The Great Butterworm Controversy

Within the reptile hobby in North America there are a few well established feeder insects. I mentioned most in an earlier post, but did not talk about butterworms. The reason I avoided butterworms is that, unfortunately, they are impossible to culture outside of Chile. More on that soon.

Butterworms, like all of the popular "worms" available as feeders, are actually the larval stage of an insect. In the case of butterworms the adult stage is the Chilean Moth, Chilecomadia moorei; they are also called the Trevo- and Tebro- worm (and even a few instances of Tebo- and Trebo), and are like silkworms in that they feed exclusively on a single species of tree, the Trevo/Tebro/Trebo/Tebo, Dasyphyllum diacanthoides.

C. moorei are exclusively found in Chile, and are considered a possibly invasive species. When shipped out of Chile, C. moorei larvae are irradiated to kill parasites, and, it is speculated, to prevent them from pupating. I have seen websites contradicting this, and claiming that the reason C. moorei larvae don't pupate in captivity is that they have a nearly 6 year larval stage, but this has come from only a few small, un-notable sources. For whatever reason C. moorei can't pupate outside of Chile, the fact keeps them a lucrative export for the country, frustrates hobbyists like myself, and prevents C. moorei  from becoming one of the premier feeder insects available.

On a reptile forum last month, a member posted a cautionary tale accompanied by gruesome pictures. Two of his Rhacodactylus geckos, a crested and a gargoyle, recently developed what appeared to be burns on their snouts after being fed butterworms. This spurred a small number of following posts claiming similar problems, including two which claimed the worms had melted plastic!

The story was reposted to the forum which I frequent (requires membership to view posts), and is being contested rather strongly by my fellow RC'ers. I myself was fairly critical of this originally, primarily because there is an overwhelming glut of information that states that these worms are not harmful, and only a few recent claims to the contrary. None the less, something burned those geckos, and something melted the plastic, and if we are to believe the sources of these complaints, there were no other possible causes.

So far speculation has ranged from absurd (radiation from export treatment! OH NO!) to plausible (crushing the heads before feeding them releases stomach acid that the worms use to burrow through wood, which otherwise would not be released until inside the geckos' stomachs, or that these are actually a cousin of C. moorei, C. valdiviana which feeds on more toxic eucalyptus. Not backing either of these theories, but both are more plausible than OMG RADIATION!!!!).

In an effort to nip this potential rumour in the butt, I have written to the author of one of my favourite blogs (and my favourite invertebrate blog), Arthropoda, requesting an investigation or resources for myself. Google can only get one so far.

So far I remain on the side of doubt. I have fed hundreds of butterworms to my reptiles, including hatchling leopard geckos, and I have never once seen anything close to resembling the reported burns. Then again, I have also never seen them melt plastic, which has been reported twice since the release of this story, and once on Arachnoboards last year. It will be interesting to see where this goes, and even better if it clears up the other rumours surrounding butterworms -such as their larval duration, export irradiation, and diet- in the process.


  1. I wouldn't want to feed my leopard gecko butter worms; being from Chile you don't know what they ate in the wild and in captivity. If they gut load a plant that is poisonous, that could affect the geckos/lizards.

    1. @FG
      Except you do know what they have eaten in the wild... the only food they eat is the trevo tree in Chile... clearly you haven't researched them much...

  2. A few things: I wanted to follow this with noting that I have now personally witnessed butterworms boring through plastic. On two separate occasions. Both times the larvae were left out at a high room temperature (~80F, in a breeding room), and the larvae was found dead, having half-eaten it's way through the bottom of a flimsy plastic container.
    Clearly, they have the ability to eat plastic, but I cannot verify that the ability is due to a caustic reaction.
    FG: Butterworms are a great feeder to add a bit of fat and calcium to your gecko's diet, and as Jondor noted, they don't eat anything once they've been taken from their food source. I have fed butterworms for years with no ill effects.
    Jondor, you're absolutely correct, but please be nicer. The internet is already full of jerks (and I've contributed myself enough, I just don't want to encourage mean things here).