Insectile rocketry in action
Imagine that you’re a predator lunging for a tasty looking beetle, and just as you get close to chomping it you receive a blast of hundred degree Celsius steam mixed with nasty chemicals accompanied by aloud blast…Instant deiscomfort! It’s a common scenario, since some 500 species of bombardier beetle contain what effectively amounts to a biological rocket powered internal combustion engine inside them.
In their abdomen they have a reaction chamber, where hydrogen peroxide and hydroquinone meet from their separate storage tanks. Here they react with water and enzymes (proteins that catalyse other reactions, ie speed up their rate), heat up close to water’s boiling point (which the insect somehow survives) and explode out of an aimable cannon at their rear ends. Fatal to other insects and small creatures, they are even quite painful to humans should you be so unlucky as to encounter one.
Their chemical defence mechanism depends on feedback loops, when the muscle is contracted to open the valves of the storage tanks and the reaction starts, the resulting pressure closes the valves when it reaches the suitable level for firing before activating an outlet valve and firing out in some 70 pulses (to avoid harm to the beetle), all in a fraction of a second. Some have to present their backsides to the enemy, but others have highly accurate steerable barrels with a range of 270 degrees that also aim through the legs and are ableto regulate the spray. They are good for about 20 shots before needing to recharge, when the beetle has run out of ammo it generates new supplies of chemicals metabolically. A similar chemical propulsion system was used in the German V1 ‘doodlebug’ rockets during the second world war.
One of them supposedly spat into Darwin’s mouth during his Beagle journey, his hands already full of other new and unique specimens and not enough jars around. All three beetles escaped. They are found on every continent barring Antarctica, usually in temperate wood and grass lands. Most are carnivorous night hunters, though they only use their guns in self defence. There are many variants on the chemistry across the family, but the basic principle is the same, rocket wielding insects.
In the research described here, scientists observed how toads responded after eating the beetles and receiving a dose of internal rocketry, and surprisingly enough they vomited half of them out undigested within a short period of time (ranging from a dozen minutes to 107), proving that the strategy is effective often enough to be worth it in evolutionary terms. Toad vomiting is a slow process in case you wondered, as it involves turning the entire stomach inside out rather than just contracting muscles around it. The most successful escapes happened when small toads swallowed larger beetles, for obvious reasons. As a control the team also fed beetles to toads after disabling their rockets by repeated triggering, and only 5% of these came back up. No one knows how one survived nearly 2 hours in the toad’s stomach, and the team wonder is the chemicals involved in the rocket might also neutralise stomach acids and enzymes somehow.
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Image credit: S. Sugiura
A video: https://youtu.be/54h1I9ykq8k
General info on Bombardier beetles:
A video of one firing: https://www.youtube.com/watch?feature=player_embedded&v=Pib9qT-pccI
Original paper, free access: http://bit.ly/2ETSot7