These beetles can blast boiling acid! (Bombardier beetles)

This week we look at a group of beetles that are well known for their abilities to produce and shoot boiling acid from their abdomen! 

 

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Transcription: 

 

Welcome to Episode 56 of Insects for Fun! The weekly podcast covering all things entomology, and creepy crawlies. Today we are taking a look into a beetle that packs some crazy firepower in the form of boiling acid. 

 

Bombardier beetles are a group of ground dwelling beetles in the family carabidae. There are over 500 species known and can be found on every continent except for that one dark, and cold special place… Antarctica. I had to say it this time cause I have no idea if there are new listeners on this episode. But yeah these beetles are pretty much everywhere on earth and inhabit woodlands, grasslands, and even deserts! Don’t expect them to be all over arid climates though. The fact is these guys need moisture for their eggs, and they prefer an area that can provide cover during the day and water. Many are commonly found near lakes, ponds, and rivers. 

 

As for their appearance, the beetles come in a variety of colors and sizes, but the body shape is relatively similar. For example I can be pretty sure a beetle is a bombardier if the head and thorax are narrow compared to the abdomen, and the shape is similar to an upside down maraca (maraca noise). The abdomens have to be larger than everything else because this is where they store their special chemicals, but we’ll get into that jazz later.

 

In the United States there are 40 species and these all surprisingly look pretty similar. Orange/reddish bodies with their elytra being greenish blue or navy. Elytra is the term we use for the hard shells beetles have over their wings by the way. Honestly, some of the US species are incredibly stunning and I’ll have the photos as usual on the Instagram page. The average size for these guys is quite small with many people often referring to them as the size of a fingernail given you don’t have hulk hands or something. (insert angry hulk noise) 

 

Bombardier beetles begin their life as an egg in the soil, and chow down on smaller insect larvae until they reach adulthood. Some bombardier beetles will actually lay their eggs in the carcass of a dead animal because it serves as protection and a food magnet for other smaller insect larvae like maggots. The beetles go through a series of molts during the summer months until fall and then emerge from the ground in spring as an adult. Most of us would never know whether or not there are bombardier larvae around because they spend all their life buried in decaying matter feeding on other ground-dwelling animals like grubs and worms or even the decaying matter itself depending on what it is. The adult beetles are also carnivorous, but they don’t actually seek out lively prey. Instead, they patrol at night looking for weakened insects for young larvae to feed on, and once the sun begins to rise they seek shelter somewhere away from the heat and away from the eyes of potential predators like frogs and toads. The beetles prefer a solitary life during the night, but what’s interesting is that during the day they’ll hide with others, and it's been found that they don’t discriminate. Bombardier beetles actively seek out places with other bombardier beetles, regardless of the species and stay huddled together during the day. 

 

Something else which is interesting to note is that these beetles don’t use their acid spray to hunt. It’s a defense mechanism used only when encountered with a threat like a toad or frog, and yeah it does kinda seem like the only things crazy enough to try and eat one of these are toads and frogs. They also aren’t very successful at it either with around 40% of the beetles getting thrown up and walking away after the whole ordeal. 

 

So how exactly do bombardier beetles manage to create such a powerful weapon, and why aren’t they getting boiled from the inside out? As I mentioned earlier these guys have a large abdomen, and the reason is because they store two separate liquid compounds which cannot come in contact with each other until the moment of release. These compounds would be Hydrogen peroxide, and Hydroquinone. When the beetle is threatened or under attack these two liquids get released through opened valves into a special chamber at the very back of their abdomen. This special chamber holds the third ingredient required for such an explosion, a special enzyme which creates the reaction allowing the bombardier beetles to shoot out near boiling acid at incredible speeds. This acid is known as benzoquinone, and upon release reaches 100 degrees C. The beetles are known to release up to 500 micro explosions in a second, and can fire their acid canons up to 20 times before depletions. Afterwards, it can take up to 24 hours to fully recharge and the beetles caught by frogs during this recharge time have no chance of escape. This is of course where they get the name Bombardier as well, because if you didn’t know a bombardier is a person who is responsible for aiming and releasing bombs from an aerial craft. And just like the people, some bombardier beetles can aim their weapons with incredible accuracy. For example one species in Africa known as Stenaptinus insignus can rotate its abdomen 270 degrees in a swivel-like motion. 

 

Many of you are probably wondering now what happens if we get hit by this crazy spray, and the answer is a painful and memorable experience (insert sound). You won’t be severely injured or anything like that. In fact Charles Darwin actually wrote about an experience when a bombardier beetle sprayed him in the mouth! He was in the UK collecting beetles during undergrad, and got a bit too greedy. You see Darwin already had his hands full of two different carabidae beetles when he came across an incredibly rare beetle in the UK known as Panagaeus cruxmajor. Darwin did not want to lose any of his captures so he put one of the carabidae in between his teeth to free a hand. This of course was a massive mistake which resulted in him losing all three, but as we know Darwin survived this ordeal and didn’t lose anything other than what he was trying to collect that day. I have no idea why he chose his mouth of all places, did he not have pockets? What was he even doing collecting insects without a jar? Unfortunately, we’ll never get to ask him these questions. But at least he left a written tale. 

 

This concludes today’s episode! As always I hope you enjoyed it and if you are enjoying the podcast it would help me and the show a huge amount if you gave it a rating and review! These really do go a long way in boosting the show's visibility. If you want more insects for fun you can support the show on Patreon.com/insects for fun where you can get bonus episodes and vlogs as well as polls for future episodes! Links to everything will be available in the episode notes. Also! I’ve been working on the merch, and I would like your input for what kinds of items you want! So far I’ve designed a T-shirt and a Hoodie which will be available in multiple colors. If you’re a Spotify listener you can directly send me a message at the bottom of this episode on your listening app. For everyone else, you can DM me on Instagram, FB, or send me an email. Links to all the socials as always are in the show notes.