Stilted legs and laced borders

I saw a couple of interesting insects on this morning’s walk with Beauregard. The first was an aggregation of stilt-legged flies (family Micropezidae) on the trunk of a standing dead white oak (Quercus alba). This particular species—Calobatina geometra—is one of several occurring in Missouri, none of which have a common name and most appearing to mimic parasitic wasps of the family Ichneumonidae. Whether this is purposeful or happenstance is not clear to me, but the resemblance is strong enough to suggest the former even if the reasons are not clear. An interesting feature of these flies, beyond their large size and greatly elongated “stilt-like” middle and hind legs, is the manner in which they wave their forelegs in front of them. The highly visible white band above the black feet suggests this may be a mechanism for calling attention to themselves—although again whether this is to communicate with others of the same species or deceive potential predators/competitors is unclear to me. Like most other flies, stilt-legged flies have very short antennae, so perhaps they have adopted this behavior to allow the forelegs to function as “auxiliary antennae.” There seems to be much more that is unknown about these insects than is known—here is a link to information about them by the Missouri Department of Conservation.

Calobatina geometra (family Micropezidae) congregating on trunk of standing dead Quercus alba (white oak) in dry-mesic upland deciduous forest.
Calobatina geometra—note the white “flags” near the tips of the forelegs.

Also making their appearance on the low vegetation along the roadway in my neighborhood (through dry-mesic upland deciduous forest) are moths of the family Geometridae—the one photographed this morning provisionally identified as Scopula limboundata (large lace-border moth). The long, thin, “inchworm-like” caterpillars of this species feed on a variety of shrubs and herbaceous plants throughout much of North America east of the Rocky Mountains.

Scopula limboundata (large lace-border moth) resting on low vegetation in dry-mesic upland deciduous forest.

©️ Ted C. MacRae 2022


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