South Dakota's High Plains Tiger

(Amblycheila cylindriformis (Say))

[First published in South Dakota Conservation Digest, March/April 1996]

Amblycheila cylindriformis (Say) ambling along.
Photo by P.J. Johnson, 1995)

Exploration of the sagebrush and shortgrass steppe of the western High Plains, at night might seem low on the have-to-do priority list for most people. However, a nocturnal perambulation in the open range and bluffs of Fall River County, especially around Angostura State Park or near Cascade Falls, will allow the diligent naturalist to observe one of the oddest, and largest, entomological subjects in South Dakota.

Known scientifically as Amblycheila cylindriformis (Say), and herein dubbed the High Plains Tiger Beetle, this insect reaches a length upwards of 35 mm and is one of the largest insects of the Great Plains. Taxonomically, as a beetle, it is a member of the insect order Coleoptera, and is in the tiger beetle family Cicindelidae. In general, tiger beetles are active predators and scavengers on other insects, and as such they are beneficial by their feeding on many pest species. Their moniker of tiger beetle refers to their predatory voracity.

The High Plains Tiger Beetle was first formally described to science in 1823, by Thomas Say, one of the first American entomologists. The first specimen known to early explorers was discovered by Say in what is now eastern Colorado, while he was on an extended military and natural history exploration of the "Arkansa" region, the then Missouri Territory. The second specimen known to entomologists was not discovered until 1852. Until the 1870's, this species was rarely collected and was much sought after by wealthy European and American aristocrats.

During the late 19th Century the compilation of natural history collections was a significant status builder among the wealthy elite and provided the founding core for many of the larger private collections and public museums in Europe and the United States, such as the Carnegie Museum in Pittsburgh. A story in the September 30, 1897 issue of the Philadelphia Record newspaper noted the exploits of two private collectors that succeeded in acquiring a number of specimens. These entrepreneurs were able to sell individual beetles for upwards of $50 or more apiece for live specimens, earning $10,000 that year. Fortunately, this species was thereafter found to be much more common and widely distributed than originally supposed, thus considerably dropping market values and permitting its survival.

In general, tiger beetles tend to be medium sized insects (ca. 15-20 mm in length) and often possess bright colors. Several species common in western prairie habitats have bright metallic red elytra (wing covers) sharply contrasting with metallic green or blue heads and other body parts. Occasionally, these colors are mixed in various patterns that vary with the angle of light reflection. Some other species are dull black with small iridescence spots, or flat green with ivory-white slashes; most species possess some pattern of ivory-white markings on their elytra. Most commonly seen species inhabit dry areas in the prairies, sand hills, and mountains, preferring the open areas in grasslands and meadows, trails, and even dirt or gravel road sides, burms, and cuts. Other species are restricted to exposed banks and sand dunes along rivers.

The majority of tiger beetles are diurnal, being most active on warm sunny days from snow-melt in the spring through the autumnal killing frosts, while hiding in protected areas on cooler days or when clouds obscure the sun. These beetles can frequently be seen flying off several feet in front of the hiker to land further-on as they try to avoid ones feet. This flight behavior makes them a real challenge for the observer, photographer, and collector! Contrastingly, the High Plains Tiger Beetle is a somber jet-black throughout and is nocturnal. Too, it cannot fly, as it has evolved a strictly ground-dwelling habit and lost its wings and the natural predilection to fly. Consequently, this beetle more resembles its common ground beetle cousins in behavior, than its tiger beetle sister species. Despite the flight impediment, the High Plains Tiger Beetle is an effective predator and scavenger on grasshoppers and other insects, including the large prairie lubber grasshopper, Brachystola magna. In Fall River County this beetle was observed attacking and eating a wide variety of grasshoppers and crickets, various kinds of darkling and common ground beetles, spiders, cutworms, and ants. In the laboratory, they have never turned down any kind of arthropod meat that has been offered to them and seem to prefer grasshoppers and crickets.

The life cycle of the High Plains Tiger Beetle remains poorly understood. Fortunately, disparate bits and pieces of information are beginning to reveal a few interesting inferences, such as overlapping generations and extended larval life spans. For example, in Fall River County, the adults are in their peak of activity during the last couple of weeks of June and the first couple of weeks in July. Rough surveys during this time period suggest populations upwards of 100-120 High Plains Tiger Beetles per acre. Following this peak there are gradually decreasing numbers of individuals through late August. Only the occasional individual will overwinter as an adult. Rather large, 3.5-4.0 mm long, cream-white eggs are laid singly in the soil, from which the hatchling larva will tunnel into the soil and begin forming vertical burrows in which it will spend most of its life. An individual may remain as a larvae for at least a 1-2 years, before pupating and developing into an adult that would live for only a couple of months, at best.

Larvae of the High Plains Tiger Beetle are large, elongate, grub-like creatures that spend their entire developing stages in deep tubular burrows that may extend 2-3 feet into the soil. These burrows are difficult to locate and distinguish from the multitude of other 6-8 mm diameter holes in the ground along trail edges, or at the base of roadcuts and low bluffs. The entrances are circular and evenly formed. During the day the larvae stay deep in the burrow, but as evening progresses they move to the surface entrance of their burrow and await any other insect that wanders within reach. Though initially startled by lights and best observed in the outer halo of a flashlight, with care and patience the observer will see a brownish head blocking the burrow entrance. As if from a modern science fiction movie, this monstrous flush-to-the-ground head bearing a pair of strong black scythe-like mandibles are held agape, awaiting food. With the arrival of an unsuspecting cricket, June beetle, or other edible item, the larva will rapidly dart itself partway out of the burrow and snap its mandibles deep into its victim, dragging it down into the burrow for feeding. Excavated burrows of older larvae will have a plug of inedible carcass remains packed below the larva's resting area. Rapid body extensions for and retraction with prey is accomplished by sets of strong longitudinal muscles in the body and a pair of large forward-arching dorsal hooks at the midlength of the abdomen. These hooks are used for grappling the inner surface of the burrow and prevent struggling prey, or a predator, from pulling the tiger beetle larva from its burrow. How much a larva will eat is unknown, but in the laboratory individuals will eat at least 2 adult house crickets per day.

Adult High Plains Tiger Beetles are also nocturnal, becoming active about sunset. On warm nights their activity continues well into the morning hours, but they will seek hiding places before sunrise. Most tend to find rodent or other burrows to hide within during the day. Occasional individuals can be found under stones, within thick grass tussocks, or under debris, such as discarded wood fence posts. At night, the beetles appear to wander randomly, but they are directed in their attention for food and mates. Nearly blind with but remnant eyes, they pay little heed to flashlights or lanterns. Instead, these beetles rely more on tactile sensations than vision for detecting their environment. They search with their antennae held downward and outward in front at approximately 45 degree angles to feel for their prey, and can also detect prey movement through vibrations picked-up by sensitive hairs on their feet. When prey is detected the beetle rapidly pounces upon its victim, grabbing with its mandibles, and begins chewing immediately. The large sharp mandibles bear several strong teeth for tearing and shredding. A hapless grasshopper will be rendered quickly and rarely escape with the loss of only a leg or two. These tiger beetles will also hang around ant nests, often standing amidst the swarming ants and literally grazing through the crowd.

Interestingly, a beetle that feeds on ants will follow a minute or two of feeding with a curious pushing of its mouthparts through loose sand for several seconds. This intriguing behavior may help to remove formic acid and other defensive chemicals that the ants exude, or assist in cleaning the mouthparts of remnant particles, a sort of toothbrushing between meals!

Mates are located through tactile senses, with the males expending most of the effort in their search for females. Male-male encounters are usually uneventful, though on occasion a short struggle may develop. Typically, these encounters are little more than a bit of pushing and flailing with legs and a snap or two of their mandibles, but rarely last for more than a few seconds. Occasionally, one or both of the jousters will lose part of an antenna or leg with their roughhousing. If a male encounters a female, then a surprisingly short courtship ensues that consists of only a few seconds of his antenna gently touching her body. Should the female be receptive, the male will become excited with rapid movements of his legs, antennae and mandibles. This momentary frenzy is followed by mounting and grasping the female with his mandibles about the base of her pronotum. However, rather non-chalantly and not to miss necessity, the female will continue to slowly hunt and feed while the male rides along, though some pairs will remain stationary for an hour or longer.

As with most insects the females live considerably longer than males with the latter living a mere few weeks, while females may live for several months until the end of the season. With plenty of food and water, laboratory specimens have lived to mid-November, resulting in a nearly 5 month adult lifespan.

To date, the High Plains Tiger Beetle has only been found in South Dakota on the low southern flanks of the Hogback ridge surrounding the Black Hills, and along the Cheyenne River. The closest other known sites are near Manville, Wyoming, and Scotts Bluff, Nebraska. All of the known sites in our region are sagebrush steppe or shortgrass prairie in their original vegetation. Extensive disturbance of rangeland through cultivation, including crested wheatgrass plantings, markedly changed the vegetation in Fall River County, but the local beetle populations appear to have survived in those areas extensive with remaining natural vegetation. Development of Angostura Reservoir and the State Park provided an incidental opportunity for conserving beetle habitat. The beetle's presence helps to indicate the potential for natural reacquisition of native communities under appropriate management.

Though globally threatened, but not endangered, the High Plains Tiger Beetle was widely distributed from the Texas panhandle and adjacent New Mexico though the high plains of Colorado, Oklahoma, Kansas, Nebraska, to Wyoming and South Dakota. In the last 100 years, this beetles' habitats and populations continue to diminish and become more fragmented. Like most other species this beetle suffers more from removal of large areas of contiguous steppe habitat than local catastrophic decimation. The loss of habitat is undoubtedly the primary cause for reduction or loss of most High Plains species. As with most of our High Plains flora and fauna, unregulated human population growth and expansion of suburban development lead the charge for their demise. We do not have enough information to estimate the size of our Fall River County populations, but the tiger beetles are at least holding their own in a few pockets. This allows the curious naturalist an opportunity to see another natural wonder in South Dakota.

Distribution of A. cylindriformis in the southern Black Hills.

Copyright © Paul J. Johnson, 1997