Beetles and Ants: Strange Bedfellows?

Until January 5, 2014, the Canadian Museum of Nature is featuring a photo exhibition on ants—a very diverse group of insects. Even though ants are not exactly my area of expertise, I can still field a few technical questions on the subject. That’s why I was asked to join in the preparation of the Farmers, Warriors, Builders: The Hidden Life of Ants exhibition.

Almost a dozen ants crawl on the ground.

One of the photos from Farmers, Warriors, Builders: The Hidden Life of Ants. Taken in Gabon, this image shows worker ants from the Crematogaster genus crawling in all directions. Image: © Mark W. Moffett/Minden Pictures

At our team meetings, my entomologist colleague Robert Anderson and I started talking about insects that are sometimes found living among ant colonies.

It is generally thought that ants are aggressive and attack everything they can get their jaws on. However, in the course of their evolution, several insect species have succeeded in adapting to life among ants. They do this to flee predators, take advantage of resources left over by the ants, and even feed on ant eggs and larvae. Of course, this is by no means an exhaustive list of the complex interactions between ants and their roommates, or inquilines, as they are called in the scientific jargon.

Of all the insects that live among ants, the most frequently observed are probably beetles. Representatives of several beetle families have adapted to life among ants. One species in particular remains ingrained in my memory.

In 1991, I was a new recruit at the Canadian Museum of Nature. A colleague working in South Africa at the Transvaal Museum (now part of the Ditsong Museums of South Africa) invited me on an expedition. This gave me the opportunity to go on a one-month insect hunting trip in what was then Transvaal Province.

One of the first places we visited was a farm near the Limpopo River. I was testing ways of making the most of light traps. I must admit that we were at the right place at the right time: the rainy season was just beginning, and the trap (a lighted bed sheet) was attracting a good number of beetles.

A bed sheet hangs on a line strung between two trees.

This light trap was made from a white bed sheet strung between two trees and lit up using a projector.

The normal procedure requires that you edge up to the sheet, choose the interesting specimens, and drop them one by one into vials. This method frustrates me to no end because it is inefficient, especially when you are swarmed by thousands of insects trying to creep into your clothes and tickle you. You also have to watch out for beetles getting into your ears (perhaps even perforating your eardrum), and keep away from vesicating insects (also known as poisonous insects) that secrete toxins capable of producing sizeable blisters.

All these issues were resolved thanks to two simple tricks: place the containers below the sheet, and spray insecticide over the sheet to make the bugs fall directly into the containers. All I had to do was empty the containers into alcohol from time to time. I went back to the lab with litres of my very own “insect soup”.

Because this technique does not allow you to study the captured insects right away, the real hunt begins in the lab when you put a spoonful of “insect soup” in a Petri dish and start examining it methodically under the binocular loupe. That’s when you fully grasp the meaning of the term biodiversity!

A man uses a microscope to examine the contents of a Petri dish.

Back at the lab, François Génier analyzes the contents of the “insect soup” that he collected during fieldwork. Image: © Canadian Museum of Nature

Now begins the task of sorting through the lot in search of a rare specimen. Time stands still as the brain functions at high speed, analyzing and trying to identify each one of the species under scrutiny. Once a complete set of species has been extracted from the sample, the specimens can be prepared and studied individually.

I don’t remember exactly when, but one little beetle ended up catching my eye. At first glance, I couldn’t identify which family it belonged to. I finally concluded that it was a ground beetle belonging to the Carabidae family. This large family includes some tens of thousands of species that are fairly easy to recognize. The flat oval shape of the bug that I had just found was quite peculiar, though, and for good reason: it was most likely a myrmecophilous insect—that is, one that lives among ants.

The entire sample of some 20 000 specimens contained only one such specimen from that particular species. I now knew this specimen belonged to the Pseudomorphinae sub-family, and I sent it to my colleague Martin Baehr. If my memory is correct, he responded rather quickly by asking me if I was not mistaken on the provenance of this particular insect.

I told him there was no way of mistaking the provenance. This was indeed the first known specimen from the Carabidae sub-family on the African continent! Martin Baehr, who at the time was revising the taxonomy of this group, explained that my discovery was not only unprecedented on this continent, but it helped draw important conclusions on the origin of these insects, which were previously known to live only in America, Asia and Australia.

A beetle.

François Génier was to first to observe the Cryptocephalomorpha genieri beetle in Africa. He collected the specimen in 1991, in what was then Transvaal Province, South Africa. Collection #CMNE 00011496. Image: François Génier © Canadian Museum of Nature

In recognition of this, Mr. Baehr named the species Cryptocephalomorpha genieri after my family name—Génier. Since then, two other specimens have been reported, one in Botswana and one in Zambia, clearly indicating that the species is widely distributed in southern Africa.

Species of the Cryptocephalomorpha genus are exceptional because rather than lay eggs, these beetles give birth to larvae, which are more mobile in case of an attack from the ants. This appears to be one of their adaptations to life among the ants. The morphology of the larvae is also more complex than that of an egg. Larvae may have glands that can secrete scents to hide their presence or stave off the ants.

Translated from French.

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