Wild Species 2005: chapter 6

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Tiger Beetles

Tiger Beetle - Any flesh-eating beetle of the family Cicindelidae - The Canadian Oxford Dictionary.

Quick facts

• There are more than 2600 species of tiger beetles in the world, of which 30 have been found in Canada.
• Tiger beetles belong to the family Cicindelidae and are closely related to the ground beetles (Family Caribidae).
• The majority of Canada's 30 species of tiger beetles (70%) have a Canada General Status Rank (Canada rank) of Secure but 17% have Canada ranks of May Be At Risk and 7% have Canada ranks of Sensitive. 3% of species have Canada ranks of Not Assessed. No tiger beetles of Canada ranks of At Risk, because COSEWIC has not yet assessed any tiger beetles.
• Tiger beetles are aptly named for their predatory nature and the stripes that many of them wear.
• The Bronzed Tiger Beetle 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

Tiger beetles (Family Cicindelidae) are well named for their predatory nature and the colourful stripes that many of them wear. Due to their large size (relative to other beetles), striking colours, and fascinating behaviour, tiger beetles have been fairly well-studied in Canada, making them a good choice for the first family of beetles to be ranked as part of the general status program. Most tiger beetles are classified as habitat specialists because they use very specific habitat types. Many species live in areas with sparse vegetation and undisturbed soil, such as sand dunes, salt flats, beaches, bare hillsides, sparse prairie habitat and forest openings.

Adult tiger beetles are recognizable by their large compound eyes, wide head and long antennae, as well as their large, sickle-shaped jaws which they use to capture and eat their prey. Like all adult beetles, tiger beetles have two pairs of wings. At rest, the fragile hind wings are hidden beneath the protective sheath of the hardened forewings, or elytra. When the beetle takes flight, the elytra open to allow the hind wings to propel the beetle through the air. Many adult tiger beetles have very striking colours and patterns; the elytra, head and legs can be stripped or spotted with bright metallic greens, blues and reds. The colourful markings actually act as camouflage for the adults, allowing them to blend into the background, so it is usually movement, rather than colour that gives away the location of a tiger beetle.

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.

Tiger beetles are creatures of the sun; they need the warmth of the sunlight to keep their body temperature high enough to maintain their active lifestyle. Even a cloud passing across the sun will stop a tiger beetle in its tracks. To escape bad weather or the cool of the night, tiger beetles dig a shallow tunnel in the ground. To pass the winter, tiger beetles dig a much a longer tunnel, up to 2m deep! The tiger beetle fills in the tunnel behind it and remains at the bottom of the tunnel until the ground warms the next spring.

Tiger beetles have four stages in their life cycle; egg, larva, pupa and adult. Eggs are laid singly in carefully chosen soils, where the moisture and humidity will provide the correct environment for the egg and the developing larva. Once hatched, the larva quickly digs a vertical tunnel deep into the soil. The s-shaped larva resembles a caterpillar, except that the large head is fixed at right angles to the body. Like the adults, tiger beetle larvae are superbly adapted predators, feeding on ants and other small arthropods. The larva waits at the entrance of its tunnel, with its large head blocking the entrance and its huge jaws opened wide. When a prey item comes in range, the larva reaches out at lightening speed to grab its prey. The larva has two curved hooks on its back; if the struggles of its prey threaten to pull it out of its tunnel, the larva jams these hooks into the wall of the tunnel to maintain its position. When the prey is subdued, the larva drops to the bottom of its tunnel with its prey, to enjoy its feast in private.

When the larva is large enough, it retreats into its tunnel, and metamorphoses into a pupa. Pupae do not eat or move; their sole purpose is to undergo the changes that will allow an adult to emerge. In a few weeks, the pupa metamorphoses into an adult tiger beetle, which emerges from the tunnel to begin life on the surface.

Status of knowledge

Due to their interesting behaviours and striking colours, and because they are usually active during the day and are fairly easy to observe, tiger beetles have been better studied than most other families of insects. There is even a scientific journal devoted solely totheir study. Tiger beetles have been used to study such varied topics as sight, thermal ecology and predator avoidance techniques. However, although the life history of tiger beetles in general is well known, life histories of specific species are often less well known, and in particular, there remain many questions about their movements between suitable habitats (dispersal). In addition, there remains much to be discovered about the distribution of Canadian tiger beetles, particularly in terms of the limits their occurrence.

Due in part to their global distribution, well established taxonomy, their specific habitat needs and the relative ease with which they can be identified, tiger beetles are being considered as possible indicators of biodiversity (the diversity of life in all its forms) on a global scale. In this role, tiger beetles are likely to become increasingly important to scientists, conservationists and managers, both within Canada and worldwide.

Richness and diversity in Canada

Twenty-eight of the 30 Canadian tiger beetles belong to the genus Cicindela, colourful beetles that are active during the day. The other two beetles belong to the genus Omus. This genus is restricted to the costal region of western North America, and includes species that are flightless and active only at night. Tiger beetles are found in every province and territory except Nunavut, but species richness is highest in the prairie provinces (Figure 2-5-i, Table 2-5-i). British Columbia has the most species that are found nowhere else in Canada (five species).

Species spotlight - Ghost Tiger Beetle, Cicindela lepida

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 May Be At Risk.

Species spotlight - Six-spotted Tiger Beetle, Cicindela sexguttata

Unlike most tiger beetles, which tend to inhabit sparsely vegetated, open habitats, Six-spotted Tiger Beetles, Cicindela sexguttata, live on the floor of deciduous forests. This presents Sixspotted Tiger Beetles with a problem: how to maintain a body temperature high enough to sustain their active lifestyle? In the open habitats where most tiger beetles live, there is an abundant supply of sunshine, and tiger beetles bask in the sun to raise their body temperature to the required level, but on the forest floor, sunlight is in short supply. In order to survive in the forest, Six-spotted Tiger Beetles have a lower optimum body temperature than other tiger beetles. In addition, Six-spotted Tiger Beetles spend most of their time in patches of sunlight, created along trails or where trees have fallen over, where temperatures are warm enough for Six-spotted Tiger Beetles to maintain their optimum body temperature. In contrast to other tiger beetles, which chase down their prey over relatively long distance, Six-spotted Tiger Beetle wait within their patch of sunlight, until a prey item comes close enough for them to pounce.

Six-spotted Tiger Beetles have a two year life cycle; females lay eggs in the summer, which hatch into larvae. Larvae overwinter in their tunnels, and pupate around mid-summer of their first year. Adults may briefly emerge at this time, but then overwinter in their tunnels once more, before emerging as sexually mature adults, early the next spring. Within Canada, Six-spotted Tiger Beetles are found in Ontario, Quebec, Nova Scotia and New Brunswick, and they have a Canada rank of Secure.

Results of general status assessment

The majority of Canada's 30 species of tiger beetle species have Canada ranks of Secure (21 species, 70%, Figures 2-5-i and 2-5-ii, Table 2-5-i). However, 17% have Canada ranks of May Be At Risk (five species) and 10% have Canada ranks of Sensitive (three species). No species has Canada ranks of At Risk, because no COSEWIC status assessments of tiger beetles have been completed. Finally 3% of species have Canada ranks of Not Assessed (one species).

Threats to Canadian Tiger beetles

Tiger beetles 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. In addition, human recreational use of tiger beetle habitat can kill larvae and disturb the habitat of the adults.

Conclusion

Although tiger beetles have been better studied than many other insect families, much remains to be learned about the range and status of tiger beetles in Canada. The potential role of tiger beetles as indicators of biodiversity may act as an impetus for their further study in Canada and around the world.

Further information

Acorn, J. H. 2004. Grassland tiger beetles in Canada. Arthropods of Canadian Grasslands [PDF, 1.49 MB] 10:6- 14. (Accessed September 15, 2005).

Acorn, J. 2001. Tiger beetles of Alberta. Killers on the clay, stalkers on the sand. University of Alberta Press, Edmonton. 120 pp

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 September 15, 2005).

Leonard, J. G. and Bell, R. T. 1999. Northeastern tiger beetles: A field guide to the tiger beetles of New England and eastern Canada. CRC Press, Boca Raton. 176 pp

Marshall, S. 2000. Tiger beetles of Ontario. (Accessed September 15, 2005).

Pearson, D. L., Knisley, C. B. and Kazilek, C. J. 2005. A field guide to the tiger beetles of the United States and Canada: Identification, natural history, and distribution of the Cicindelidae. Oxford University Press, Oxford. 292 pp

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

Young Entomologists' Society. 1998. Tiger beetle world. (Accessed September 15, 2005).

Wallis, J. B. 1961. The Cicindelidae of Canada. University of Toronto Press, Toronto, Ontario. xii + 74pp

References

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

Barber, K. Ed. 1998. The Canadian Oxford Dictionary. Oxford University Press. Toronto, Oxford, New York. 1707 pp

Headstrom, R. 1977. The beetles of America. A.S. Barnes and Co. Inc. Cranbury, NJ. 488 pp Hilchie, G. J. 1985. The tiger beetles of Alberta (Coleoptera: Carabidae, Cicindelini). Quaestiones Entomolgicae 21:319-347

Pearson, D. L. and Cassola, F. 1992. World-wide species richness patterns of tiger beetles (Coleoptera: Cicindelidae): Indicator taxon for biodiversity and conservation studies. Conservation biology 6(3):376-391

Schultz, T. D. 1998. The utilization of patchy thermal microhabitats by the ectothermic insect predator, Cicindela sexguttata. Ecological Entomology 23(4):444-450

Stanton, E. J. and Kurcaewski, F. E. 1999. Notes on the distribution of Cicindela lepida Dejean (Coleoptera: Cicindelidae) in New York, Ontario and Quebec. The Coleopterists Bulletin 53(3):275-279