May 13th and Darwin was still recovering from his injury – hanging out in the cabin with his pal Augustus. The remainder of his entry for the day relates to the weather and the curious nature of the reverse of the seasons in the Southern Hemisphere. Darwin writes:
“This is the winter season; a great deal of rain falls, but chiefly by night; in other respects the weather is most delightful & cool. — The temperature in a room generally varies from 70°–75°.” (May 11/12/13)
Darwin’s entries this week are rather sparse, so I thought I’d try something a little different – a theme week. So in honor of one of Darwin’s favorite group of animals, this week is:
(Hey, if Shark Week is a big success on the Discovery Channel, why can’t Beetle Mania Week make the big time!) By the way, the topic is not totally random. During May and June, while staying in Rio, Darwin collected and identified several different beetle species. It is those descriptions in his Zoological Notebook that are the inspiration for the week of blogs. I thought I’d start with a little beetle “primer”.
Beetles (collectively placed in the Order Coleoptera) make up about 1/5 of all identified living things on Earth (as mentioned in my first beetle post a couple of weeks ago – Whirligigs in a Ditch). Coleoptera belong the Class Insecta, in the great Phylum Arthropoda (which includes not only all insects, but also crabs, lobsters, isopods, spiders, mites, horseshoe crabs and the extinct trilobites).
There are several suborders within the Coleoptera, however, most beetle species (about 90%) are found in the Polyphaga (“eaters of many things”) suborder, with the majority of the remaining beetles found in the Adephaga (“gluttonous”) suborder. (The “Volkswagona” suborder of beetles had not been created in 1832.)
Currently nearly 400,000 species of beetles have been identified, though many more remain unidentified. Conservative estimates suggest that there are probably between about 1 and 4 million beetle species on Earth (and not-so-conservative estimates place that number as high as 100 million).
The defining characteristic of beetles is summed up by their name – Coleoptera. Koleos is Greek for “sheath” and pteron means “wing”, and beetles (by definition) have a “sheathed wing”. So what does that mean? Well in most beetles the front wings (the elytra) are hardened into a shell-like sheath that encase the rear wings (the alea) and the abdomen of the beetle.
Beetle anatomy of a fiddler beetle (from Wikipedia Commons)
Once you get past the similarity of the armored elytra (and the other characteristics shared by all insects, such as having 6 legs and 3 body sections) you’ll find that the variety of beetles found around the world is astonishing. They are found virtually everywhere on Earth, collectively eat almost anything you can think of, and come in a wide range of shapes, sizes, and colors. The wide range of beetle adaptations boggles the mind – from “scuba tanks” to chemical warfare systems, beetles have it covered it all.
To start off our beetle menagerie, let’s look briefly a one family of beetles Darwin mentions s few times – the tiger beetles (Subfamily Cicindelinae). Tiger beetles below to the Carabidae Family (from the suborder Adephaga (see diagram below)
Tiger beetles truly are the “tigers” of the beetle world. Like tigers they are predatory, aggressive and can run really fast.. and I mean really fast. The fastest species have been clocked at 5 ½ miles per hour. Granted that does not sound like much, but if you scale that up to our size, a human would have to run 480 mph in order to keep up with one of these beetles. Talk about a scary predator!
Cicindela ohlone in the United States (from USFWS via Wikipedia Commons)
Some beetles mimic other types of insects – either to make it easier to find food, or to make themselves look less appetizing (or more threatening). One tiger beetle from Brazil has even evolved to look like an ant.
Tiger beetle from Brazil (from What’s That Bug?)
By the way – the Beetle Mania! title is my concoction, though the beetle images all come from Wikipedia Commons and the appearance by the one of the Fab Four is from the cover album by The Liverpools released in 1964 called “Beetle Mania! in the USA”. (RJV)