Bombardier Beetle-Dan Ryan

Chemical Spray:

The main interesting feature of this beetle is its explosive defense system, demonstrated above. This is what separates the beetle from the rest. The bombardier beetle when threatened can spray a burning caustic liquid from the rear of the abdomen. The liquid can reach an astonishing 22 miles per hour and can be at temperatures that reach close to 100 degrees Celsius. The way that this chemical reaction does not simply kill the beetle is due to the fact that the beetle has two chambers in the abdomen. One chamber contains hydrogen peroxide and hydroquinones, these two liquids combined are barely stable and in fact they can be dangerous just by themselves. The other chamber contains enzymes like peroxidases and catalase. These two enzymes are enough to set off the reaction and allows for such a violent reaction to take place.

The chemical reaction is as follows

So once the beetle is threatened it opens the valve and contracts the muscular walls of the two chambers that contain both substances. The chambers empty into a reaction chamber that is sealed off by the pressure of the reaction itself allowing for the protection of the beetles internal organs. This reaction produces a lot of heat meaning the beetle has to find a way to deal with the heat, though that’s another feature that will be talked about later. Finally the beetle fires the liquid at whatever is threatening it at a rate between 385 to 735 pulses a second. This spray pattern is extremely important due to the fact if it was a constant stream the beetle would be injuring itself every time it sprayed the chemicals due to the fact that the pressure would not be enough to get the spray away from the beetles’ body, thus singeing itself every time the chemicals were released.

Armor:

The second interesting feature is the specific armor that the beetle has to develop to deal with the chemical reaction it uses as a defense system. The beetle rear abdomen where the two chemical chambers are housed are reinforced with extra layers of extremely study material like chitin and waxes that beetle produces to be able to withstand the explosive reaction that it produces within itself. This armor also is used to do the pulse mechanic that the beetle uses to expel its chemical. This is super unique because the beetle didn’t evolve a separate muscle to spray the chemicals allowing the beetle to send the chemical out passively. This is extremely important because this means the beetle doesn’t have to control the reaction in anyway and it takes less energy to do this self-defense technique. It also provides human research into the potential of armor that can resist explosions better in fact there have been prototypes of armor that have been based off these structures already being tested, along with other animals such as oysters and armor that resembles fish scales.

Controversy:

These bugs aren’t just being looked at due to their defensive mechanism; rather they are one of the main arguments between scientists as well. There seems to be a lot of speculation on whether these beetles should belong to the Carabidae family. This is mostly due to the argument trying to determine if the beetle truly evolved from beetles or if they became part of the beetle group separately meaning they should be part of their own family. This is due to the fact that many scientists don’t believe that beetles would never naturally evolve the defense system that is the defining characteristic of the species. This is due to the fact that ancestors of this beetle would have many unnecessary parts while this extremely complex defense system was being “mad” that there fitness would suffer. This is the hypothesis held by many scientist, and with no ancestor being seen in the group they are up for a lot of speculation. The other side of this argument is stating that the system is so complex that it would be almost impossible for the beetle to just pop up out of nowhere. Until an ancestor of this unique beetle shows up this argument will likely never be resolved.

Resources:

"Dean.; et al. (1990). "Defensive Spray of the Bombardier Beetle: A Biological Pulse Jet". Science Magazine.

Arndt, Moore, Lee & Ortiz. 2015. Mechanistic origins of bombardier beetle (Brachinini) explosion-induced defensive spray pulsation. Science http://dx.doi.org/10.1126/science.1261166

"Aneshansley.; et al. (1969). "Biochemistry at 100 C: Explosive Secretory Discharge of Bombardier Beetles (Brachinus)". Science Magazine.

Eisner, T; Aneshansley, D. J.; Eisner, M.; Attygalle, A. B.; Alsop, D. W.; Meinwald, J. (2000). "Spray mechanism of the most primitive bombardier beetle (Metrius contractus)". Journal of Experimental Biology 203 (8): 1265–1275.