How hungry are caterpillars anyway?

Proving once and for all that great minds think alike, Christie Bahlai and I share some concerns about the Carle book, a.k.a. The Very Hungry Caterpillar:

So how hungry are caterpillars anyway? It’s surprisingly easy to find out, and it’s a good illustration of what we can do with open data. In this post, I’ll use data from the GLOBI database @poel14, to see which of the species from the genus Pieris is the very-hungriest. Because, clearly, the appropriate response to people cracking jokes at children’s books is to design a data-analysis plan.

The GLOBI database (it stands for Global Biotic Interactions) lists data from the literature, and we can access it from R using rglobi. So before you start:

install.packages("rglobi")
library(rglobi)

Once this is done, we can look for all interactions that have Pieris eating something:

pieris_interactions <- get_interactions("Pieris", interaction.type="eats")

This gives (as of the writing of this post), 232 interactions. Looking good! Now, we can build an incidence table of what Pieris species is eating what food source. The output of get_interactions has columns for the source and target taxa, so this is fairly easy:

A <- table(pieris_interactions$source_taxon_name, pieris_interactions$target_taxon_name)

This table has 14 rows (for 14 Pieris species), and 137 food items. To know which is very-hungriest of all, we can simply sum the rows:

generality <- rowSums(A)
sort(rowSums(A))

Here is the result:

Pieris species Number of known items in diet
rapae 91
brassicae 55
napi 51
canidia 10
virginiensis 6
marginalis 4
krueperi 3
brassicoides 3
naganum 2
manii 2
ergane 2
melete 1
deota 1
cheiranthi 1

OK, so that settles it. Pieris rapae IS a very hungry caterpillar.

But more seriously, isn’t that amazing? That the integration of open data and open software means that we can now go and test hypotheses with very few effort? I can’t help but feel that we are extremely lucky to have all of these resources available. And I’m working on a paper that will showcase a more ambitious example. Open data are good. Use them.

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