A leading candidate for the Best Lady Beetle Name award is the Twice-stabbed Lady Beetle (Chilocorus stigma), a dramatic-looking black species with two red spots. The pattern is not unique, though, and many other black-with-two-red-spots are often misidentified and called “twice-stabbed” – perhaps at least partially because it’s more fun to say “I found a twice-stabbed lady beetle” than “I found a member of the Hyperaspis signata group that can only be identified by dissecting the male genitalia.” Here are some tips for distinguishing the Twice-stabbed Lady Beetle from its many imitators.*
First, the “real thing,” Chilocorus stigma:
Notice the flared edges, shield-like shape, and solid black pronotum (the part of the thorax visible above the wings). These features are shared by other members of subfamily Chilocorinae, and several western species are nearly identical to C. stigma and can only be told apart via dissection. Fortunately, the eastern Chilocorinae are externally distinctive. You can be sure it’s C. stigma if the spots are round, further forward than the middle of the body, and the underside is half red and half black.
The two subfamilies with the most similar species are Scymninae, especially genus Hyperaspis, and Coccinellinae. Here is a sample scymnine, the Signate Lady Beetle (Hyperaspis signata).
Notice the smooth oval shape, lack of a flared “rim,” and the white markings on the pronotum. No red-spotted black Chilocorus has white on the pronotum, and while some are more oval than others, all have a flared rim. Hyperaspis species are typically smaller, too, and the underside is brown or black. (Note that female Hyperaspis may not have white on the pronotum, but the shape and size are consistent in both sexes.)
A sample species from Coccinellinae is the melanic (dark) form of the Ashy-gray Lady Beetle (Olla v-nigrum):
This smooth oval species always has white markings on the pronotum in both sexes. Typically the red spots are more triangular or half-moon shaped than round; they may also be ragged with irregular edges. If you’re wondering how to tell this species from the Hyperaspis with white-marked pronota, it is almost always larger and the underside is yellow-orange.
That’s the brief rundown of the common red-spotted black lady beetles. I’ll post additional entries on telling the Chilocorus species from each other, and on other melanic forms of Coccinellinae, just as soon as I get around to illustrating them!
*It may be literally true that the other species are imitators – Chilocorinae are among the worst-tasting lady beetles, and the lookalikes may be using Batesian mimicry to fool predators into thinking they’re just as unappetizing.