When people think of animals in Yellowstone, the “charismatic megafauna” usually jump to mind—beasts like elk, bison, wolves, moose, and bears (oh, my!). But the National Park is also home to a hearty collection of insects that have developed unique capabilities to thrive in Yellowstone’s extreme thermal environments!
Hot springs, cool beetles: Insects in Yellowstone go to extremes to survive and thrive
Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from Dr. Robert K. D. Peterson, Professor of Entomology at Montana State University, and Dr. Leon G. Higley, Professor of Entomology at the University of Nebraska.
The geology, chemistry, and microbiology of the thermal features in Yellowstone National Park have been studied for decades and are relatively well understood. But we know precious little about the insects that live in and on these thermal features. And, yes, some hardy insects do indeed inhabit these extreme areas!
One of these extremophile insects is an apex invertebrate predator known as the wetsalts tiger beetle, Cicindelidia haemorrhagica. Tiger beetles are voracious predators, and the wetsalts tiger beetle is no exception. Although this species inhabits moist saline flats in the western U.S., its presence in Yellowstone is unique because it is only found on hot springs. The immatures (called larvae) live in burrows in soil they construct immediately next to the hot springs, where they are sit-and-wait predators. Prey such as shore bugs, small spiders, and brine flies walk over the burrow entrances where the larvae spring out and grab them. The adult tiger beetles actively hunt by chasing down and subduing prey smaller than or as big as they are, including adult and larval brine flies and shore bugs.
Research studies conducted by scientists at Montana State University and the University of Nebraska have observed adult tiger beetles hunting on shallow water and soil surfaces with temperatures as high as 60 ºC (140 ºF) and a pH range from 2 to 12. Tiger beetles across the western U.S. often use behaviors to cool themselves during the day while they are hunting, and these behaviors can occupy as much as half their time. Examples include stilting at an angle with their long legs, seeking shade, and dipping their abdomens in water. But, amazingly, the wetsalts tiger beetles in Yellowstone behaviorally cool themselves much less frequently than their counterparts outside the park and that are not associated with hot springs, even though surface temperatures in Yellowstone are much higher.
This discovery is nothing short of astonishing. The population of a species of tiger beetle in this specialized, extreme habitat behaves very differently than a population of the same species in another habitat. The beetles behave differently, but is it only behavioral? Because Yellowstone beetles do not behaviorally cool themselves consistently during periods of increased temperature from sunlight and geothermally active soil and water, there must be some component to their physiology and genetic makeup that contributes to their heat tolerance or resistance.
In a series of laboratory and field studies since 2017, Montana State University and University of Nebraska entomologists systematically characterized behavioral, physiological, and physical responses between adult beetles in Yellowstone and a non-hot spring location in Idaho. Yellowstone beetles consistently have a lower internal body temperature than Idaho beetles with water surface temperatures of 40 ºC to 55 ºC (104 ºF to 131 ºF). This may indicate that the Yellowstone adult beetle has adapted to resist internal heating. Specifically, the increased heat resistance is the result of its adapted ventral abdomen that has enhanced reflectivity to infrared radiation––a heat shield, if you will.
The beetle’s adaptation is remarkable because the beetle has only been in Yellowstone––at most––since the Pinedale Glacial Icecap that covered most of the Yellowstone area with mile-thick ice receded 14,000 years ago. In other words, there has been relatively little time for these behaviors and body structures to diverge between the populations.
As much as we have learned, we do not know anything about the immature stage of the wetsalts tiger beetle. The areas where the larvae live are warm enough that snow instantly melts on them. The larvae may live one to two full years before becoming adults. How do they tolerate the hot, moist soil that also may be highly acidic or alkaline?
But the wetsalts tiger beetle it is not the only Yellowstone insect that is an extremophile. Shore bugs, brine flies, and soldier flies exhibit adaptations to the extreme conditions of the hot springs that have yet to be studied.
Extremophile animals in Yellowstone have much to teach us. Not only are they important for fundamental understandings of physiology, ecology, and evolution, but they relate directly to adaptations to climate warming and conservation. Furthermore, these extremophile animals can inspire advances in design, engineering, and materials. Yellowstone may be best known for the big animals, but some of the most surprising and fascinating animals are also some of the smallest!
(All research and photographs are per Yellowstone Research Permits #7092 and #8100.)
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