Feeding earthworms to garter snakes is complicated by the fact that there are, broadly speaking, two kinds of earthworms, only one of which is safe to use.
Red wigglers (Eisenia foetida) are the worms used in vermicomposting, so they’re plentiful and easy to raise in captivity. But if the prospect of a limitless supply of worms fed on garbage scraps sounds too good to be true, it is. You can’t use them.
People are disappointed to hear this, and they ask why, particularly since they may have used red wigglers without incident as food for aquatic turtles (as one friend told me), or have managed to feed them to snakes without any problems.
This is compounded by the unclear advice given by pet manuals, many of which simply don’t make a distinction between red wigglers and other worms. Perlowin (2005) simply says they taste bad: “[A]void red worms (also called dung worms), which are particularly foul tasting to these snakes” (p. 38).1 Neil Ford (in Rossman, Ford and Seigel, 1996), on the other hand, says they’re a bit more than yucky: “Some bait worms (Eisenia, sold as ‘red wigglers’) are toxic” (p. 121).
Whether they’re reported to be toxic or simply taste bad, red wigglers, it seems, ought to be avoided. But understanding why is important: advice won’t necessarily be followed if it isn’t backed up with some evidence. Fortunately, some anecdotal evidence does exist.
I can attest to the toxicity [of red wigglers] — I saw its effects myself on a pretty large scale in about 1989.
I was told by our lab manager (an excellent herpetoculturist and published biologist herself) that she did find documentation (seconded by our vet at the time, also published in reptile veterinary work) that Eisenia species (compost worms, red wigglers) can produce coelomic fluids toxic to snakes (and I’m sure other creatures). It appears to be derived from their diet, but we never isolated how — we actually raised our own for some time, but gave up on pursuing this since it was just too risky and there were safe worm food sources available (any Lumbricoid “leaf worms” are small versions of nightcrawlers that are just right for smaller snakes, and most of the soil worms you’ll find are relatives).
I don’t really want to remember the dozens of baby snakes that literally puked themselves to death on just one meal of toxic worms … even though we’d had many safe meals, not knowing what caused the one batch (same supplier, same packaged diet) to be so much more toxic, we didn’t want to risk it happening again.
So red wigglers’ toxicity may depend on their diet. If so, unless you can control their diet and know exactly what in that diet can cause toxicity, you’re better off using other worms. If not, you’re better off using other worms in any event.
As Lani mentioned in her message, the worms you do want to use are nightcrawlers (Lumbricus terrestris) and related species, whether they’re known as leaf worms, dew worms or garden worms. These are the earthworms you see on the sidewalk when it rains, the earthworms you dig up in your garden, and the nightcrawlers you buy from the bait shop. (Note, though, that red wigglers may occasionally be sold as trout bait.)
Though these worms are much safer to use as food, they’re a lot harder to keep. For one thing, they seem to be next to impossible to cultivate: all the worms offered for sale are collected from the wild — more problematically, many of them are reportedly collected from golf course lawns, which means they may well be chock-full of pesticides. And they thrive on lower temperatures: you need to keep them in the refrigerator.
Supply is another issue: nightcrawlers are harder to get. You can buy red wigglers by the pound, but where I live, nightcrawlers are sold by the dozen (they cost $2.75 per dozen around here). And those sold by bait stores are invariably very large: too large for small garter snakes, especially since large nightcrawlers are muscular enough to crawl back out of the mouths of garter snakes as long as 40 or 50 cm. Smaller worms must be collected from gardens, sidewalks or roads — but, in the case of sidewalks and roads, environmental pollution is a real issue. And collecting requires sustained effort: even a single snake can eat a lot of worms; they’re not nearly as nutritious (or as filling) as vertebrate prey.
Finally, it’s worth pointing out that even nightcrawlers can be vectors for internal parasites. There is always a risk in using earthworms as garter snake food; some worms are simply much riskier than others.
- Perlowin also says to “[o]ffer common earthworms rather than night crawlers [sic],” a distinction I find quite baffling. Nor does he explain why nightcrawlers should be avoided.