Minnesota Flies

Long-tailed dance fly (Rhamphomyia longicauda) is a small, black, long-legged fly. It is commonly found from May to July in deciduous woods near water. The wings are long and black. The head is round with large bright orange or red eyes. On the female, the middle and hind legs have a fringe of long, black, bristly hairs.

Every evening around sunset, males and females collect in same-sex swarms. Females and fly up and down, the behavior that gives this family its common name “dance-flies”. Females cannot hunt for prey. They receive protein from males as gifts in exchange for copulation. They swallow air, filling and extending their abdomen outward, saucer-like, falsely signaling males that their eggs are nearing maturity. The long hairy legs wrap around the abdomen, making it appear even larger. Males are attracted to females that have largest swollen abdomens and hairiest legs. An individual will break off and join the other swarm to select a mate.

With 7,003 species in 530 genera worldwide, robber flies are one of the largest and most abundant families of insects alive today. Bee-like robber flies, as the common name for the genus suggests, resemble bees. There are 240 species of bee-like robber flies, 62 species in North America north of Mexico. Few of the species have been given a common name. Laphria sacrator is one of several species famous for being a bumble bee mimic, so “bumble bee mimic robber fly” will stand in for the common name.

Bumble bee mimic robber fly (Laphria sacrator) is a short, robust, medium-sized, bee-like robber fly. It is fairly common in northeastern and north-central United States, including Minnesota. It has a stout thorax and a short abdomen, both partially covered with long yellow hairs making it resemble a bumble bee. It is one of the hairiest of the bee-like robber flies. Adults are ⅝″ to 1″ long.

Many insects that form detachable galls on oak. All but two of these are cynipid wasps. The two exceptions are the oak gall midges Polystepha pilulae and Polystepha globosa.

Oak leaf gall midge (Polystepha pilulae) is a long-legged, 1 ⁄16″ to ⅛″ long, mosquito-like fly (midge). Adults are impossible to identify by appearance in the field. However, the species can easily be identified by the gall it produces. Galls appear always on the upper surface of northern pin oak, northern red oak, and possibly black oak leaves. They are hard, 1 ⁄16″ to 3 ⁄16″ in diameter, and irregular in shape. They are green when they first appear in the spring, soon turning red or magenta. As they age they become brown and crusty. They can be easily detached from the leaf surface.

Oak leaf gall midge (Polystepha globosa) forms similar spherical galls on the undersurface of the leaves of black oak and possibly other oaks in the red oak group.

There are about 6,000 species in 200 genera of hoverflies. They are often seen hovering at flowers, hence their common name. Few of them merit a unique common name. Our species, Helophilus fasciatus, though fairly common, is not one of these, so we will call it “hoverfly” followed by its scientific name.

This hoverfly is robust and medium-sized, ⅜″ to ⅝″ long. It can be seen from late March to early October. Like many hoverflies, it is somewhat bee-like in appearance.

The genus Helophilus is identified by the striped thorax, on the wing the marginal cell open and the pterostigma lacking a cross vein, and the absence of a spur on the femur of the hind leg. Our species is distinguished by relatively narrow abdominal stripes, the narrowed area at the top of the head of the male, the all black hairs at the top of the face of the female, the space between the eyes narrower than the width of the pair of swellings at the base of the antennae, and the amount of black markings on the legs.

An abnormal growth (gall) on the stems, leaves, or buds of a plant can be formed by many insects, mites, and fungi. Willows are hosts to many parasitic insects, several of which form galls. Only willow pinecone gall midge (Rabdophaga strobiloides) forms a pinecone-shaped gall at the tip of a willow stem.

The adult midge is a small fly about 3 ⁄16″ long. It is most often identified by the large distinctive gall that houses the growing larva. The gall appears at the end of a willow stem. It consists of numerous, stunted, overlapping, loosely appressed, scale-like leaves. In the summer it is green, more or less globular, and densely covered with long, white, matted and tangled, woolly hairs. In the fall the cone turns brown and the shape resembles a pine cone.

bumble bee mimic robber fly (Laphria posticata)

heleomyzid fly (Suillia quinquepunctata)

red-tailed flesh fly (Sarcophaga haemorrhoidalis)

bare-eyed mimic (Mallota bautias)

hoverfly (Helophilus sp.)

common green bottle fly (Lucilia sericata)

horse fly (Tabanus spp.)