An Assortment of Beetles

For as long as I can remember, I've loved arthropods. Arthropods come in so many different shapes, sizes, and colors, and even one group can exhibit an incredible amount of variation. One has to look no further than the beetles to see this in action. Beetles are insects that belong to the order Coleoptera, and there are a ton of beetle species out there. An inconceivable amount really. Just how many beetle species do we know about? There are currently 400,000 described species of beetles in the world, which accounts for around 25% of all the described species on Earth. For comparison, there are only about 5,400 described species of mammals in the world, and only about 10,000 described species of birds in the world. And that 400,000 number only accounts for the described species of beetles, which means the individual species some scientist has officially described as a species separate from the others. That number isn't including all the species we currently don't know about. Some scientists have estimated that there might be a total of 1,000,000 to 2,000,000 beetle species in the world, meaning there are hundreds of thousands of species out there waiting to be discovered and described!

Beetles exhibit a tremendous variety in both appearance and lifestyle. Some are all black, while others can resemble a rainbow. Some are carnivorous, while others are herbivorous, while even some others are omnivorous. Some are solitary, while others are relatively social. Some beetles provide parental care, and some navigate their landscape using the stars. Much of the allure of beetles lies in the sheer diversity regarding every part of their biology.

Despite the variety in form and function of beetles, I've never really spent too much time looking at their world. I have, however, collected many pictures of beetles over the past 5 years, and so I've finally decided to dive in and write up a post on a few of those species. This post is organized by family, so let's jump in to one of the more speciose families.

Carabidae

The family Carabidae—whose members are commonly called the ground beetles—is incredibly diverse, with over 40,000 described species. Many of the Carabids are darkly colored, but a good number are colorful and metallic. One such example is the species pictured above, Chlaenius aestivus. Because there are so many species of beetles in the world, many of them do not have common names, instead only having a scientific name. Chlaenius aestivus—as well as many of the other species included in this post—does not have a species-specific common name, but the collective common name for members of the genus Chlaenius is "metallic ground beetle." The name is rather fitting, isn't it?

My favorite group within the family Carabidae—and the beetles as a whole—are the tiger beetles. Although there are over 2,600 species of tiger beetles described in the world, the US and Canada is home to only about 117 species. The most recognizable species in Ohio is without a doubt the vibrantly-green Six-Spotted Tiger Beetle, but I want to talk about two other species. First up is the Eastern Red-Bellied Tiger Beetle, Cicindela rufiventris. I came across this individual while visiting Steve Willson's Blue Jay Barrens in Adams County, Ohio. As a side note, Steve operates a fantastic blog on the nature and management of the cedar barrens on his property. You can read his blog at Blue Jay Barrens! As with many other tiger beetles, the Eastern Red-Bellied Tiger Beetle prefers sunny openings in forests which can occur along ridgetops, near rock outcrops, and in recently disturbed areas.

Another tiger beetle which calls Ohio home is the One-Spotted Tiger Beetle, Cylindera unipunctata. I found this individual after it came to the lights during a mothing night at Clear Creek Metro Park in southeast-central Ohio. When it comes to the world of arthropods, tiger beetles are fearsome predators. They are lightning-fast, and the fastest species—Cicindela hudsoni—can reach speeds up to 5.5 miles per hour. Proportionally, if humans could run that fast, we would be running at speeds around 225 miles per hour! In addition to their speed and agility, they also have large, formidable jaws that can easily clamp onto a prey item, such as other beetles, small flies, and a host of other arthropods.

Pyrochroidae

This orange and black beetle is Neopyrochroa flabellata, one of the flame-colored beetles of the family Pyrochroidae. Contrary to what one might assume, the reproductive habits of insects can be much more complex than "find a live individual of the opposite sex and mate." And N. flabellata has a rather fascinating love life. Many animals love to eat eggs; eggs are little bundles of protein and nutrients which don't fight back. Normally, at least. When female N. flabellata's lay their eggs, they cover the eggs in a protective compound called cantharidin. Cantharidin is a blistering compound that causes burns when applied to the skin of an animal, and can poison an animal in large enough doses. As such, covering your eggs in cantharidin would ensure that no one else messes with them. The problem is, N. flabellata can't make their own cantharidin.

So how does the female get it for her eggs? Well that's where the males come in! The job of the male is to find and consume enough cantharidin, and then approach the female. Upon approaching a female, a mating ritual will ensue. The two beetles will face each other, head to head. The male will begin to secrete part of his cantharidin reserve from a special gland found on his head, and the female will use her antennae to sense whether the male does indeed have any cantharidin, and if so, does he have enough. If he lacks it all together, he will almost surely be rejected. If he has some, but not a lot, he runs the risk of being rejected as well. If the female thinks he male has enough, she will then signal that she is willing to mate. During the mating process, the male transfers his cantharidin to the female, who will then coat her eggs with it.

Where does the male get the cantharidin, you might be wondering? That's a good question, and there's some uncertainty when it comes to the answer. Cantharidin is a rare substance in nature, and only two groups of beetles—the blister beetles of Meloidae and the false blister beetles of Oedemeridae—can synthesize it themselves. It is currently assumed that male N. flabellata individuals will seek out blister beetles and either kill and eat parts of their body to accumulate the cantharidin, or that they scavenge on dead blister beetles to get the cantharidin. There's a few issues with this premise, as Thomas Eisner et al. points out in their 1996 paper on the subject. First, it hasn't been recorded that N. flabellata feeds on adult insects, such as the blister beetle. Second, blister beetles and false blister beetles rarely occupy the same habitats that N. flabellata occupies. And lastly, it seems unlikely that there are enough blister beetles out there to satisfy the need of N. flabellata individuals. The question of the source of the canthardidin highlights the lack of often basic information we have on so many of our arthropod species.

Lucanidae

As I mentioned with the previous beetle, we are lacking a lot of the "basic" facts when it comes to most of the arthropods on Earth. Take, for example, the beetle above. This is a Ceruchus piceus. There isn't a lot that's known about Ceruchus piceus, especially when it comes to random interesting facts. It is worth pointing out that the individual pictured is a male, as can be told by its large mandibles. This species belongs to the family Lucanidae, which is commonly known as the stag beetles. As male deer have a part of their body enlarged to attract females and fend off other males, so too do male beetles of the family Lucanidae. Male deer have antlers, but male stag beetles have large mandibles. These mandibles are used to attract females, fight other males, and defend themselves from potential predators. 

Scarabaeidae

It wouldn't be a post about beetles without throwing in one of the scarab beetles. A few scarab beetles—which are simply beetles of the family Scarabaeidae—are well-known to humans. May Beetles (AKA June Bugs), Green Fig Beetles, and dung beetles are all different types of familiar scarab beetles. But my favorite scarab beetle is one of the lesser-known species. Meet the Grapevine Beetle, Pelidnota punctata. The Grapevine Beetle is a large and relatively common species across the eastern US, but one that not many are familiar with. That is unless you happen to be a moth-er, as Grapevine Beetles love to come to mercury vapor lights. As the name suggests, the adults of this species feed on the various species of wild and domesticated grapes found throughout the eastern US. Despite this, the Grapevine Beetle is not considered a significant pest species. 

Chrysomelidae

In my opinion, one of the most under-rated families of beetles is Chrysomelidae. Chrysomelids—more commonly known as the leaf beetles—are beetles that feed exclusively on plants. Generally speaking, they are relatively small, round, and oftentimes colorful. Take, for example, the Milkweed Leaf Beetle, Labidomera clivicollis. As the name implies, this species feeds on various milkweed species, especially Swamp Milkweed, Asclepias incarnata. Like the Monarch butterfly and other insects which feed on milkweed, the Milkweed Leaf Beetle sequesters the cardenolide toxins found within the plant for defense. And as with the Monarch, the Milkweed Leaf Beetle has a colorful and contrasting orange and black coloration to warn predators of its poisonous nature. 

Cerambycidae

Beetles in the family Cerambycidae are almost always attention grabbers. Species of this family are collectively called long-horned beetles—and often for obvious reasons. As the Eutrichillus biguttatus individual pictured highlights, the Cerambycids typically—although not always—have long antennae that are normally as long as their body. Sometimes, such as with E. biguttatus, the antennae are much longer than their bodies. 

Although some of the long-horned beetles are subdued in color for camouflage, others can be fantastically colored. Take the Elm Borer, Saperda tridentata, for example, with its flame-colored oranges contrasting with its deep black. Long-horned beetles often get a bad rap among us humans, as many of their feeding habits result in them being labelled pests. Generally speaking, the larvae of long-horned beetles feed on wood. Depending on the long-horned species in question, this wood can be dead wood or—as in the case of the Elm Borer—live wood. For the species whose larvae feed on live trees, an infestation can result in the direct or indirect death of the tree. Of course, this might upset some people when the tree in the yard dies, but all is part of the natural balance within a forest (except, as I should point out, when it comes to non-native invasive long-horn beetle species. Such invasive species can cause significant harm). The native Elm Borers, for instance, almost always choose weak, broken, or sickly elm trees to lay their eggs in. Healthy elm trees are apparently left alone. With such a lifestyle, Elm Borers are actually inadvertently culling sickly elm trees from the forest while leaving the healthy individuals to proliferate.

Silphidae

The most exciting beetle I've seen my entire life has been—without a doubt—the American Burying Beetle, Nicrophorus americanus. The American Burying Beetle is a federally endangered species which has all but disappeared from its range across the eastern and central US. I learned about it years ago, and never thought I would get to see one because of how rare it is. However, I was lucky enough to visit The Wilds this past summer and help with a reintroduction of over 200 captive raised individuals. Not only did I get to see American Burying Beetles, but I also got to hold some! I have an entire post up on the strange life cycle of the American Burying Beetle, some of the most current thoughts as to cause of the decline of the species, and the reintroduction efforts by The Wilds. You can find that post right here at this link!

Typically, I end my blog posts with the species I was most-excited to see, but not this one. Today, I will end with a species who has evolved a lifestyle unlike all of its cousins. Meet Nicrophorus pustulatus, another member of the burying beetle family. Like the previous American Burying Beetle, almost all burying beetles (genus Nicrophorus) follow the same general reproductive pattern: First, they find a carcass of some sort, then they bury that carcass within a chamber underground, then they modify the carcass into a meatball covered in anti-fungal anal secretions, and then they feed parts of that carcass to their young, which they laid in a chamber right above the carcass-ball. But not N. pustulatus. This species has evolved a rather remarkable alternative lifestyle. Nicrophorus pustulatus is a parasitoid of snake eggs. A parasitoid is a specific kind of parasite that actually ends up killing its host. Parasitoids are extremely common in the invertebrate world, but they all utilize other invertebrate as hosts. Nicrophorus pustulatus is the only invertebrate parasitoid currently known of in the world whose host is a vertebrate!

In the early 2000's, a team of scientists kept noticing that the Black Rat Snake nests they were finding regularly contained both adult and larval N. pustulatus individuals. Within these nests—which often contained many separate clutches of eggs as these snakes regularly nest communally—many of the eggs had been obvious consumed. When the team of scientists looked into this phenomenon, they realized that no one had ever documented N. pustulatus burying carcasses before in nature, and they began questioning whether there was something unusual going on. They soon found that if you raise N. pustulatus individuals in the lab, and give them a dead mouse, they will bury that mouse, but they seemingly didn't do so in nature. A few studies later (the original in 2000 and a confirmation in 2007), and it can safely be said that N. pustulatus is indeed a parasitoid of snake eggs, a wholly new and remarkable phenomenon in the natural world!

Last fall, I purchased a macro lens with the intent to take more detailed photos of various arthropods, and hopefully I will take many more photos of beetles. If I do, you'll surely see some more posts on this diverse group! Thanks for reading!