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Acquired tastes - or why scorpions aren't as tasty as prawns

Updated Wednesday 5th August 2009

Dave Rothery asks what would we be prepared to eat to help save the planet?

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Flash-fried scorpions: Would you swap prawns for them? Copyrighted image Icon Copyright: BBC
Flash-fried scorpions: Would you swap your prawns for them?

There was an interesting item in programme two of Bang Goes the Theory. The story is that cows produce a lot of methane (which is a more potent greenhouse gas than carbon dioxide), but that insects make protein without releasing methane to the atmosphere. So, to do our bit towards saving the planet from global warming, why don’t we eat insects "and other creepy-crawlies" instead?

Presenter Liz then offers various insect delicacies to her three co-presenters, of which Dallas is at first reluctant to partake. Eventually, he concedes that he likes to eat prawns, and wonders why he is freaking out at the thought of eating something that Liz agrees is ‘essentially a prawn’. Was she right? Read on!

Why some foods revolt us is a complex issue. As I watched for the first time, I too was thinking "go on, I bet you’d eat a prawn, so why not a scorpion or a cricket?" - but that is not actually good logic when you look into it.

Insects and prawns may appear similar, but they are not very closely related. They both have segmented external skeletons and jointed limbs, placing them in the same Phylum (the Arthropoda), but they are in different divisions - Classes - of that Phylum. Insects constitute the Class Insecta, whereas prawns belong to the Class Crustacea.

The flash-fried scorpions that we see Liz cooking belong to a third arthropod Class, the Arachnida (of which spiders are familiar members), and are definitely not insects - despite any impression that the programme my leave to the contrary. Millipedes and centipedes form two other Classes of Arthropoda.

Turning to what non-vegetarians more familiarly eat - for example haddock, chickens and sheep - these belong to three different Classes of the Phylym Chordata. Thus a prawn, a scorpion and a locust are no more closely related to each other than a haddock is to a chicken and a sheep. No problem there, you might think. If you’d eat one, you’d probably eat the other.

Sea squirt - pass the ketchup? [image Open University, made available under a Creative Commons BY-NC-SA Licence]
Sea squirt - pass the ketchup?
[Image Open University, made available under a Creative Commons BY-NC-SA Licence]

But what about a frog, from the Class Amphibia, would you eat that? Or a sea squirt (Class Ascidiacea)? Both are Classes of the Phylum Chordata. The latter are probably eaten in China, but the majority of westerners would refuse them. Yet both are just as closely related to chickens as prawns are to scorpions, and as chickens are to sheep.

On the other hand, few westerners would eat dog, and I’m unaware of vulture being on the menu anywhere in the world, yet these are far more closely related to sheep and chickens than prawns are to scorpions. Then there are the molluscs; even people who love oysters or Coquille St Jacques (Phylum Mollusca, Class Bivalvia) would probably retch at the thought of eating slugs (Phylum Mollusca, Class Gastropoda).

My conclusions after all this are: One, scorpions aren’t insects; Two, what animals you are willing to eat has little to do with what they are related to.

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