They're probably the best known celebration cakes around and retailers have been giving their caterpillars a spooky makeover for Halloween.
While M&S has turned its original Colin the Caterpillar into a 'Double Choc Yummy Mummy', Morrisons' has become Patch The Pumpkin.
As with the corgi cakes that both launched to celebrate the Queen's Platinum Jubilee, they're once again in high demand with shoppers eager to get their hands on one.
Read more: Morrisons accused of 'robbing shoppers' with eye-watering price of giant pumpkins
We're nothing if not thorough, so of course we had to try them out on your behalf.
First things first, how much are they?
Well the M&S one is £12 for 865g, whereas the Morrisons one costs £6.50 for 600g, so the latter works out the cheapest of the two.
Both are filled with chocolate buttercream and coated in chocolate. While Morrisons' Patch is decorated with white chocolate and sugar decorations, the M&S cake is coated with an extra layer of creamy white chocolate - hence the name 'Double Choc Yummy Mummy'.
So how do they rate?
It really depends on how much of a chocolate fan you are.
If, like me - and my children for that matter - you like as much chocolate as you can get, and wouldn't struggle to tackle a double layer of chocolate mixed with a thick buttercream filling, then the Yummy Mummy is for you.
If you prefer a more traditional swiss roll, with less of the filling and a thinner layer of chocolate, then the Morrisons one would be more your thing.
And while its brightly coloured sugar decorations make for a brighter centrepiece for your Halloween treat table, for us it wasn't a Patch on the double choc delight being served up by M&S. For us, Colin is king - and if you want a smaller version, you can get some little princes too, in the form of Yummy Mummy mini rolls.
Both can be bought in store, or online, with M&S food orders delivered via Ocado.
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