Friday, December 9, 2016

ID Tip: Seven-spotted or Nine-spotted Lady Beetle?

Today's identification tip involves separating two nearly identical lady beetles: the Seven-spotted Lady Beetle, Coccinella septempuncta, introduced from Europe, and the native Nine-spotted Lady Beetle, Coccinella novemnotata. There is widespread speculation that the exotic Seven-spotted ("C-7") has displaced the native Nine-spotted ("C-9"), and indeed the latter species has become noticeably scarce over most of its former range, especially in the eastern U.S., over the last 35 years or so. That is why it is critical to be able to identify C-9 and report sightings to the Lost Ladybug Project.

Typical specimen of Seven-spotted Lady Beetle ("C-7")

Physical Features

The most dependable, though subtle, difference between these two species is found on the front edge of the pronotum (top of thorax). In the Seven-spotted Lady Beetle, only the corners, or "lapels" if you will, are white. The remainder of the pronotum is black. In the Nine-spotted Lady Beetle, the entire pronotal "collar" is white, so the front edge of the pronotum is white, from corner to corner.

Specimen of the Nine-spotted Lady Beetle ("C-9")

Meanwhile, the wing cover (elytron) of the Nine-spotted Lady beetle does bear an extra black spot, located near the "shoulder." This spot can, however, be vague or even obsolete. The markings on the pronotum are much more consistent.

The Nine-spotted Lady Beetle is usually slightly smaller than the Seven-spotted, and is more often a creamy orange in contrast to the brighter orange, or red, of C-7. Both species are polished (shiny) in texture, and highly convex or nearly hemispherical in shape.

Heavier spots on this C-9
Behavior

There is little difference in behavior between these two species. Both are predators of aphids and can be found on plants hosting aphid colonies.

Another example of the Nine-spotted Lady Beetle
Habitat

Habitat is not a good way to distinguish these two lady beetles, either. Both occur in a variety of ecosystems, from vacant lots, yards, gardens, parks, and forest edges to orchards and agricultural fields.

Complicating Factors

A nearly spotless form of the Multicolored Asian Lady Beetle

There are a surprising number of nearly identical lady beetle species, and simply counting the spots is a very unreliable way of making an identification. There is extreme variability in many species, especially the abundant Multicolored Asian Lady Beetle, Harmonia axyridis, which is yet another non-native ladybug. Not only does the number of spots on the elytra vary, but so do the markings on the pronotum. This species needs to be ruled out before you try and conclude whether your specimen is a C-7 or C-9.

Transverse Lady Beetle

Here in the western U.S., we also have the Transverse Lady Beetle, Coccinella transversoguttata, which resembles C-7 except that the spots on the elytra near the pronotum are connected to form a horizontal black bar between the "shoulders." The Transverse Lady Beetle also appears to be suffering in the wake of C-7's arrival.

Quiz Photo: Which species is this one?

Please keep a lookout for the Nine-spotted Lady Beetle where you live and during your travels. The more eyes in the field, the better will be our understanding of the status of this species, which has been the state insect of New York since 1989. Thank you.

2 comments:

  1. Is there a relatively simple way to rule out Harmonia?

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    Replies
    1. Not completely reliably, but Harmonia hardly ever has the same spot pattern as C-7 or C-9.

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