Introduction
If you live in the southwestern US you may have been lucky enough to find a small pale-yellow ladybeetle no more than a few millimetres long. Little do you know that this innocent little beetle is part of one of the greatest minefields in Coccinellid history.When I grew up in England I encountered the 22-spotted ladybeetle (Psyllobora vigintiduomaculata), a petite ladybeetle obsessed with the colour yellow. Everything about this species was bright canary yellow, from its eggs, larvae, pupae and adults. This is one of the easiest species to identify in Europe. In America however this is a whole different story, as there is not 1 but 6 species of Psyllobora, all of which are very similar.
The 20-spotted ladybeetle Psyllobora vigintimaculata (or P. 20-maculata for short) and the kidney-marked fairy Psyllobora renifer are two fairy ladybeetles notorious for co-occurring, particularly in California. At one time it was thought that renifer was limited to dry deserts. While surveying one of my damp, urban neighbourhood adjacent to Ventura County, I found 20-maculata by sweeping plants of Indian strawberry. But not a moment later another I had amassed a series of other, slightly odd looking Psyllobora. This was P. renifer, in what was one of the least desert-like habitats imaginable in so Cal. Since then others have found P. renifer in other urban areas, and in some states as far north as Kansas.
In fairness, separating species only by location is rarely a good idea. Even though the deserts and urban areas of Los Angeles are widely separated, for an insect with wings, anything could happen. Although we don't know that Psyllobora migrate in any way, several other ladybeetles are dedicated travelers, which is proof that if they feel like it, they can go out of their way.
So as for ID of these species, let's begin with a variation scale:
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| Variation scale in Psyllobora 20-maculata and renifer. Click to enlarge. |
As you can see at either end of the scale, identification of typical individuals is very straightforward. Unfortunately ladybugs are notoriously variable, and although not common it is only a matter of time before someone bumps into a specimen that is a bit less typical, more like those in the center of this scale. So what do you do if you find a specimen that is near the middle? For a while, there was nothing we could do. The species were so poorly studied that many of these specimens were left as unidentifiable.
For a while, and even today, information on separating these two species is very sparse. While I was composing my field guide to American ladybeetles composing the pages on these two species was troublesome. I didn't want to give out wrong information, just in case it was unreliable. Nor did I want to ignore them. After all what field guide would it be if it didn't explain how to separate them?
That's when I sat down and dedicated my time to working the two species out. I analyzed photos, specimens (both from museums and those I have found myself), and old publications, before finally discovering the secrets. I have since learned that of all specimens, less than 5% are unidentifiable as either species. That's a massive leap from a time where identifying as many as half of specimens was a troublesome endeavour.
Note that this guide is intended for separation of the species in California. A note on other states is given at the bottom of the page. Without further ado, let's dive in.
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Identification Traits
1. Bicolouration
As you can see from the diagram above, there is a tendency for 20-maculata to show a specific bicoloured pattern. While most of the markings are brown, there are 6 spots in particular which are black. That's the basal pair of spots at the front-center of the elytra, and 2 spots on each side near the legs. On renifer however, the main marking pattern is uniform brown or black all over. On some renifer the front row of 4 markings are brownish and paler, so be aware of that. It is not "bicolouration" itself that is important, but what is and what isn't.
A small side note that if you super-light the wings of renifer, you'll see a brown and black pattern just like 20-maculata. The only time this happens is if the beetle raises its wings to take flight, and you then shine a bright flashlight through both sides. Very specific I know, so don't worry about it.
Exceptions: Occasionally you may find a renifer with 2 visible black spots at the front, while the remaining markings are brown. Never though have I seen renifer with 4 black spots, let alone the full 6.
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2. Tapered saddle
While both species share the same base pattern, there is one spot in particular on 20-maculata that is usually missing on renifer. This creates a tapered front corner to the name-sake kidney marking. This applies to the great majority of renifer and is one of the most readily recognizable features. A tapered saddle is diagnostic to renifer when present.
Exceptions: About 20% of renifer have a small spot here, but not enough to destroy the tapering. 5% or less however have a larger spot here. In these cases this spot is often smaller than the equivalent spot on 20-maculata, but at this stage the marking is no longer tapered. In 2% or less of specimens the spot is equivalent to 20-maculata, and then other ID traits need to be looked at instead.
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3. Apical spots
20-maculata has very strong apical marks at the end of the elytra. When the marking is doubled, so that it resembles a sideways 8, this is diagnostic to 20-maculata. On renifer this marking is always single, and generally pale, cloudy, or otherwise greatly fragmented or absent entirely.
An apical marking that is clearly defined, but small or medium in size, can occur on both species with relative frequency.
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| Diagnosis of apical spots. This ID trait cannot be applied to specimens in the intermediate range. Click to enlarge. |
Exceptions: As noted above.
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4. Anterior-discal spots
70% or more renifer have missing, reduced or absent anterior-discal spots, as indicated by the diagram above. When the spots are not clean and intact, or are very small in size, this is diagnostic to renifer. If the spots are intact and large in size, this ID trait cannot be consulted as both species can exhibit large, intact anterior-discal spots.
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5. Discal smudge
Only renifer shows these small obscure markings in the center. A decent portion of renifer do not show it, though, so its only useful when present.
Exceptions: As noted above.
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6. Elytral suture
If you look closely at renifer it often looks dusty near the elytral suture. On 20-maculata it is usually clean. This effect is caused by strong black punctures clustered around the suture on renifer.
Exceptions: I do not consider this to be reliable at this time although it seems fairly consistent.
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Conclusion
Although a bit complicated, I hope this has answered anyone's questions about these 2 surprisingly troublesome species in California. I have seen countless Psyllobora at time of writing, and so far I have seen a handful of specimens out of 1000s that have not been diagnosable by at least 3 identification traits discussed on this page.As for outside of California, the most reliable separation is the tapered saddle feature covered in point 2. But most 20-maculata outside of CA have a very clean spot pattern, which is completely unlike that seen on renifer.
That's it for now. Drop by again in future and see what new articles await....
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