Ants in a Nutshell


Written by Curator Emeritus Bob Glotzhober

Some ants are nutty. More on that shortly.

In general, ants are truly amazing animals. The famed ecologist, E. O. Wilson, has estimated that all the ants in the world if placed on a balance scale would equal the weight of all the humans in the world. In some tropical areas, the biomass of ants equals 15 to 25% of the total terrestrial animal biomass. That is more than all the vertebrates in the area combined. Truly, ants are very, very numerous and highly diverse, with 22,000 known species world-wide. Ohio has 126 known species of ants. But without thinking about it, you already knew that! We see ants in our houses, in our gardens, on the sidewalks, and you cannot set down a picnic basket without ants inviting themselves to lunch! Ouch ants in our pants. Thank goodness no ants are the size of a dog.
 

You might assume that with so many ants in the world, that they would be very important ecologically. Remember, assumptions are dangerous! But this assumption would be right on target. Most ants are generalists, but some are strictly predatory, others are scavengers, others eat flower nectar, honeydew secreted by aphids, or seeds. Some ants harvest leaves to carry into their underground nests, but dont eat the leaves. In storage in the dark, damp environment, the leaves grow fungi and the ants eat the fungus! Their foraging may suppress populations of pest insects. Their tunnels and nests help aerate the soil. In Africa and South America, native peoples have learned to use large species of ants to close wounds. The flesh from a cut is squeezed together, and then a large ant is held close, and after biting the wound, the ants head is severed and the heads of several such ants remains holding the wound together as a natural suture!
 

Here in Ohio (and all over the world actually) some ants collect seeds from flowering plants. Over the past 110 to 130 million years ants and flowering plants have evolved together to form an amazing and jointly beneficial adaptation. Seeds of many of our spring wildflowers have an added structure attached to them known as an elaiosome. This is a sac rich in high energy lipids (fats). But neither the wildflower nor its seed makes any direct use of the elaiosome. Instead, foraging ants collect the seeds with the attached elaiosome and carry them underground into their nest. Here the ants feed the lipids to their larvae leaving the seeds in a perfect setting to germinate and grow. If the same seeds were left scattered on the surface they would either fail to germinate or be eaten by mice and birds. Ohio’s state wildflower, the Large-flowered Trillium, is just one of several spring wildflowers that benefits from this arrangement.

In 2005, Gary Coovert, now retired from the Dayton Museum of Natural History, completed and published through the Ohio Biological Survey his book, The Ants of Ohio. Ive heard Gary talk several times, and one of the fascinating things I’ve learned from him and his book is that there is a genus of ants known as Leptothorax that has several small species that utilize truly amazing nesting locations. One (Leptothorax ambiguous) uses empty goldenrod galls for a nest, while two others (Leptothorax curvispinosusand L. longispinosus) use hollowed out acorns. Most nests of these so-called Acorn Ants have about 83 worker ants and a single queen. Some have been found with multiple queens, and some with as many as 367 worker ants! We are talking about really tiny ants, typically 2 to 3 millimeters long. For those of you unaccustomed to the metric scale, a penny is about 1mm thick, and it would take from 8 to 13 of these ants lined end to end to measure one inch long.

Since I’ve learned about Acorn Ants, Ive started looking at acorns more carefully. This past September I was exploring Three Creeks Metro Park in Columbus when I noticed a lot of hickory nuts under a King Nut Hickory tree (Carya laciniosa, also known as Shellbark Hickory, or Big Shellbark Hickory). The nuts of these hickories are large, some as long as 1.5 inches. As I started to examine these nuts, I noticed one broken open and swarming with ants. Wow–had I found the famous Acorn Ants? As I looked closer, there were numerous tiny white granules in the recesses of the nut. Could the white, granular objects be larvae, meaning that this was indeed a nest? I scoped up the nut and examined it in my hand, then determined to carry it home where I could photograph it and perhaps get an ID on the ants. (Naturally, I didnt have my ubiquitous camera with me that day.) I had a mile plus walk to my car, followed by another half mile drive home and during that time only a few of the ants crawled up my arm or left the nut.

At home I examined the ants more carefully, as well as getting out my macro lens for close-up photos. Finding a suitable container to keep them alive but within the nut, I took them to work the next day to examine under the microscope. It turns out the white granular objects were not larvae, but ground up pieces of the meat of the hickory nut. This was not a nest. Gary Coovert identified the ants as the Thief Ant, Solenopsis molesta. Mixed in with a hundred or more Thief Ants was one lone ant of the species Prenolepsis imparis (no common name). Gary noted that this one different ant was missing both antennae and hypothesized that the Thief Ants were foraging both on the hickory meat and perhaps getting ready to also eat the lone intruding ant, which was almost double their size.
 

While I did not succeed in finding any Acorn Ants, these Thief Ants were fascinating in their own right. The Thief Ant is actually smaller than the Acorn Ant, at only 1.5 to 1.8mm long. Garys book says they are highly predacious, and nearly omnivorous. Hence one might expect them to eat both hickory nut meat and other ants. Further like the Acorn Ant, they are reportedly frequently found inside acorns, but foraging and not nesting in them.

Knowing that there are 126 species of ants in Ohio is only a small beginning. Their diversity of habitats and habits offer a lot of room for more studies, especially into their behavior and life histories. We are only beginning to learn the detailed ecology and life history for many of these species. So much to see and learn! Wow!

   

Bob Glotzhober

Senior Curator of Natural History

 

Posted January 22, 2013

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