A reader recently wrote to us about a big green caterpillar with distinct body segments, body segments that make the caterpillar look like the Michelin Man, to give our reader’s comparison. He included an excellent picture of the caterpillar he found in his yard with his email, which contained a number of terse, difficult-to-decipher bits of information. From what we can gather, the reader is wondering what the big green caterpillar is, and he is also wondering if it is responsible for some of the lawn problems he has been experiencing. So, we are tasked with identifying the caterpillar and investigating whether this type of caterpillar can do damage to your yard.
Before addressing either question, however, let’s take a look at the picture our reader submitted:
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The caterpillar is by a ruler, but it is difficult to read its numbers. However, the reader informed us the caterpillar is about three inches (7.5 centimeters) long, which seems about right (because you can kind of make out the four- and five-inch marks on the ruler, which of course gives you an inch measurement for scale). What are we looking at?
As we have said many times and will doubtless say many times again, caterpillars are extremely hard to identify simply because there are so many of them. Caterpillars are the larvae form of moths or butterflies, and there are around 175,000 species of moths and butterflies (i.e., there are this many species in the order Lepidoptera). Obviously, seeing a picture of the caterpillar helps, but it is not as if we can look at any given picture of a caterpillar and immediately name the species. Moreover, while it is helpful to know that the caterpillar is green because this narrows the range of possibilities, green seems to be a particularly popular caterpillar color (perhaps because green lends itself well to camouflage). Lots of caterpillars are green, and lots of caterpillars go through green instars (developmental stages) as they mature. (This is yet another reason why caterpillar identification is hard: they change their appearance as they come nearer to pupating.) So, as you can see, the numbers are not working in our favor. Even after looking through two caterpillar identification guides, we didn’t find anything that looks exactly like the creature pictured above.
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Even though we can’t identify the exact species of caterpillar our reader found, it seems fairly unlikely that a caterpillar is responsible for our reader’s damaged lawn, which since late June has turned into a “bump course,” by which our reader means there are small piles of dirt all over his lawn. This is actually a fairly common lawn problem that could be caused by a number of creatures, ranging from crayfish to moles to solitary bees. (Our reader should look into crayfish specifically because he mentioned that he lives by a lake.) These creatures will dig small holes, thus creating small mounds, in a person’s yard for a variety of purposes – to nest, find food, get to a water source, and so on. As far as we know, no type of caterpillar is responsible for this type of lawn damage.
Furthermore, caterpillars tend to be very selective eaters and will often only eat the leaves of the plant or tree they are born on, meaning they generally aren’t lawn pests. Some caterpillars may mix grass into their diet, but this wouldn’t cause the problem that has plagued our reader. Finally, the reader describes fairly extensive damage to his lawn, and if he has only found one caterpillar, as he implies, this suggests that something else is harming his lawn. Even though caterpillars can eat an enormous amount of food, it takes more than one specimen to quickly damage an entire yard. In other words, even if caterpillars could cause that kind of damage, our reader would have to be dealing with some sort of infestation, meaning he would likely find far more green caterpillars around his yard if they were to blame.
Unfortunately, though, all of this is speculation – informed speculation, to be sure, but speculation just the same. We don’t know what kind of caterpillar our reader found, so we can’t simply research one species, decipher its eating habits and behavior, and then definitively acquit the caterpillar of causing harm to the yard. At the same time, there are good reasons to suspect that our reader’s yard is being damaged by a creature other than a caterpillar, so we encourage our reader to investigate non-caterpillar causes.