The Bombardier beetle part 3 - the defence effectiveness

If we look at one of the smaller bombardier beetle species, the Brachinus crepitans, which is no larger than 1 cm, and place it between the fingers you will just be able to hear the boom and see the vapour cloud, but only barely. If you place it between your lips, you will be able to feel the explosion as an uncomfortable burning sensation, not the strongest defence. But the more tropical species can become quite large and have a stronger defence to the point where it can burn and cauterize the skin. Humans aren’t the bombardier beetle’s natural enemy and if we stay with the species Brachinus crepitans, and its closest relatives, the enemies consist mainly of other beetles, ants, and spiders, even though frogs and reptiles can go after them.

When looking at the effectiveness of its chemical defence, we could use the ant as an example as in the video. If an ant bites the bombardier beetle, it will be sprayed with burning hot quinone. When the ant has been hit, it will make a retreat, when a series of seizures will commence. Each seizure will last only for a few seconds. If the ant gets more than 20 seizures it will be incapacitated for a couple of minutes.

Even against larger enemies, such as other beetles and spiders, is the defence quite effective. The effectiveness of the defence doesn’t stop at spiders. If a frog happens to catch a bombardier beetle, it will immediately spit it out as soon as the hot gas and liquid is released into its mouth. Because a small portion of the bombardier beetle’s abdomen isn’t covered by the elytra, it is capable of aiming its explosions in multiple directions.

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There is no doubt that the beetle’s defensive mechanism is highly effective and able to pacify many assailants long enough for the beetle to make a quick getaway. Not only is the bombardier beetle’s defence effective on its own, but bombardier beetles tend to get together in groups and can easily be up to a hundred individuals under a single rock. With the beetles’ effective defence and large number it will make it a hell for anyone attacking or disturbing them.

It might sound as if the bombardier beetle is invincible, but some animals have developed methods to counteract the beetle’s defence. One of these animals is the spiders of the genus Argiope. These spiders carefully wrap the bombardier beetle’s abdomen in its silk thread. When the beetle discovers what is going on and ploy its defence it will be too late. The beetle will by then be spun into the threads and won’t be able to aim its spray at the spider, which weakens the effectiveness. Should the beetle succeed in hitting the spider and pacify it, the spider will simply return later and put an end to the beetle’s life (Jørum, 1998).

Part 1 – the chemical defence

Part 2 – the enzymes

Sources in part 1

2

Asian Multi-spotted Ladybird Beetle (Harmonia axyridis):

The first photo set shows the variety in coloration and spotting, bit what stays the same are the large white edge spots on the sides of the pronotum (thoracic shield).  (photo by ©entomart)

The second set shows the full life cycle of H. axyridis. (photo by puddingforbrains).

This species has been widely introduced, purposefully, into Europe and North America, as garden pest control. This has had a deleterious effect on several of our native lady bird beetle (“ladybugs”) species, as native species are often unable to compete with the voracious predator of scales and aphids.

In the United States, we do have several species of native Ladybird Beetle. Find out more here:

http://bugguide.net/node/view/179

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