruit flies.” I’ll point out the differences shortly.

I habitually find Megaselia scalaris around the garbage disposal in the kitchen sink. This should not be surprising. The larval flies feed in a variety of decaying organic matter. These little maggots might drown in the drain trap, but they can swallow air to make themselves buoyant and avoid that fate.

Dr. Brian V. Brown, an entomology curator at the Natural History Museum of Los Angeles County, is one of the leading authorities on the family Phoridae. While 90% of the specimens he is asked to identify turn out to be Megaselia scalaris, there is an enormous number of undescribed species, even within the genus Megaselia, which accounts for about half the species in the family.

It is important to note that even the cleanest homes and businesses are bound to have scuttle flies at some point, and they rarely reach population levels that make them any more than a nuisance. They present no health threat to the average person, but they have been recorded as infesting wounds in hospital patients. This phenomenon is known as “myiasis,” and is exceedingly rare. Check out This abstract if you want the gory details of an example from overseas.

The vinegar flies in the Drosophilidae family are probably a little more common than phorids in the average house, but with a little practice you can easily tell the two apart. Above is an image of a Drosophila. Note the large head in proportion to the body, with bright red eyes. Scuttle flies, like the magnified specimen shown below, have smaller heads with dark eyes. The “thighs” on the hind legs are heavier than those of vinegar flies, too.

Still, behavior is the biggest clue. Scuttle flies run in a darting fashion, only flying if dodging you on foot doesn’t work. Vinegar flies perch, and while they may walk slowly, never seem to run. Their instinct is to fly to avoid a potential threat.

Sources: You will find this link from Bugguide.net to be helpful in learning more about these common yet fascinating flies. The chapter on Phoridae in the Manual of Nearctic Diptera is in volume 2, now available as a free PDF download. The Manual is the reference to North American flies, even though it is already somewhat out of date.

Wasp Wednesday: Euodynerus hidalgo

Caterpillars have it hard in life. Everything is out to get them, especially wasps. Ichneumon and braconid wasps lay eggs on them. Chalcid wasps lay eggs in them, and predatory wasps in the families Vespidae and Sphecidae sting them. Among the vespid wasps are mason wasps, of which Euodynerus hidalgo is typical.

This species ranges across the United States from the Atlantic to Pacific coasts, and is divided into three subspecies. Nancy Collins was kind enough to help me find the above example of E. hidalgo hidalgo in Mission, Texas on June 6, 2010 at the visitor center for Bentsen Rio Grande Valley State Park.

The female wasp was plastering mud in the mortar crevice between bricks on the exterior wall of the building. They normally nest in pre-existing cavities including the abandoned nests of other wasps, or old solitary bee burrows. So, old nests of Black and Yellow Mud Daubers (Sceliphron caementarium), and even the nests of paper wasps (Polistes) are fair game for homesteading.

More life history information is known for the subspecies E. hidalgo boreoorientalis, which occurs along the Eastern Seaboard. I found a couple specimens in Cape May Point State Park, New Jersey on October 18, 2010. Note that this subspecies has almost no red markings, being mostly black with sparse yellow markings. Thanks to the dedicated work of Karl Krombein, we know this subspecies nests mostly in old bee or beetle borings in twigs and stalks.

According to Krombein’s observations, nests may consist of one to eleven cells, arranged linearly along the length of the tunnel. Each cell is furnished with several small caterpillars, paralyzed by the sting of the female wasp. An egg is laid in the cell, then a partition of sand or soil is fabricated and a new cell is created atop the previous cell. The egg and larval stages were completed in about 7-9 days at the Kill Devil Hills site in North Carolina where Krombein did most of his research. Adult male wasps emerged from the pupae in about 14 days, whereas females emerged after 19 days. Krombein suspects that at least two generations are produced each year.

Many members of the genus Euodynerus have a blocky or “chunky” appearance, especially the thorax with its angular edges. E. hidalgo is identified by the strong carina (ridge) on the front edge of the pronotum (collar-like part of the thorax abutting the head), and the thin, slightly upturned hind margins of the second and third dorsal abdominal segments. Male specimens are easily recognized by the hooked tips on the antennae.

Like most mason and potter wasps in the subfamily Eumeninae, this species is frequently seen on wildflowers feeding on nectar. Look for these and other wasps nesting in or on old barns and other dilapidated wood buildings. Some wasps will build mud or paper nests, while others will use the holes where rusted nails have fallen out.

Sources: Karl V. Krombein’s masterpiece, Trap-Nesting Wasps and Bees: Life Histories, Nests and Associates, published in 1967 by the Smithsonian Press, is a 570 page bible for anyone interested in solitary wasps and bees. Online, you may find this ”Identification Atlas of the Vespidae of the northeastern Nearctic Region” to be helpful. It is well-illustrated, a product of the Canadian Journal of Arthropod Identification.

Wasp Wednesday: Great Golden Digger

Few insects are so conspicuous and arresting as to be granted a common (English) name, but the Great Golden Digger wasp, Sphex ichneumoneus is one of them. This large, colorful solitary wasp is so regal that one can’t help but notice and admire it.

Sphex ichneumoneus is a common wasp with a transcontinental distribution in North America. I have personally seen this species in Oregon, Ohio, and Massachusetts, but it ranges all the way to Peru and Brazil. At 15-27 millimeters long, they are not easy to ignore, either. Most of the time one sees them on flowers foraging for nectar.

Females are fossorial (diggers) that excavate burrows in the soil. In contrast to sand wasps which actively kick out sand behind them as they go, Sphex wasps gather loads of soil in their front legs, under their “chin,” and back out of the hole, depositing the load a short distance from the nest. Richard Walton has a fantastic online video of this species that chronicles the nesting behavior of a typical individual female.

The female wasp hunts katydids as food for her offspring, paralyzing the large longhorned grasshoppers with her sting and flying or lugging their limp bodies back to her nest. This must take a Herculean effort, but the wasp appears nonchalant, though determined. She drops her prey at the doorstep, enters her nest to inspect it, then retrieves her prey and drags it head first into the burrow. This pat sequence of behaviors has stimulated researchers to test the wasp’s patience. At least two observers have teased a wasp by repeatedly moving her prey away from the doorstep, causing her to move it back to the edge, inspect the nest again, then come back for the prey, over and over. So persistent are these wasps that every subject outlasted its human tormenter!

Host katydids victimized by Great Golden Diggers include the formidable coneheads in the genus Neoconocephalus, and slightly more helpless species in the genera Orchelimum, Conocephalus, Scudderia, Amblycorypha, Neduba, and Atlanticus. Tree crickets (Oecanthus) and leafroller crickets (Gryllacrididae) have also been recorded as prey.

A typical nest burrow is vertical or nearly so, terminating in two to seven individual cells. Several prey insects are stored in each cell, though it takes fewer of the larger katydids to provide for a single larval wasp.

Even though this species is solitary, several females may dig their nests in the same general vicinity, giving the appearance of a “colony.” Find one and you may find others nearby.

Watch for males perching on flowers, foliage, and other high points, themselves watching for females. The golden pubescence and bi-colored abdomen of this species make it impossible to mistake for any other wasp of that size, including other species of Sphex.

Merchant Grain Beetle

Even entomologists are not immune to pest insects in their homes. We are just a little more fascinated than we are revolted. So, when I found a tiny beetle crawling on the bathroom counter of my Tucson apartment on October 20, 2010, I naturally wanted to know more about it. I thought I had a good idea of its identity, but I was wrong about the species.

Among the more common “stored product pests” found in the average household are silvanid bark beetles in the family Silvanidae. I know! What would a bark beetle be doing in the pantry? Well, while most species live under bark on trees, logs and stumps, other species are pests of stored grains. They are tiny, prolific, and hitchhiking on commerce to all corners of the globe.

The specimens in the images here are about three millimeters long. I thought they were the species Oryzaephilus surinamensis, the “Sawtooth Grain Beetle.” The common name comes from the tooth-like projections on the insect’s pronotum (top part of the thorax). It turns out there is a nearly identical species, the “Merchant Grain Beetle,” Oryzaephilus mercator, and if I am correct, that is what my specimens are. The Merchant Grain Beetle has slightly larger eyes than its counterpart, such that there is scarcely a “cheek” behind each eye. The Sawtooth Grain Beetle has much more prominent cheeks.

Adults and larvae of the Merchant Grain Beetle occur mostly in cereal grains like oatmeal, rolled oats, and bran, and also brown rice. Great, they get more fiber than I do. Oilseed products like nuts and shelled sunflower seeds are also prone to infestations. At optimal temperatures and humidity, these insects can go from egg to adult in three to four weeks.

Adult Merchant Grain Beetles can live a surprisingly long time. Their average lifespan is six to ten months, but they are known to live as long as three years. They are strong fliers, too, which allows them to wing their way to new food sources and locations instead of relying on human transport to exotic new locales (the Sawtooth Grain Beetle is flightless). Females of both species deposit between forty and 285 eggs in their lifetime.

I still don’t know where my beetles are coming from (I found a second one on December 20), and I’m kind of afraid to look. Thankfully, they don’t pose any outright threat to human health. I suppose you won’t want to come over for breakfast now, though….

Sources: A great resource for images of stored product pests in general is the website of the Stored Product Insect Research Unit of the United States Department of Agriculture’s Agricultural Research Service. The entomology departments of many universities produce very helpful online fact sheets about various insects through the Cooperative Extension Service. I found this one from Penn State in my research for this blog entry.