Saturday, July 4, 2009

The Eyed Click Beetles of the United States and Canada (Coleoptera: Elateridae)

The eyed click beetle (Alaus oculatus) is probably the most well known click beetle in North America. It is a fairly large insect (usually longer than an inch) and quite attractive - even arresting. The large eye spots on the pronotum are enough to stop most anybody who might happen upon one of these insects. Of course the eye spots are not true eyes. Eyes, after all, don't occur on the pronota (or any of the thoracic segments) of insects. But it's hard not to think that the impressive insect is looking at you when you happen upon them in the woods.

What is less well known is that the eyed click beetle per se is just one of six related species of click beetles with similar eye spots that occur in the United States. Three of them (A. oculatus, A. myops, and A. melanops also occur in Canada). One of them occurs only at the tip of Florida (A. patricius). In fact it is very likely that if you come upon one of these attractive insects, you will be looking at one of the other five species. Following are a few pictures that I hope will help you figure out which species are which. For a full treatment of the species see Sonia Casari's excellent treatment of the genus Alaus (Systematics and Phylogenetic Analysis of Alaus Eschscholtz, 1829 (Coleoptera: Elateridae) in Revta. Bras. Ent. (1996) 40(2): 249-298).

By far the most common species in the Rocky mountains and west is A. melanops. The only exceptions
to this are in Arizona and New Mexico where two other species also occur. Alaus zunianus (occuring only in Arizona) and A. lusciosus (which occurs from Arizona east to Texas and north to Kansas). The best way to tell the difference between A. zunianus and A. melanops is the amount of white on the pronotum. In A. melanops, there is much less white. The eye spots are surrounded by black. In A. zunianus, the eye spots are adjacent to a lot of white. To separate A. zunianus from A. lusciosus it is best to look at the position of the eye spot relative to the middle of the pronotum. In A. zunianus, each eye spot is as close to the center as it is to the side. In a A. lusciosus each eye spot is closer to the side. Alaus melanops can also be separated from A. lusciosus by the width of the white lateral band on the pronotum. This band is wide and connects to the outer edge of the eye spots in A. lusciosus much like it is in A. zunianus.
If you find an eyed click beetle east of the Rocky mountains there are primarily three species you need to be able to tell apart. The easiest to recognize is A. myops which has much smaller eye spots than than the other species. In fact the eye spots of this species are often much more elongate than in either A. oculatus or A. lusciosus.

The ranges of both A. myops and A. oculatus overlap extensively (both occur in all states east of the Great Plaines and north into Canada). The range of A. lusciosus, on the other hand, only overlaps with these two species in Kansas, Oklahoma and Texas. Nonetheless, where there is overlap, A. lusciosus is commonly misidentified with its better known congener, A. oculatus. The best way to tell these two species apart is to look closely at the base of the elytra (that is the wing covers behind the pronotum where the eye spots are located). If the space between the elytral lines (called striae) are convex than the species is A. oculatus. If the space is nearly flat it is A. lusciosus. Hopefully you can see this is the picture details of both species.
The only other species in the United States is A. patricius which occurs in the south of Florida. It has even smaller eye spots than A. myops but the more important character is that the eye spots in A. patricius are not surrounded by a white band as they are in A. myops (and the other four species).

Of course, there are always individual beetles that don't always fit neatly into the expected patterns. If you have a specimen that you aren't sure of and you need an acurate identification, your best bet is to contact a click beetle taxonomist or maybe take a visit to your state's land grant university and talk with the insect curator on staff. Good luck.










5 comments:

beetlesinthebush said...

Hi Sam - excellent summary of these spectacular beetles. I have four of the six species in my collection (missing lusciosus and patricius).

Unknown said...

We just found one of these on a tree outside today. He's in a jar right now so we could look at him, but he's missing a leg. Thanks for the info, I plan on letting him go after the storm is over. He's definitely the first one, after comparing the pictures. I've never seen one before, even though I've lived in Delaware for years.

Crooked Beak said...

Hey Sam, very well done and informative post on a group of interesting and spectacular beetles. My interests were recently piqued when I found a zunianus in one of my fermenting bait traps in SE AZ.

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