Hoplia Beetles on Western Azalea

One of California's truly spectacular flowers is the western azalea. Every time I see this plant in bloom - with its large showy white flowers - I have to remind myself that this is not an escaped houseplant.

I came across a couple of these very beautiful bushes this last week near Big Creek (a few miles north of Pine Flat Reservoir) in Fresno County. On one of the plants I discovered dozens of Hoplia beetles. These are scarabs with only a single claw on each foot (tarsus) that are ideal for hanging onto plants.
Fortunately for the azaleas, the beetles liked to aggregate around only a few flowers while feeding. I wonder if they taste as good as they look?

Odonteus obesus

Odonteus obesus is one of the two species of geotrupid scarabs most likely to be found in the Sierra Nevada (of California). It is about a centimeter long, is nearly black, and sports (in males) a prominent horn on its head. This individual is a female with little cephalic armature.

It came to a light last June at an elevation of about 5,000 feet near Shaver Lake (Dinkey Creek Campground) above Fresno. These compact scarabs are always fun to find.

The habitat was mixed Jeffrey pine, incense cedar and Douglas fir.

Pleocoma tularensis

Well it finally happened. After three years of searching, I finally found a rain beetle. I’m guessing that it is Pleocoma tularensis, but with the superficial (shall we say “stormy”) nature of rain beetle taxonomy, it might end up being P. fimbriata. In A.C. Davis’s revision, the two species are very difficult to distinguish. Linsley’s key to species resorts to geography to tell them apart. To complicate things, I found this individual in Fresno County fairly close to the point where the distributions of the two species meet. When this group is better understood, I expect that P. tularensis will be a subspecies of P. fimbriata (as Davis originally proposed). For those of you new to rain beetles, they are fairly large scarab-like beetles (family Pleocomidae at the moment). This one is well over an inch (30 mm) long.

Rain has come quite late this season. We normally have a good storm in November (maybe earlier). And it is this first storm that brings out the beetles (at least in many of the species). The first storm this season came this last weekend (in the middle of January). It starting on Friday afternoon and so I hurried home from work the same day, grabbed a bite to eat and drove up to Bretz Mill Campground about an hour above Fresno. I chose the place because the area combines grassy areas with mixed forest and riparian habitats. And it is also between 3,000 and 4,000 feet – a good elevation for rain beetles.

I put up two lights in the rain and waited a couple of hours without success. Maybe I should have left the lights on longer. Not wanting the rain to ruin my lights, I put them away and crawled into the back of the truck to sleep. By 6:00 the next morning I was wide awake and decided to drive home. Fortunately, I passed by a small community along the way with lights on and stopped to see what I might find. I found this individual crawling along the ground below one of the lights. (Both pictures are staged.) It was 6:40 AM, not much above freezing, with small patches of snow about, and with not another insect in sight. What a great way to catch beetles – and such an impressive one at that.

Polyphylla decemlineata

The ten-lined june beetle (Polyphylla decemlineata) is one of the most attractive pests in the Western US. It emerges towards the end of June / early July here in Fresno at which time it begins showing up at porch lights.

It's the unseen larvae (feeding as grubs on roots) that cause the damage, and they are known to feed on a variety of plants. In a suburban neighborhood (were I live) it isn't really possible to know who's yard they are coming from and so controlling them can be a challenge. If you have unhealthy grass (or grassy areas) you might want to treat it. The adults aren't a problem and birds love to eat them, and keep their numbers down for the most part. In rural areas they can be a problem in peak years.

Paracotalpa ursina

Unofficially this attractive beetle has been called the little bear beetle. Officially it is Paracotalpa ursina - which literally means the little bear Paracotalpa. And the bear is easy enough to imagine with the long setae (hair) and the plump body. The beetle belongs to the family Scarabaeidae - notice the fan-like antennae. It is a bit over half an inch long but seems bigger, especially as it climbs up grass stems and topples them over with its weight.

Jon and Michael found a population of the beetles last week in a city park here in Fresno and I went out yesterday to see them myself. There is something about a scarab in flight - with its elevated wing covers, low buzzing and erratic flight - that gets my beetle juices flowing. Museum specimens of this insect tend to be dull reddish brown. Live specimens have a much deeper red color. They're a sight to behold. Sadly, there were several along the park trail that had been smashed.

The place where the beetles were flying is not all that remarkable. It's maybe a quarter of a mile from the San Joaquin River and is just a fenced-off area with tall grass and a few other plant species. But that's often how you find interesting insects. They don't always live in the places we would consider ideal. And a grassy path in a park seems to be just fine for these brightly colored bruins.

Hoplia Beetles

There's a reddish brown beetle about the size of a large lady bug that you may have noticed on your roses or other flowers in the spring. Here in the Central Valley it shows up toward the end of April or the beginning of May and enjoys resting on velvety petals. If there are a lot of them, the flowers will end up with large areas of feeding damage, but this usually isn't the case. These insects only come out for a single generation a year and their first thought has nothing to do with eating, they are looking for mates.


These interesting insects are called Hoplia beetles. Their name is italicized because it is a generic Latin name – no American species in the genus Hoplia have common names. We have several species in the US and all of them can be recognized by the single large claw at the end of their hind legs. Other beetles have two claws (or occasionally none).


This is a picture of a mating pair of Hoplia dispar, on a blackberry blossom. It’s a common species in California. It is different from other Hoplia species in the shape of the fine white ornamental scales, which are strongly elliptical to almost round. Most other species have more elongate scales or no scales at all.


This side image of also of H. dispar. If you look closely, you can see that some of the scales are partially blue. This is an unusual color for insects but for some reason Hoplia beetles are sometimes colored this way. One very striking beetle is Hoplia caerulea from Spain that has its entire body covered with these pale blue scales (it’s worth doing an image search to see). It looks like a morpho butterfly version of a scarab.

So don’t be too alarmed if you find these beetles on your house plants. You can pick them off by hand and dispose of them if they become a problem. They do have the general appearance of Japanese beetles (though less colorful) but don’t do nearly the damage. One species (Hoplia philanthus) from Europe is known to be a pest in turf and pastures and may require a more aggressive control program. Here in the US, however, our species are much less of a problem.


This last image is Hoplia mucorea which is common in the mid-Atlantic states in the spring. It is less common than H. dispar but can be found in forested areas just as the leaves are starting to break out – around the time of the dogwood blooms. Watch for a small insect flying a foot or two above the forest floor. If you’re jogging or walking fast, you may miss them. They have a ponderous flight pattern because they only use one pair of wings to fly. The other wings (actually the forewings) are only wing covers (called elytra) and are held upright and out of the way of the flying wings. This makes for a slower flight, and in fact, you can often catch up with them and grab them with your hand. Don’t worry, they don’t bite. The worst the will do is give you a stout tickle you as they try and burrow between your fingers. Take a close look, they’re quite interesting and they’re out because it’s spring.