We recently received a question from a reader about the “horrible stinking odor” her dogs bring into the house after digging around in dirt that contains a worm, caterpillar, or millipede. (The reader technically wrote that she found a “worm/caterpillar/millipede,” so we went ahead and assumed this means that she found one of these creatures, as opposed to a chimerical hybrid of all three creatures.) Even after the reader washes her dogs, the bad smell of the worm (or caterpillar or millipede) doesn’t go away. However, after two hours, regardless of whether the dogs have been washed, the unpleasant odor is gone. The reader wasn’t really concerned about the smell, however; she only wanted to know if her dogs were in danger. So, the rather specific question before us is this: are foul-smelling worms, millipedes, or caterpillars harmful to dogs?
Although the reader wasn’t directly concerned with identifying the source of the odor, this is obviously a relevant part of answering her question. If we can determine what she is finding, a lot of information flows from this. However, the reader didn’t give us many details to work with. We know that the creature in question smells bad and that it was found in the dirt, and these two observations lead us in different directions.
The fact that the creatures were found in the dirt suggests that our reader found some sort of earthworm. Because their bodies can dry out so quickly, earthworms spend most of their time in moist environments like soil. A couple of dogs digging in the soil could certainly turn up an earthworm or two, but we aren’t sure why a dog who unearths a couple of earthworms would smell bad as a result. Earthworms don’t really have any distinct smell, at least in our experience. A large concentration of worms that have been dead for a while can smell bad (evidently compost operations with dead worms can smell like dead fish), but this isn’t really applicable to our reader’s situation. So, our reader doesn’t appear to be dealing with the most likely creature to find when digging in the soil, an earthworm, and even if she is, her dogs shouldn’t be harmed by whatever smell an earthworm, dead or alive, can transmit to a dog.
The reader also mentioned caterpillars and millipedes, and both of these suggestions are more consistent with the foul-smelling nature of whatever our reader found. (They could also be found on the ground, and perhaps even slightly under the top layer, at least in the case of millipedes.) When threatened, caterpillars and millipedes will emit a malodorous substance that is designed to deter predators from attacking. Millipedes, who don’t bite or sting, are especially known for this tactic, as we explain in our article about why millipedes smell bad. Sometimes these secretions not only smell bad, but are also harmful. However, the chemicals are generally only harmful for the creature’s natural predators – they might be able to eat through another insect’s exoskeleton, for instance – and of course dogs are not the natural predators of caterpillars and millipedes, nor do they have exoskeletons, so they shouldn’t be seriously harmed by whatever the caterpillar or millipede emits. Perhaps some skin irritation is possible, and this is obviously worth monitoring, but in general these chemical defenses simply smell bad.
So, to sum everything up, we suspect our reader’s dogs have run into some type of caterpillar or millipede that, when threatened by the dogs digging, activated a defense mechanism that involves the secretion of chemicals that smell bad. These chemicals shouldn’t cause any harm to the dogs, although if the reader notices anything wrong with her dogs, she should of course take them to the vet. (We are not in any way providing medical advice for our reader’s dogs. We are merely pointing out what seems to follow from what we know about worms, caterpillars, and millipedes. Moreover, it is not as if we know the exact chemical properties of every millipede or caterpillar secretion. It is impossible to know how our reader’s dog might react to any given chemical.) As for why the offensive odor is only temporary, it is hard to say, although it is worth noting that foul smells tend to dissipate over time, and a defense mechanism that relies on an odor wouldn’t necessarily need to be long-acting. A couple of hours is probably enough time to deter a predator from attacking.
Without more information about what our reader found in the dirt, it is difficult to be certain what she is dealing with, but hopefully we’ve covered the relevant information and have helped her with her concerns.
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