Wild species 2010: chapter 13

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Insects: Ground beetles

Carabidae - Family of insects in the Coleoptera order. These species are generally dark-coloured, long-legged, predatory beetles with thread-like antennae. Tiger beetles (Cicindelidae) represent a sub-family of the ground beetles.

Quick facts

• There are more than 30 000 species of ground beetles in the world, of which 934 have been found in Canada.
• When excluding species ranked as Extinct, Extirpated, Undetermined, Not Assessed, Exotic or Accidental, the majority (88%) of ground beetles in Canada have Canada General Status Ranks (Canada ranks) of Secure, while 6% have Canada ranks of Sensitive and 6% have Canada ranks of May Be At Risk. However, it should be noted that the many of the ground beetle species were ranked as Undetermined.
• Three species are ranked as At Risk following a detailed COSEWIC assessment. They all are tiger beetle species.
• A total of 54 Exotic species were found among the ground beetles in Canada.
• Ground beetles are aptly named as most are found at the surface of the soil. However, a few Canadian species are usually found running on herbaceous plants and even on trees.
• Ground beetles are active, usually fast-running predators that vary in size from tiny (1.4 mm) to impressively large (30 mm). The Bronzed Tiger Beetle (Cicindela repanda) can run at speeds up to 0.5 meters per second; taking body size into account, that is 10 times faster than the fastest human sprinters!

Background

All species of ground beetles are assessed for the first time in the Wild Species series. However, the tiger beetles (Cicindelidae) were first assessed by the National General Status Working Group in the Wild Species 2005 report. Since most authorities now classify tiger beetles as belonging to the ground beetle family (Carabidae), we have included the reassessment of the tiger beetles in the ground beetles section of the Wild Species 2010 report.

Ground beetles are commonly seen from the spring melt of snow until the first snows of winter. Individuals can easily be found under leaves and rocks in the middle of winter after removing the snow cover. Adult ground beetles are a little difficult to characterize in a few words. They have long legs and are excellent runners. They also generally have rather long, thread-like antennae. Few ground-dwelling beetles in other families show these features. Some darkling beetles (Tenebrionidae) look like ground beetles, but their hind legs have only four tarsal segments, whereas ground beetles have five segments. Darkling beetles are common in dry regions, but otherwise are uncommon in Canada. Except for tiger beetles, most ground beetles have a clear pattern of long furrows in their wing covers (elytra). Adults vary greatly in size (from 1.4 to 30 mm) and in colour patterns, though most are black or brown. Because they don’t generally fly and can be found hiding under objects during the day, these beetles are one of the easiest insect groups to find even under very inclement weather conditions.

Most ground beetles are fast-running species. For example, adult tiger beetles are voracious predators, locating prey by sight and giving chase across the ground at astonishing speeds of up to 53 body lengths per second (about 10 times faster than a top human sprinter!). But rather than chasing prey continuously, tiger beetles often pause momentarily during the chase before continuing at full speed once more. Scientists now believe they know the reason for this stop-start method of pursuit. At the high speeds that tiger beetles achieve while chasing their prey, light cannot enter the eye fast enough to form an image of the moving prey item; at high speeds the tiger beetle goes temporarily blind! Pausing during the pursuit allows the tiger beetle to relocate its prey, while its incredible speed still allows it to complete the chase successfully.

Ground beetles are generally known as predators, but the reality is a little more complex – the food range is quite wide. Most predators are opportunistic as they also commonly scavenge dead insects and drink from mature fruits. Most predators are generalists, but in a few groups they specialize in certain types of prey. For instance, species in the genus Calosoma feed exclusively on caterpillars (hence their common name, caterpillar hunter) and those of Scaphinotus hunt only snails and slugs (hence the name snail beetles). The herbivores fall basically into two groups: the seed collectors (various species of Harpalus) and the plant tissue feeders (various species of Amara). In addition, many plant-dwelling species are commonly seen feeding on flower nectar. The plant dwellers may be predatory but flower nectar, like mature fruits, may be very attractive. Larvae follow generally a similar pattern as described above, but species of Brachynus (bombardier beetles) are external parasites (“parasitoids” is a better term as the larva kills its host) of whirligig beetle (Gyrinidae) pupae, and those of Lebias are external parasites of leaf beetle (Chrysomelidae) pupae. Ground beetles are mainly active at night. However, there are exceptions in such a large family – many species (for example, some in Bembidion and Amara) are diurnal.

Ground beetles go through four developmental stages in their life cycle; egg, larva, pupa and adult. Eggs are laid singly in carefully chosen soils or even under bark of trees, where the moisture and humidity will provide the proper environment. Newly-hatched larvae move away from the egg shell and soon look for food. Larvae of predatory species have very long and very sharp, needle-like mandibles. Anything of proper size that moves is potential food, including their siblings. Dispersing soon after hatching is crucial for these larvae! All Canadian species that have been studied go through three larval stages, or instars. The development of spring-breeding species is fast and is completed within one month from the time the eggs have been laid, whereas that of the summer breeding species is much longer as they must overwinter before completing their development. At the end of the third larval instar, the larva stops feeding, becomes lethargic, and usually builds a cell in the soil. This is the prepupal stage. When ready, the prepupa molts again and a white pupa emerges and remains on its back. Pupal development is usually fast and soon the new adult emerges from the pupa with a pale, soft cuticle. In a few days the cuticle hardens and darkens. Among the spring-breeding species, adults may remain within the pupal cell until the following spring, or may run for a few weeks in the early fall without breeding. Among the summer-breeding species, the new adults immediately run out to feed and look for mates.

Adults of all species are found over a long period of two to six months. Larvae of spring-breeding species complete their cycle within one month, while adults commonly live two to five years. Larvae of summer-breeding species usually take one year to complete their development and overwinter before transforming, and adults of most of these species do not live beyond one breeding season. Adults commonly winter under rocks and other moderate-sized debris, under leaves and under bark of dead trees, or deep in the soil (species of Calosoma and Chlaenius). In Canada, overwintering is a special and necessary inactive stage for most ground beetles. This stage is called a diapause. Adults of most spring-breeding species need to go through diapause before they will start breeding. The overwintering larvae of summer-breeding species need to go through diapause in order to continue development. The warming trend in the spring causes the end of the diapause period.

Status of knowledge

Relative to most insect groups, ground beetles are well understood and most species are known and described. The Canadian list is relatively stable, although new species are occasionally discovered and classifications are occasionally changed. Many amateurs and scientists have built large reference collections of this very diverse group across Canada. The most significant reason, however, is the extraordinary work initiated by C. H. Lindroth (1961 to 1969), who published on the complete fauna of ground beetles of Canada and Alaska. George Ball and his students at the University of Alberta also added many significant revisions to complete Lindroth’s work. But even forty years after Lindroth’s publications, there are surprisingly few changes to his concepts. Other studies, such as the numerous publications of André Larochelle (for example: Larochelle and Larivière, 2003) and more recently the book of Bousquet (2010), also represent important works. But are there places for new discoveries? The answer is an emphatic “Yes.” The study of ground beetles of Canada is now on another level of understanding. The undiscovered species are cryptic, requiring careful observations and studies to be recognized. The first clue is in nature, because most species of ground beetles have special life cycle and habitat requirements, but more recently the use of new genetic methods of investigation have uncovered previously unknown species.

Despite the relatively good understanding of which species live in Canada and how to recognize them, there is much to be discovered about the details of their biology. Here, our knowledge is only basic. By analogy, we have the dictionary of Canadian ground beetles, but now there is a need to explore beyond definitions. We need to explore the details of their biology and the interactions with other species in various ecosystems. Adults have been used often as biological indicators in various habitats. As indicator species, we know that each species is sensitive to habitat disturbances and modifications, to the use of pesticides, and to introduced species. All these factors strikingly affect the species composition of ecosystem.

Richness and diversity in Canada

Canada’s 934 species are classified into 126 genera. The largest genera are Bembidion (174 species), Pterostichus, Agonum, Amara, and Harpalus. Ground beetles are found in all provinces and territories, as far north as Devon Island (Amara alpina). Moving southward, diversity increases near tree line and species number increases rapidly in the cold temperate zone, and reaches the maximum in southernmost Ontario and southwestern British Columbia. Unfortunately, these last two regions are the two most affected by human activities.

Species spotlight - Vietinghoff’s Ground Beetle

A preconception about northern insects is that they are small, black and probably all related to mosquitoes. Vietinghoff’s Ground Beetle (Carabus vietinghoffi) is probably one of the most elegantly coloured species of ground beetle in Canada, and is also one of the largest. This species is found in both Asia and North America, with its distribution centered on the Bering Sea. In Canada, it is recorded from western Nunavut (Kugluktut), Yukon and Alaska, from just north of tree line south into the central portions of the boreal forest. The southernmost record is from the banks of the Pelly River, Yukon, about 150 kilometres north of Whitehorse. The females are spring breeders and seem associated with moderately drained sites with trees or bushes. This species has a general status Canada rank of Secure.

Species spotlight - Poecilus lucublandus

This quite elegant species, which has no official common name, is coloured yellow green on the head and the pronotum and purple on the wing covers, all set off with metallic reflections. It is found across Canada from central boreal regions southward. In spring, it is a typical insect of gardens and lawns – adults like moderately moist soil. Adults breed in the spring, larval development takes place in summer and new adults run in early fall but do not breed. Adults overwinter under debris and rocks. Adults and larvae are nocturnal predators; they probably consume fly larvae and other soft-bodied invertebrates in the soil. In day, adults are found easily under rocks and wood pieces. When disturbed during the day, they run very rapidly to a dark spot or a small hole or crack in the soil. Because of their association with human habitats, they are often found in agricultural sites.

Species spotlight - Ghost Tiger Beetle

The Ghost Tiger Beetle (Cicindela lepida) is a small tiger beetle found on undisturbed white sand in coastal and lake-shore sand dunes, as well as inland sand dunes and sand flats. Within Canada, the Ghost Tiger Beetle is found in the prairie provinces and in Ontario and Quebec. Ghost Tiger Beetles are pale in colour, with faint brownish markings on the elytra, making it difficult to see against the sand. When predators approach, the Ghost Tiger Beetle freezes against the sand and relies on its camouflage to protect it from detection. In fact, its camouflage is so good, that the beetle’s shadow is often easier to see than the beetle itself, leading to its unusual name. The life history of the Ghost Tiger Beetle has been described as unique among tiger beetles because the larvae live for two years, over-wintering twice, while the adults only live for about one month!

Although the Ghost Tiger Beetle can form large populations in suitable habitat and is thought to be able colonize new habitat fairly easily, local populations are vulnerable to habitat loss due to human development or to natural succession and to disturbance by heavy recreational use of their habitat. This species has a Canada General Status Rank (Canada rank) of Sensitive.

Results of general status assessment

A large portion of Canada’s 934 assessed species of ground beetle have a Canada rank of Secure (545 species, 58%, figure 13 and table 18). However, 36 species (4%) have a Canada rank of May Be At Risk, and also 36 species (4%) have a Canada rank of Sensitive. Three species are ranked as At Risk following a detailed COSEWIC assessment; they all are tiger beetle species.

Finally, 260 ground beetle species (28%) have a Canada rank of Undetermined, and 54 species (6%) are ranked as Exotic in Canada.

Comparison with previous Wild Species reports

Since only the tiger beetles were assessed in a previous Wild Species report, the comparison will be made only for the 31 species of tiger beetles. Since 2005, the category of species ranked as At Risk had the highest increase in terms of number of species (table 19). All these species were previously in the category of May Be At Risk, and were changed following detailed COSEWIC assessments (table 20). A total of five species had a change in their Canada rank since the last assessment. Among these changes, three species had an increased level of risk and one species had a reduced level of risk. One species of tiger beetle was also added to the national list in 2010.

Threats to Canadian ground beetles

Ground beetles, like other insects, are vulnerable to habitat loss and disturbance due to natural succession, changes in drainage patterns, erosion control and conversion of natural habitat for human uses. However, a more pressing concern in areas with large human populations is the use of pesticides. In Europe, it has been shown that all kinds of pesticides affect ground beetle populations negatively. In our region, insecticides are fast acting, but herbicides have a similar but slower impact on wild populations of numerous species associated with agricultural lands and lawns. Around Ottawa and Montreal over a period of one or two decades, many agricultural sites showed a marked population decrease; up to 60% of the species has been affected. Some common to very common day-active and spring-breeding species have not been captured in the past 25 years. Moreover, even in sites without pesticide use, the diversity of ground beetles clearly has been affected by herbicides from adjacent sites. The effect is such in these areas that the diversity of sites without history of pesticides is similar to that of sites with pesticides.

A new source of problems is associated with several species of alien earthworms in forest habitats in agricultural regions of Ontario and Quebec. Twenty to thirty species of ground beetles are normally expected in deciduous forests. In most sites, 100% of forest-inhabiting ground beetles are absent or near absent. However, two alien ground beetles, Carabus nemoralis and Pterostichus melanarius are abundant. Adults of the last two species feed on any earthworms (all are exotic in the region under study) while those of native forest species feed on fly larvae and probably other soft body insects. The original food of the native species was simply replaced by earthworms that compost the leaf litter within one year, with disastrous consequences that extend well beyond the ground beetles diversity.

Conclusion

Much remains to be learned about the biology and distribution of many ground beetle species. The status of ground beetles associated with southern agricultural regions (where the diversity was formerly the greatest) is of great concern. These beetles have been shown as important indicators of ecosystem health.

Further information

Acorn, J. H. 2004. Grassland tiger beetles in Canada. Arthropods of Canadian Grasslands [PDF, 1.49 MB] 10: 6-14. (Accessed April 14, 2010).

Carabidae of the World. 2009. Online Database. (Accessed February 26, 2010). [Avaiable in Russian only]

Freitag, R. 1998. Catalogue of the tiger beetles of Canada and the United States. Ottawa NRC Research Press, Ottawa: 195 pp.

Goulet, H. and Bousquet, Y. 2004. The ground beetles of Canada. (Accessed February 26, 2010).

The Tree of Life Web Project. 2008. Carabidae. (Accessed February 24, 2010).

References

Alcock, J. 1976. The behaviour of the seed-collecting larvae of a carabid beetle (Coleoptera). Journal of Natural History 10: 367-375.

Balduf, W. V. 1935. The bionomics of entomophagous Coleoptera. John S. Swift, New York.

Bousquet, Y. 2010. Illustrated identification guide to adults and larvae of Northeastern North American Ground Beetles (Coleoptera: Carabidae). Pensoft Series Faunistica #90, Pensoft Publishers, Sofia-Moscow: 562 pp.

Cassola, F. and Pearson, D. L. 2000. Global patterns of tiger beetle species richness (Coleoptera: Cicindelidae): their use in conservation planning. Biological Conservation 95: 197-208.

Frank, J. H. 1971. Carabidae (Coleoptera) of an arable field in central Alberta. Quaestiones Entomologicae 7: 237-252.

Freitag, R. 1979. Carabid beetles and pollution. In Carabid beetles: their evolution, natural history, and classification (T. L. Erwin, G. E. Ball, and D. R. Whitehead, editors). Dr. W. Junk, The Hague, Netherlands.

Larochelle, A. and Larivière, M.-C. 2003. A natural history of the ground-beetles (Coleoptera: Carabidae) of America North of Mexico. Pensoft Series Faunistica #27, Pensoft Publishers, Sofia-Moscow: 584 pp.

Lindroth, C. H. 1961-1969. The ground-beetles (Carabidae, excl. Cicindelinae) of Canada and Alaska, part 1-6. Opuscula Entomologica Supplementum 20: 1-200; 24: 201-408; 29: 409-648; 33: 649-944; 34: 945-1192; 35, I-XLVIII.

Lund, R. D. and Turpin, F. T. 1977. Carabid damage to weed seeds found in Indiana cornfields. Environmental Entomology 6: 695-698.

Rainio, J. and Niemela, J. 2003. Ground beetles (Coleoptera: Carabidae) as bioindicators. Biodiversity and Conservation 12: 487-506.

Thiele, H.-U. 1977. Carabid beetles in their environments, a study on habitat selection by adaptation in physiology and behavior. Springer, Berlin, Germany.

Marshall, S. 2000. Tiger beetles of Ontario. (Accessed April 14, 2010).

Pearson, D. L. and Vogler, A. P. 2001. Tiger beetles: The evolution, ecology and diversity of the Cicindelids. Cornell University Press, Ithaca, New York: 333 pp.

Schultz, T. D. 1998. The utilization of patchy thermal microhabitats by the ectothermic insect predator, Cicindela sexguttata. Ecological Entomology 23: 444-450.

Wallis, J. B. 1961. The Cicindelidae of Canada. University of Toronto Press, Toronto: 74 pp.