Wildlife Profile: Beetles

Longhorned beetle Tragidion annulatum. Photo courtesy of Laura Pavliscak

Lately, we’ve been observing some sure-fire signs that Tejon Ranch has entered the dog days of summer: birds are rearing their young and singing less, most of our spring flowers have faded to brown, and of course, daytime temperatures are soaring. Although these more conspicuous phenomena may be ending for the season, this time of year is perfect for naturalists to shift their attention to one of the most diverse group of macroscopic organisms on the planet: insects. In particular, summer is an ideal period to be on the lookout for beetles.

Metallic green beetles (Genus Altica) and friends.

Chances are that everyone is familiar with at least a couple species of beetle (Order Coleoptera). From the seemingly ubiquitous “stink bug” (Eleodes gigantea) that places its hindquarters in the air when disturbed, to June beetles, fireflies, glow worms, and ladybugs (more appropriately called ladybird beetles), beetles are all around us. In fact, there are over 8,000 species of beetles in California For comparison, there are about 6,000-7,000 species of plant in the state (Evans and Hogue, 2006). That’s a lot of beetles.

But, how can you tell if the insect you are looking at is a beetle and not something else? Without getting too technical, there are some pretty straightforward guidelines that will help you identify the insect in question as a beetle. Refer to the figure below for an illustration of basic beetle anatomy. The most obvious field mark that identifies beetles is the straight line going down their “back” (more precisely, it’s the dorsal portion of the abdomen). This line represents the division of the elytra, or leathery wing covers. Although not every beetle is a particularly adept flier, the majority of beetles will have this line running down their back.

Compare the ladybird beetle below to the harlequin bug (Order Hemiptera- the true bugs) next to it. Although both look very similar in their morphology, the ladybird beetle clearly has the elytra division, while the harlequin bug has a more crisscrossed wing pattern. It’s a subtle difference, but very important.

Note the blue line pointing out the wing division in the beetle (left) and true bug (Order Hemiptera; right)

If you are close enough to examine a particular beetle, look carefully at its mouth. Beetles have chewing mouth parts, as opposed to the sucking mouth parts of true bugs (Hemiptera), flies (Diptera), butterflies/moths (Lepidoptera), and other insect groups. Even the beetles that appear to have a “snout”, such as weevils actually have chewing mouth parts.

Another interesting characteristic of beetles is their antennae. Throughout the insect world, antennae are used for a variety of purposes from feeling to complex chemical message receptors. While typically having 11 segments, beetle antennae can have fewer as well. Have a look at the diagram below to see a small sampling of the diverse antenna morphologies found in beetles.


Certainly this diversity must also translate to some functional diversity. Researchers have found the antennae of monarch butterflies to help them modulate circadian clocks, thus helping them navigate their migratory paths. Antennae are also used to stabilize flight in moths (Sane,Dieudonne, Willis, and Daniel 2007). Beetles display an incredible diversity of antenna morphology. A cursory search of the literature yielded evidence that beetle antennae can be sensitive to changes in electromagnetic radiation (Todorovic, et al. 2015) and aid in mating behavior (Ramsey, et al. 2015). Indeed, many beetles have sexually dimorphic antennae, where males and females have different-sized antennae. 

The ten-lined June beetle (Polyphylla decemlineata) is a species known to detect sexual pheromones through its antennae.

From a human’s perspective, beetles are extremely important because they can be pests, pollinators, decomposers, and even gardener’s friends! Knowing which beetle species is in your yard can be beneficial for the community at large. For instance, the golden spotted oak borer (“GSOB” Agrilus auroguttatus) is an invasive species that has been devastating oaks in Southern California. Researchers are trying to understand this invasion as quickly as possible to mitigate the beetle’s spread. Learn more about GSOB at UC ANR: http://ucanr.edu/sites/gsobinfo/.

 Next time you are taking a hike, or even enjoying the shade of a tree on a hot summer day, keep your eyes peeled for a beetle, one of nature’s most incredible and diverse creatures. You might end up realizing how fascinating and beautiful they truly are.

Western carrot beetle (Tomarus gibbosus obsoletus)

Pacificanthia consors, apparently a California endemic

Rusticoclytus nauticus

References:

Arthur V. Evans and James N. Hogue, Field Guide to Beetles of California  (Los Angeles: UC Press, 2006)

Wikipedia contributors, "Antennae," Wikipedia, The Free Encyclopedia, https://en.wikipedia.org/w/index.php?title=Antennae&oldid=414522334 (accessed July 3, 2015).

Wikipedia contributors, "Beetle," Wikipedia, The Free Encyclopedia, https://en.wikipedia.org/w/index.php?title=Beetle&oldid=669519380 (accessed July 3, 2015)