Sprinter, hunter, player
Neither a glamorous creature nor a pest, the playful tiger beetle is an understudied insect despite its fascinating ways.
By Jean Godawa
After basking on a narrow blanket of sandy soil in the late-morning sun, the tiny creature stood up and stretched its legs. As I walked forward, my quarry ran away – not far, just a few metres ahead – then turned to face me, as if daring me to follow. I did, and the game continued. Such behaviour is typical of tiger beetles and those of us curious enough to want a closer look.
Beetles have fascinated us for thousands of years. Ancient cultures worshipped them; international organizations study and protect them; people even wear them as living jewellery. Found in almost every habitat, beetles are the largest animal group on earth, comprising well over 300,000 species. Their wide range of food sources (from rotting corpses to flower petals) and their almost limitless variety of sizes, colours and shapes also distinguish them. Despite this multiplicity, beetles are easily recognized by one feature: the elytra, a pair of hard forewings that meet in a straight line down their backs, protecting the more delicate and membranous hindwings underneath. Tiger beetles’ elytra is especially spectacular, varying in colour and pattern from the iridescent green of the common six-spotted tiger beetle (Cicindela sexguttata) to the perfectly camouflaged, mottled appearance of the rare, sand-dwelling ghost tiger beetle (C. lepida).
Scientists believe 14 species of tiger beetles live in Ontario, each one found in a specific habitat at a specific time of year. What sets them apart from most other beetle species is their pronotum – a section located above the base of the elytra – which is noticeably narrower than both the elytra and the head with its large, bulging eyes.
A tiger beetle is difficult to identify by its appearance, but its behaviour, location or the season will help disclose its identity. My recent experience with the seemingly playful beetle, on a sandy path along the East Don River, demonstrated one of this creature’s distinctive traits. Tiger beetles are incapable of maintaining a constant internal temperature, so they take advantage of ambient conditions. They bask in the sun to heat themselves, soaking up the necessary warmth to remain active for hunting later in the day. To avoid overheating, they raise themselves on their long legs, and this tiny elevation allows air to flow between the ground and the beetle, producing a cooling effect.
The game of beetle tag was also typical of this species. The beetle was not so much daring me to chase it as trying to see my position. Tiger beetles run so fast, they experience temporary blindness. They have to stop and reorient themselves to the location of predators and prey. Some beetle species can reach speeds of up to 2.5 metres per second, which is equivalent to over 100 times their body length per second. In comparison, the fastest human sprinter runs about six times his body length per second.
Despite their visual challenges, tiger beetles are skilled and fearsome hunters whose predatory methods are similar to those of their feline namesakes. These beetles quietly wait for ants, spiders and other ground-dwelling insects to appear, then pounce on the victim and devour it with their impressive mandibles. The strong, curved mouthparts of the adult tiger beetle have sharp edges for grasping and consuming prey. The feeding behaviour of the immature, or larval, beetle is just as efficient and deadly. The grubs live in vertical burrows underground. They wait at the top of the tunnel with their head level with the surface, grabbing insects that pass by. Hooks on the larva’s abdomen anchor it in place inside the burrow, ensuring its safety if a struggle with the prey ensues.
Most Ontario tiger beetles have a two-year life cycle. After spending the winter in an underground burrow, adults emerge in the spring to mate, lay eggs and then die. The female deposits her eggs underground, where they hatch and the larvae remain. Larvae go through three growth periods, known as instars. Prior to each instar moult, a larva will enlarge its burrow in preparation for an increase in its body size. Tiger beetle larvae usually complete two instars in the first year. They spend the winter and the following summer in their third instar and pupal phases. By late summer, the adults emerge. They overwinter underground and resurface the following spring.
My tiger beetle encounter was fortuitous. These are elusive creatures, and a person has to be in the right place at the right time to see one. In spring, a patch of sun on a forest path is the perfect place to await a six-spotted tiger beetle, which is common throughout Ontario, even in urban parks. Most other species, however, inhabit the sparse vegetation or sandy conditions of dunes, mud flats or alvars. Some stick to very specific locations within the province and are at serious risk from habitat alteration, such as the encroachment of non-native species. Some species are increasingly rare and their habitats threatened.
For example, the Laurentian tiger beetle (C. denikei), a striking and extremely rare tiger beetle, is limited to the western border of the province and Manitoulin Island. The hairy-necked tiger beetle (C. hirticollis) can be seen only on the shores of the Great Lakes and the Ottawa River. Lambton County, including Pinery Provincial Park on the southeast shore of Lake Huron, is the sole known habitat of the northern barrens tiger beetle (C. patruela), a remarkably beautiful insect whose status was classified as endangered in 2009.
The rare ghost tiger beetle, thought to exist only in Norfolk County and the Ottawa Valley, was found in 2004 in Northumberland County during field work by Todd Farrell, conservation biologist with the Nature Conservancy of Canada. The species sticks to sandy inland areas and currently inhabits a tract of ecologically significant land near Rice Lake as well as in Norfolk Sand Plain and the Ottawa area. These spectres were a welcome sight to Farrell. Although ghost tiger beetles are not endangered or threatened in Ontario yet, Farrell says the spread of invasive species such as knapweed and Scotch pine in the area and the disturbance of open sandy habitats threatens their continued survival.
Finding and documenting new populations of tiger beetles is vital to keeping them with us. They’re not economically significant species, nor are they pests – the two reasons why insects usually receive policy-makers’ attention. Nonetheless, these beetles are important parts of their ecosystems. As predators, they keep grasshopper, caterpillar and other insect populations in check; as prey, they provide food for dragonflies, frogs, birds and other small animals. Because tiger beetles require such specific habitat, they also serve as barometers of environmental health. As Tom Mason, curator of invertebrates and birds at the Toronto Zoo, points out, the disappearance of a habitat-specific species is a strong indication of ecological degradation.
Nature enthusiasts often participate in tracking butterflies and moths, but monitoring other insects tends to fall to the experts because many species are hard to identify, sometimes requiring a dissection to confirm their identity. No extensive entomological knowledge is needed to recognize tiger beetles, however. While the air is cold and snow covers the ground, they remain in their underground burrows awaiting the first signs of spring. Watch for them on warm April days. A tiny flash of green on a sunny forest path could be a tiger beetle challenging you to your own game of tag.
Jean Godawa teaches insect biology and ecology through workshops and lectures, focussing on the importance of these often-misunderstood yet vital creatures.
