The Green Tiger beetle
The Green tiger beetle, Cicindela campestris, is a beautiful looking, strikingly iridescent, green beetle about 1 to 1.5cm long with yellow spots on its wing cases and large eyes and mandibles which belie the fact that they are superb predators with massive appetites.
Their scientific name originated from the Latin word cicindela, meaning ‘glowworm’ which comes from the fact that members of the genus are metallic in appearance and seem to flash in the sun, and campestris, from the Latin for ‘field’, or ‘plateau’, as they are often seen on flat, open stretches of ground.
They are commonly spotted running across tracks on moorland or in forestry in the daytime as they are diurnal (daytime) insects with very keen eyesight and prey on other diurnal invertebrates, including other species of beetles, which they chase down until they get exhausted, and then seize in their razor sharp jaws. They are also ambush predators and will often wait on top of burrows, including those of spiders, so it can surprise prey when it emerges.
Too fast to focus
When they are in pursuit of prey Tiger beetles are dogged and tenacious and extremely fast, but entomologists, (the name for those who study insects), have long noticed that tiger beetles tend to stop and start when they are in the middle of a chase. For a long while the reason for this was a mystery but recent research has shown that they do this precisely because they are too fast to focus on their prey! Cole Gilbert, professor of entomology at Cornell university explains exactly how;
"If the tiger beetles move too quickly, they don't gather enough photons (illumination into the beetle's eyes) to form an image of their prey,",
“Now, it doesn't mean they are not receptive. It just means that at their speed during the chase, they're not getting enough photons reflected from the prey to make an image and locate the prey. That is why they have to stop, look around and go. Although it is temporary, they go blind."
Cornell researchers also discovered that, unlike most insects that wave their ‘feelers’ around to sense their environs, Tiger beetles will hold their antennae out rigidly in front of them to sense their environments, this is to avoid obstacles while running fast and they are very fast indeed; as a comparison the runner Usain Bolt covers 5 of his body lengths in one second, but a Tiger beetle covers 120 in the same amount of time, sprinting at up to 5mph, which is impressive for something that’s only 1 and a half centimetres long!
The Green Tiger beetle also has another trick up its chitinous sleeve, in that it can fly. If disturbed they can make fast, buzzing flights, of up to 20 or 30ft, clattering away in a manner which can be very surprising when you hadn’t noticed it was there or or if you were chasing it in the hope of taking a photograph! When they land, (and this has made me reckon that some insects are a lot more intelligent than we give them credit for) instead of carrying on running for shelter, they turn around straight away to stare at you and figure out what your next move is going to be.
Aggressive larvae
In its larval stage, the Green Tiger beetle is just as aggressive and wick as when grown up, and they have a unique way of hunting. The carnivorous grub digs a vertical tunnel and braces itself, using a hooked hump on its back, against the walls, its flat face flush with the surface of the ground.
What appears to be its face, however, is actually a combination of the head and a ‘thoracic plate’ on its back, and the larvae stays in a hunched position in the burrow with the head and this thoracic plate together exactly filling the top of the burrow just like a spring loaded manhole cover. The slightest disturbance by a predator will make it disappear instantaneously, too fast for you to see, but if it senses prey it darts out, and can even be ‘fished’ for, as can be seen in this video of a related species, Cicindela aurulenta, where it pounces, lightning quick, to grab passing, unsuspecting, insects and drag them into the burrow to meet their grisly doom.
These tunnels start out narrow, but as it grows the grub gradually widens and extends its hidy-hole until it eventually reaches the width of a pencil, the fastidious grub will keep the area immediately around the lip of this tunnel clean of debris. When the grub is using it for hunting, the burrow may only be a few inches deep, but as Green Tiger beetles overwinter as grubs, the hole will be extended below the frost line in winter.
Even the hunters are hunted
Although the Green tiger beetle might seem like an apex predator in the insect world it is in fact preyed upon itself, as the larvae are parasitized by a species of solitary wasp; Methoca articulata. These wasps lay their eggs inside the body of the Green tiger beetle’s larvae, with the female wasp being smooth and slender shaped in order to survive being gripped by the larvae’s strong mandibles.
The wasp actively seeks out Tiger beetle burrows and allows itself to be caught and dragged inside the burrow and then stings the Green tiger beetle larvae to paralyse it, when it is safely subdued she then deposits an egg into the larvae’s burrow and escapes. When this egg hatches, the wasp larva can feed off the beetle larva in the safety of its own burrow.
You would never suspect, walking along a fellside track, that such dramas could be occurring under your very feet, but this goes to prove that sometimes its well worth your time to lie down in the heather and watch what’s going on in worlds which are so small, that we don’t normally pay them any attention.
[link] [comments]
source https://www.reddit.com/r/Entomology/comments/nrmv8z/out_walking_on_the_fells_yesterday_i_spotted_a/
No comments:
Post a Comment