Fast & Furious: The Agile World of Tiger Beetles

 

Figure 1. Six-spotted tiger beetle (Cicindela sexguttata)

 

Imagine an insect smaller than your thumb that if it was the size of a human, could completely outrun a cheetah. With long, tall legs built for speed, menacing mandibles able to bite through tough exoskeleton, and iridescent armor gleaming brightly in the sun, the tiger beetle is a striking predator. Because they move so fast, and their resemblance to some flies, one could easily pass it off for something else. But if you can get a snapshot of these speed demons, they are fascinating.

 

The tiger beetles make up a family of insects called Cicindelidae, being closely related to other predaceous beetles such as Carabidae. These both fall under the suborder Adephaga, along with some other families. Approximately 2600 species have been discovered so far, and are found almost all over the world, except for some inhospitable places such as Antarctica, the Arctic, and isolated islands such as Hawaii and the Maldives. They are most easily found in open or sandy environments with lots of sunlight, deserts, and sandy beaches, but can also be found in other environments on the ground, such as hardwood forest floors [1, 2]. If you do find one and want to get a closer look, you must do so with stealth and caution. You will quickly realize how hard they are to catch, as they will be able to dart away (or sometimes fly) far out of reach at the slightest indication of danger. The fastest of these beetles can reach running speeds of up to 5.5 miles per hour, covering a staggering 120 body lengths in one second. This would be the equivalent of an olympic sprinter running at 480 miles per hour [3]! In fact, tiger beetles move so fast that despite their relatively excellent vision for an insect, they cannot see their prey while moving to chase it down, and must stop to see it again before attacking [3]. They catch and eat the small insects they overwhelm with their sheer speed by grabbing them with their long, sharp mandibles.

 

 

Figure 2. Color variations in Cicindelidia politula

Figure 2. Color variations in Cicindelidia politula

 

If you are able to sneak up on one for a closer look, the colors will definitely catch your eye.

Tiger beetles exhibit beautiful color variations. For example, the six-spotted tiger beetle (Cicindela sexguttata) is a vibrant iridescent green that can show off blue hues as well under different lighting (Figure 1). True to its name, it typically has six small white spots on its elytra (the hardened forewings). These spots are usually arranged in three pairs along the length of each elytron. Other species can have many colors such as black, blue, red, and brown, such as the Limestone Tiger Beetle (Cicindelidia politula) (Figure 2).

 

 

Figure 3. Japanese tiger beetle (Cicindela chinensis japonica)

Figure 3. Japanese tiger beetle (Cicindela chinensis japonica)

 

Sometimes they can even have a rainbow of iridescence, as in the case of the Japanese tiger beetle (Cicindela chinensis japonica) (Figure 3), which almost resembles the appearance of a heat map with its collection of colors. Why might these beetles be so colorful and iridescent, even where they do not seem to blend in? Even if it could be for intraspecific communication, would the bright colors not attract predators? It has been noted that some of these beetles produce toxins such as benzaldehyde as a defense mechanism, so these colors could act as a signal to deter these predators from a distasteful meal [4]. But even beyond this, iridescence in beetles has been shown to possibly deter predators even against contrasting backgrounds [5]. Sometimes it helps to be bright and colorful! Or perhaps God just decided to have a little fun with his paintbrush.

 

 

Figure 4. Tiger beetle larva and tunnel

 

Tiger beetles have a life cycle of complete metamorphosis. After mating, the female lays individual eggs into the ground that she deems suitable for the larvae to live in, covering the hole to disguise it from possible predators. The larvae have a very different hunting method compared to the adults, using a sit-and-wait strategy. They create burrows with little openings to live in, and when a prey item such as an ant walks by the opening, they pop out part of their body at lightning speed to grab it, and pull it into the burrow to digest and eat it (Figure 4) [1, 2]. The larvae go through three stages of growth, called instars. The final instar modifies its burrow to make space to turn into a pupa. In this form, the adult structures form and eventually develop, until the adult emerges to repeat the cycle. This life cycle is usually two years in most species, but some do it in one, while others can take three or more [1]. The characteristic of complete metamorphosis greatly aids in the success of many insect species that use it in resource partitioning, and is one reason why they are the most successful class of animals. As has been shown, tiger beetles have adapted to have great success in their ecological niches they fulfill. If one can catch a glimpse of these speedy and flashy predators, they might just discover something beautiful and fascinating in its purpose and form, and one more reason to worship their Creator.

 

 

 

Sources:

1. Pearson, David L., et al. Field Guide to the Tiger Beetles of the United States and Canada: Identification, Natural History, and Distribution of the Cicindelidae. Oxford University Press, 2005.

2. Borror, Donald Joyce, et al. An Introduction to the Study of Insects. 5th ed, Saunders College Pub, 1981.
3. The Tiger Beetle Is Incredibly Fast for Its Size. Directed by Smithsonian Channel, 2020. YouTube, 

 https://www.youtube.com/watch?v=xZIrY7VZaNA.

4. Tiger Beetles: Fierce Hunters, Fast Movers. Directed by Florida Museum, 2019. YouTube, 

 https://www.youtube.com/watch?v=E3kVF3pWk80.

5. Kjernsmo, Karin, et al. “Beetle Iridescence Induces an Avoidance Response in Naïve Avian Predators.” Animal Behaviour, vol. 188, June 2022, pp. 45–50. ScienceDirect, 

 https://doi.org/10.1016/j.anbehav.2022.04.005.

 

Images:

Figure 1: https://commons.wikimedia.org/wiki/File:Six-spotted_Tiger_Beetle_%2848343587641%29.jpg
Figure 2: 

https://www.mdpi.com/2073-4425/11/3/265 extracted from Duran, D. P., Laroche, R. A., Gough, H. M., Gwiazdowski, R. A., Knisley, C. B., Herrmann, D. P., Roman, S. J., & Egan, S. P. (2020). Geographic Life History Differences Predict Genomic Divergence Better than Mitochondrial Barcodes or Phenotype. Genes, 11(3), Article 3. https://doi.org/10.3390/genes11030265

Figure 3: 

https://commons.wikimedia.org/wiki/File:Cicindela_chinensis_japonica_0s3.JPG 

Figure 4: https://entomology.ces.ncsu.edu/biological-control-information-center/beneficial-predators/tiger-beetle/