four-lined hornet fly

(Spilomyia sayi)

               
Conservation Status

IUCN Red List

not listed

four-lined hornet fly

NatureServe

NNR - Unranked

Minnesota

not listed

Occurrence

Fairly common

Flight/Season

Early July to mid-October

Habitat

Wetlands in deciduous forests, sometimes on hilltops

Size

Total Length: 716 to (10.4 to 16.6 mm)

         
         
         
          Photo by Alfredo Colon
 
Identification

Four-lined hornet fly is a medium-sized, wasp-mimicking, flower fly. It occurs in northern United States from Maine to Minnesota, and in southern Canada from New Brunswick to Saskatchewan. In Minnesota, where it is at the western extent of its range, it has been recorded in the northeast, north-central, and metro regions. Adults are found from early July to mid-October hovering around flowers in wetlands, sometimes on hilltops. Larvae are found in deep rotholes in trees. A rothole is a cavity formed at the site of a wound as the result of fungal and bacterial action. A deep rothole is a rothole that does not heal. The water inside is mostly from the vascular system of the tree, not from rain, and is reddish-brown, not clear.

Four-lined hornet fly mimics vespid wasps (Family Vespidae) in both appearance and behavior, but unlike wasps it cannot sting. The face is yellow and straight, not concave. The lateral parts of the head (gena), equivalent to the cheeks, are yellow. A black line separates the face and gena. The antennae are are black and have three segments. They are longer than most members of this genus. The basal segment (scape) is long, at least 1.5 times as long as the second segment. The second segment (basoflagellomere) is elongated, much longer than wide. The third segment is longest and has a large, brownish-yellow bristle (arista) on the upper side. The structure of protruding mouthparts (proboscis) is short and fleshy. There are two large compound eyes on the sides of the head and three small simple eyes (ocelli) in a triangle on the top of the head. The compound eyes are dark brown with an obvious yellow pigmented pattern that helps to disguise the large eyes. On the male the compound eyes meet at the top of the head. On the female they do not meet, and the black lines between the face and gena taper and converge approaching the ocelli, becoming a single thin brown line at the front ocellus.

The thorax is black with yellow markings. The large exoskeletal plate (scutum) covering the middle segment of the thorax has two pairs of yellow spots on the front margin, a yellow line on each side from the rear margin that bends inward at the transverse suture, and a pair of oblique yellow lines at the rear margin that form an inverted V. The small plate covering the upper rear portion of the thorax (scutellum) is entirely black.

The abdomen has four segments, and each segment is covered by a hardened exoskeletal plate (tergite). Tergite 1 is entirely black. Tergites 2 and 3 are black with a single yellow band. The band on tergite 2 is complete but may be shallowly notched in the middle. The band on tergite 3 is deeply notched or slightly separated in the middle. There are two bands on tergite 4. The front band is noticeably separated in the middle.

The wings are mostly clear but the front third is darkened. The small, knob-like structures on each side of the thorax (halteres) used for balancing in flight are yellow. There is a spurious vein between the radius (R) and media (M) veins. The cross-vein that runs between the R and M veins is strongly oblique. The anal cell is long and is closed near the wing margin. The R5 and M2 cells are also closed. The radial sector vein (Rs) has 2 branches.

The legs are mostly yellow. The third segment (femur) of the hind leg is at least half black and has an unbranched spur near but not at the tip. The fourth segment (tibia) of the front leg is mostly black, yellow just at the base. The last part of the leg, corresponding to the foot, has 5 segments. It is black on the front legs, yellow or brownish-yellow on the middle and hind legs.

 
Similar
Species

 

 
Larval Food

 

 
Adult Food

Pollen and nectar of goldenrods, flat-topped aster, pearly everlasting, and other plants whose flowers produce large amounts of pollen.

 
Life Cycle

 

 
Behavior

 

 
Distribution Distribution Map  

Sources: 24, 29, 30, 82, 83.

 

 
Comments

 

 
Taxonomy

Order:

Diptera (gnats, mosquitoes, true flies)

 

Suborder:

Brachycera (circular-seamed flies, mouches muscoïdes, muscoid flies, short-horned flies)

 

Infraorder:

Muscomorpha

  no rank:

Eremoneura

  no rank:

Cyclorrhapha (circular-seamed flies)

 

Section:

Aschiza

 

Superfamily:

Syrphoidea

 

Family:

Syrphidae (hover flies)

 

Subfamily:

Eristalinae

 

Tribe:

Milesiini

 

Subtribe:

Milesiina

 

Genus:

Spilomyia

 
Synonyms

Paragus quadrifasciatus

Paragus sayi

Spilomyia quadrifasciata

 
Common
Names

four-lined hornet fly

 

 

 

 

 

 

Glossary

Arista

A large bristle on the upper side of the third segment of the antenna of a fly.

 

Femur

On insects and arachnids, the third, largest, most robust segment of the leg, coming immediately before the tibia. On humans, the thigh bone.

 

Gena

In insects, the area below the compound eye. In birds, the feathered side (outside) of the under mandible; the area between the the angle of the jaw and the bill.

 

Halteres

In flies: a pair of knob-like structures on the thorax representing hind wings that are used for balance.

 

Ocellus

Simple eye; an eye with a single lens. Plural: ocelli.

 

Proboscis

The protruding mouthpart(s) of a sucking insect.

 

Scape

On plants: An erect, leafless stalk growing from the rootstock and supporting a flower or a flower cluster. On insects: The basal segment of the antenna.

 

Scutellum

The exoskeletal plate covering the rearward (posterior) part of the middle segment of the thorax in some insects. In Coleoptera, Hemiptera, and Homoptera, the dorsal, often triangular plate behind the pronotum and between the bases of the front wings. In Diptera, the exoskeletal plate between the abdomen and the thorax.

 

Scutum

The exoskeletal plate covering the forward (anterior) part of the middle segment of the thorax in some insects.

 

Tarsus

On insects, the last two to five subdivisions of the leg, attached to the tibia; the foot. On spiders, the last segment of the leg. Plural: tarsi.

 

Tergum; tergite

The upper (dorsal), hardened plate on a segment of the thorax or abdomen of an arthropod. Plural: terga.

 

Tibia

The fourth segment of an insect leg, after the femur and before the tarsus (foot). The fifth segment of a spider leg or palp.

 

 

 

 

 

       
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Alfredo Colon
       

Outstanding eyes

  four-lined hornet fly   four-lined hornet fly
       
  four-lined hornet fly   four-lined hornet fly
       
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Other Videos
 
  Diptera: Syrphidae (Hover flies): Spilomyia sayi wing waving
Stuart Tingley
 
   
 
About

Aug 4, 2013

This spectacular wasp-mimicking hover fly, Spilomyia sayi, almost constantly waves its' wings as it nectars on goldenrod at Jolicure, Westmorland County, New Brunswick, Canada on 4 August 2013.

   
       
  Spilomyia sayi (four-lined hornet fly), 10/19/19.
She Who Tends the Woods
 
   
 
About

Oct 20, 2019

Neat little wasp mimicking syrphid fly warming itself in our garden. I do eventually zoom in for a closer look. :)

   
       

 

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Alfredo Colon
8/29/2019

Location: Woodbury, Minnesota

outstanding eyes

four-lined hornet fly


     
     
 
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Created: 5/5/2020

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