Green Tiger Beetle (Cicindela campestris)
Life as a Borrower wouldn’t be easy – surface tension would turn raindrops deadly; temperature regulation would be a daily battle; and to top it all off there would be predators everywhere. Although many carnivorous invertebrates only predate particular species, it is incredibly likely that generalist hunters would happily incorporate a borrower into their varied diets.
Now imagine you are, in fact, a Borrower, and it’s a hot, dry, sunny day. You’ve been following the same dirt track for weeks, and you’re desperate for something to drink. Up ahead you spot a bright red wild strawberry – it’s as big as your head, and is more than enough to keep you going. But before you can take another step, you see something rocketing towards you at the speed of a Borrower-sized cheetah.
The beast freezes, perfectly poised, atop its six purple, bristly legs. Its huge eyes take in every miniscule motion, and its black, scythe-like jaws widen with anticipation. Suddenly, it launches past you and tackles a spider to the ground. Now, with its back to you, you can see its glistening, green elytra (wing-armour). There are a few cream spots dotted around its wing-case, and up close you can see the whole surface is covered in microscopic bumps, making its back sparkle in the sunlight. Before you can react, it launches into the air – its iridescent underside flashes blue, green, and red, as it soars across the path.
Tiger Beetles are fearsome predators, well deserving of their name – they are one some of our fastest land insects and will both run and fly in pursuit of prey. There are five Tiger Beetle species in the UK, but the Green Tiger Beetle is the most widespread and, well… green! Though the adult beetles will approach their quarry head-on, their larvae have a very different approach when it comes to securing a meal…
So, imagine you’re a Borrower again (sorry), and you’ve finally composed yourself after your encounter with the adult Tiger Beetle. You find yourself approaching a sandy patch by the path – although it’s uncomfortable, you move carefully across the coarse, grainy surface. A pale figure lurches from out of the ground in front of you, and you find yourself face to face with the Tiger Beetle Larva itself.
Despite facing you upside-down, on account of propelling itself backwards out of its deep tunnel, the larva is undeniably menacing. Its broad flat head and gaping mouth reaching up towards you; the other half of the larva, hidden beneath the ground, features a pair of protruding spines which allow the larva to firmly anchor itself in the tunnel – you wouldn’t have had much hope of escaping if you’d been caught in its ferocious mandibles.
Just to finish off, here are some fascinating Green Tiger Beetle facts:
- The markings on the elytra are concentrated near the end of the Tiger Beetle. This directs predators attacks away from the vital organs, and (owing to the incredible speed of the Green Tiger Beetle) means they are more likely to miss!
- Tiger Beetles hear using a kind of ear drum called a tympanum. The tympanum is located below the flight muscles, underneath the elytra. The only other beetles that hear in this way are Scarab Beetles, and their ear drum isn’t located in the same place, meaning they evolved ear drums independently of one another!
- The maximum speed of a Green Tiger Beetle ever recorded was 62cm per second – this may not sound like much, but when you’re only 1cm long in the first place that is quite a trot! They run so fast that they have to pause multiple times when in pursuit of prey, just to collect enough information to reorientate themselves (however in lab conditions with a ‘high-contrast’ dummy they can run at top speed non-stop)!
- Despite its incredible adaptations, the Green Tiger Beetle has plenty of predators, the most notable being the parasitoid wasp Methocha articulata. The wingless female intentionally attracts the attention of the larva, before paralysing the unsuspecting grub with her sting. She then drags the larva deep into the larva’s own tunnel and lays an egg on it, before covering the tunnel up again, so that her young wasp may hatch and feed on the Tiger Beetle larva in safety… Brutal! (this video shows a larva realising its been stung, and abandoning its tunnel in a last ditch attempt to escape the wasp: https://www.youtube.com/watch?v=zt2iZKqZx8Q)
This has been my first ever blog post – thank you so much for reading it! I hope it was enjoyable and informative, and I promise there won’t be as much ‘Borrower-abuse’ in the next one!
References and wider reading:
- https://www.ukbeetles.co.uk/ is an incredible resource for (you guessed it) UK beetles
- Pearson, D.L. (1988) Biology of Tiger Beetles. Annual Review of Entomology. 33, 123-147
- Kamoun, S. (1991) Parasematic Coloration: A Novel Anti-Predator Mechanism in Tiger Beetles (Coleoptera: Cicindelinae). The Coleopterists Bulletin. 45(1), 15-19
- Yager, D. (1995) Characterization of auditory afferents in the tiger beetle, Cicindela marutha Dow. Journal of Comparative Physiology A. 176(5), 587-599
- Forrest, T.G., Read, M.P., Farris, H.E., and Hoy, R.R. (1997) A tympanal hearing organ in scarab beetles. J Exp Biol.200(3), 601-606
- Gilbert, C. (1997) Visual control of cursorial prey pursuit by tiger beetles (Cicindelinae). Journal of Comparative Physiology A. 181(3), 217-230
- Wang, J. (2012) Closed loop visual guidance of prey pursuit by tiger beetles. Frontiers in Behavioural Neuroscience, 6
Will Pearce 