The Cobblestone Tiger Beetle

Cobblestone Tiger Beetle. Photo by Stephen Krotzer, used with permission.

by Mischa Giasson

In 2008, l was asked to participate in a mark-release-recapture survey on the shores of Grand Lake, New Brunswick. My dad and I joined Fredericton entomologist Reggie Webster on a boat to visit three small sites among the rocky beaches surrounding the lake. We were searching for a rare, recently locally discovered beetle that is found nowhere else in Canada: the Cobblestone Tiger Beetle. This experience was the first of many that lead me to the realisation that a career in entomology was an option, fueled by my life-long fascination with insects (and other creepy-crawlies).

The Cobblestone Tiger beetle (Cicindela marginipennis) is an insect in the sub-family Cicindellidae (Coleoptera: Carabidae). This small, pretty beetle is listed as Endangered and placed in Schedule 1 of the Species at Risk Act (SARA), which means that the species has been deemed at risk and that there has been development and implementation of protective and recovery measures.

There is no doubt that Tiger Beetles live up to their namesake as extremely beautiful, but equally deadly predators. These beetles run down their prey by sprinting in short, quick bursts. In fact, they run at such high speeds that they temporarily go blind! One species has been recorded moving at 9 km/hr, which is almost 54 times its body length per second. Their antennae are used to prevent any collisions while sprinting and they have a very short reaction time, but they must make frequent stops to take in their surroundings and make sure they’re on the right track.

Both the adults and larvae are predators, the larvae employing a sit-and-wait approach: they wait in ambush from small vertical burrows in the ground, striking out at lightning speed to catch any prey that passes nearby. Prey consists of other insects as well as spiders, which stand no chance against the huge mandibles of the Tiger Beetle. The Cobblestone Tiger Beetle can be distinguished from other Tiger Beetles by the smooth, continuous cream-coloured border along the outer edges of the elytra and by a bright orange/red abdomen that is visible when the beetle is in flight. Their overall colour is most often a dark chocolatey brown, but some metallic blue and green individuals have been observed in the New Brunswick populations.

Cobblestone Tiger Beetle. Photo by Stephen Krotzer, used with permission.

The Cobblestone Tiger Beetle gets its name from its choice in habitat. The eight sites in New Brunswick where it can be found are all cobblestone beaches. This beetle is also found along major river systems in the United States, from Mississippi to Alabama and from Indiana through to New England. Populations are quite small, few and far between. The Canadian population was discovered in 2003 by Dwayne Sabine and is the only known population to also inhabit lakeshore sites, likely due to the riverine characteristics of Grand Lake. There are three known sites on Grand Lake, while the other five are on the shores of small islands in the Saint John River between Woodstock and Bath. These cobblestone habitats are unique to areas with yearly spring flooding which keeps the vegetation from spreading along the beach, maintaining the flat areas of gravel and sand between the stones which are necessary for the larvae to make their burrows. Not much is known of the Cobblestone Tiger Beetle’s specific life history, but it is assumed to be similar to that of other tiger beetle species. The beetles have a two-year life cycle: eggs are laid individually in the sand, where the larvae will hatch and make burrows. The larvae overwinter in their burrows, somehow surviving the spring floods and emerging as adults in June.

Cobblestone Tiger Beetle. Photo by Stephen Krotzer, used with permission.

Due to their specific habitat requirements, Cobblestone Tiger Beetles are very vulnerable to environmental changes and disturbances. The biggest threat is habitat damage. In New Brunswick, the installation of the Mactaquac dam destroyed many suitable habitats both upstream and downstream. The small beetle populations are also quite vulnerable to over-collection by scientists and insect enthusiasts. The current concerns involve the use of off-road vehicles, as this leads to the alteration of suitable habitat and often directly leads to the death of many larvae present on the beaches. This threat applies mostly to the shores of Grand Lake, where there is increasing development and use of the beaches. The protective measures implemented include developing a stewardship plan, educating the local communities and encouraging their support and participation in the conservation of this special beetle. Decreasing human disturbance is the most important factor in ensuring the survival in our province of the already very small populations of the Cobblestone Tiger Beetle.

References

https://www.registrelep-sararegistry.gc.ca/virtual_sara/files/plans/rs_cobblestone_tiger_beetle_e_final.pdf

http://www.sararegistry.gc.ca/species/speciesDetails_e.cfm?sid=1031

Zurek, D. B., & Gilbert, C. (2014). Static antennae act as locomotory guides that compensate for visual motion blur in a diurnal, keen-eyed predator. Proceedings of the Royal Society of London B: Biological Sciences. 281(1779): 20133072.

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