Sat. Jan 28th, 2023

When army ants invade the jungles of Costa Rica, they leave behind death and destruction. These nomadic group predators eat everything from centipedes to other ants, and they even raid wasp nests for eggs and larvae. Any insect that does not escape the swarm of hundreds of thousands of ants is likely to die a horrible death. And yet many insects have evolved to live among army ants, feeding on their leftovers and even sheltering in their nests.

Researchers Christoph von Beeren and Alexey K. Tishechkin just identified a tiny beetle that they named Nymphister kronaueri who keeps track of the endless march of the army ants in an unusual way. N. kronaueri clamps itself with its lower jaws on the back of an army ant, as if it were a soldier going into battle on the back of the most beautiful horse in the world. Von Beeren and Tishechkin describe the strange life of N. kronaueri in a newspaper BMC Zoologyand they explain how these animals evolved to live among creatures that would normally gorge themselves on their beetle guts.

Insects and other creatures that live among ants are mentioned myrmecophiles, which literally means ant lovers. Myrmecophiles benefit greatly from this strange relationship. They can certainly feed on the remains of the colony after a raid, but there’s more to it than that. Ants create a pleasant environment, much like a human city that attracts wildlife. The researchers write:

Life in and around ant colonies is expected to be beneficial for arthropod guests, especially those who have managed to get along well with ants. Among the latter are highly integrated species that inhabit ant nests, in which they are protected from their own predators, live in a stable microclimate and have access to rich food resources.

Because ant colonies are such nice places to live, myrmecophiles evolved early. Some species have followed ants for 50 million years.

Hierboven zie je <em>N. kronaueri attaches to the ant’s back and uses its jaws to grab between the second and third segments of the ant’s body.  Below is a close-up of the beetle’s clamped mandibles.” src=”×480.jpeg” width =”640″ height=”480″ srcset=”×961.jpeg 2x”/><figcaption class=
Enlarge / You see above N. kronaueri attached to the ant’s back and uses its jaws to grab between the second and third segments of the ant’s body. Below is a close-up of the beetle’s clamped mandibles.

A) Daniel Kronauer, B) Munetoshi Maruyama

N. kronaueri is a small beetle with a hard, hairy shell. It has only been observed in the army ants of Costa Rica, where von Beeren and Tishechkin studied them exhaustively. The researchers monitored the behavior of six different ant species at the La Selva Biological Station. When it folds its antennae and legs tightly against its carapace, the dark brown insect resembles one of the elongated segments in an ant’s body. This similarity may be an evolutionary adaptation. The beetles have a chitinous shell whose texture resembles that of an army ant, which can trick the army ants into accepting it N. kronaueri like a friend when they touch and smell them.

Like many other myrmecophiles, N. kronaueri probably gain favor with their ant hosts by smelling good. Ants navigate the world by touch and smell, and they recognize nest mates by smelling the oils on their bodies. Often, the researchers write, beetles “take advantage of their glandular chemistry, which contains defensive and ant-feeding compounds, that allow them to interact with host ants.” They secretly mingle in ant colonies by smelling and feeling like they belong there. Naturally, N. kronaueri is also constantly looking for trouble. The hairs covering its body are sensory organs tuned to minute changes in vibration and pressure. These hairs probably help N. kronaueri navigate densely populated ant nests without sounding the alarm.

Survival is only a matter of clever disguise N. kronaueri when the army ants are in their stationary phase, which lasts up to a month while the eggs hatch. But then the ants enter a nomadic phase, where they roam the jungle eating everything in their path and sleeping in temporary bivouacs every night. Keeping up with the raging horde is difficult for a beetle, even though this is when it probably ingests the most food scraps each night. Hence N. kronaueri‘s unique method of riding the ants: The beetle clambers onto an ant’s back before locking its jaws onto the ant’s “waist”, between the thorax and gaster. Then N. kronaueri pulls all six of its legs into specialized grooves in its shell for the rough ride.

N. kronaueri aren’t the only insects that hitchhike on ants like this one: other beetles have been known to cling to ants’ underbelly and ride upside down. Still others cling to grubs or food, which the ants pick up and carry in their jaws on their daily march. But N. kronaueri seem to be the only beetles that have figured out how to ride like cowboys. They even have a favorite size of steed, generally picking medium sized ants to carry them.

Topafbeeldingen zijn <em>N. kronaueri</em>, seen from all sides.  Below are images of the beetles’ genitalia, used to identify the new species.  e through l are male sex organs;  m and n are feminine.  ” src=”×465.jpeg” width=”640″ height=”465″ srcset=”https ://×930.jpeg 2x”/><figcaption class=
Enlarge / are top images N. kronaueri, seen from all sides. Below are images of the beetles’ genitals, used to identify the new species. e through l are male sex organs; m and n are feminine.

BMC Zoology

Researchers von Beeren and Tishechkin identified the new beetle species first by observing their unique behavior, but then by using close anatomical research and DNA analysis. It turns out that if you want to know which beetle you’re dealing with, the best place to start is with the genitals. So the two were carefully dissected N. kronauerigenitals and compared them with other species. They found what appeared to be a unique configuration.

DNA analysis also confirmed a new species. Interestingly enough it seems N. kronaueri also has very low genetic diversity. The researchers speculate that “one possible explanation is a recent genetic bottleneck, perhaps due to a recent dispersal event followed by the expansion of a small genetically uniform founder population, a population genetic pattern typical of invasive species.”

Von Beeren and Tishechkin write that in their paper N. kronaueri is just one of many species of myrmecophiles that live mysterious lives among ants, much as crows, squirrels, and raccoons live among humans in cities. Because they live in sprawling colonies, ants are a particular target for “guest” species that want the protective environment created by an ant community, as well as the food scraps. Yet most of these ant-loving animals have never been studied. “We have no idea how they live or why they associate with ants,” von Beeren and Tishechkin write.

The more we learn about our environment, the clearer it becomes that animals continually engage in complex relationships that we are only just beginning to understand.

BMC Zoology2017. DOI: 10.1186/s40850-016-0010-x (About DOIs).

Frame image by Daniel Kronauer

By akfire1

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