Here at the museum we've recently had the good fortune of several new donations to our collection. There are three donations in particular that I want to talk about, because of how they relate to a neat little system of snail versus beetle; and the evolution of Snail-Eater beetles.
For the first recent donation, we got a very large collection of shells from Dr. Mike Mather from the University of Arts and Sciences of Oklahoma, who is one of the best experts of Oklahoma mollusks and gave us a large set of shells from the Eastern United States. This is a very important donation because there are not that many opportunities to have shells identified by experts like him, so we are very lucky! While most of the shells are fairly large freshwater mollusks, many are also very very small.
New Zealand mud-snail, which is a problem in California; but you can see the small sizes these can come in! Especially when you compare to the Giant African Land snail from last week's post
How small these snails can be was even more apparent when I looked at how small the snails were for our next donation. Dr. Wyckoff, our former archeology curator, took part in a massive survey of land snails across a large portion of the United States, and is donating some of his snails to our collection over the next few years to compliment our existing collection and Dr. Mather's collection. Many of the shells are just as small as the picture above, and show just how diverse many of these snails can be in size, shape, and location across North America. Its this diversity that makes the next group of invertebrates I'll talk about such a neat group: how they've managed to evolve mouth parts to feed on snails.
An example of variation in snails; this case color variation
With so many different snails out there and many of them in pretty good supply, there has been a group of beetles called the Snail-Eater Beetles that have evolved to feed on them. Snail-Eater Beetles belong to the predatory group of beetles called Carabidae, or Ground Beetles, and primarily feed on snails, slugs and the occasional banana (for some reason bananas make good traps for these beetles).
A small Purple Snail-Eater Beetle from Le Flore Co., Oklahoma. This specimen is now part of our collection thanks to the donation of Dr. Vitt and Dr. Caldwell. Unfortunately the picture doesn't get the metallic purple of their Purple name.
The "Purple" of the Purple Snail-Eaters. This image and the following image are from Bugguide.net
These beetles are some of my favorites not just because of their pretty purple color, but their unusual mouthparts. This brings us to our last donation of several thousands of insect specimens by Dr. Laurie Vitt and Dr. Jan Caldwell, of the SNOMNH Herpetology department. In addition to the very well-curated and preserved specimens from Oklahoma, Arizona, New Mexico and Florida, their donation included two of these neat, unique, and pretty little beetles. Both specimens are from Le Flore County, and are pretty small: about 4-5cms.
When I would find these guys in Virginia (my home state), many were much larger than this species. Therefore, the first thing I thought when I saw these little guys was there has to be a correlation with their small size and the snails they feed on here in Oklahoma. After all, the shape of their heads and mouthparts have to do with what sized snail they are trying to get.
Snail-Eater sticking its head into a snail shell to get its prey
In fact, these beetles have mouthparts especially "designed" to open snail shells from the front. However, there is a trade-off to having a smaller head to fit inside the shells, especially the tiny-tiny ones. According to a study highlighted in this article, the evolutionary trade-off occurred from the wide-headed, strong-jawed general Carabidae family to the slender, can-opening shape of the Snail-Eaters. At some point in time, it was more beneficial to switch from crushing snails shells to actually getting the head into the opening (operculum). As a result of this, one group of beetles evolved down this track of having a head-shape that will get into a snail shell instead.
"Can-opening" shape of Snail-Eater jaws
Related Carabidae; that head won't fit into a snail shell for sure!
Carabid relative eating a crushed snail
So, just as there is a wide variety of snail sizes and morphologies, there is a wide-variety of beetles that have evolved to take advantage of these snails. And thanks to the recent donations to our collection, we have examples of both group's diversity!
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