A reader asked us through the All About Worms Facebook page about “white worms with yellow bottoms [that are] eating my Dogwood trees.” These white worms with yellow bottoms are very likely white larvae with yellow bottoms, so we’ll adjust our usage accordingly. The reader asked us for an identification, and we’ll largely limit ourselves to this specific matter to keep things short and simple.
The reader submitted no picture, and this normally hinders identification efforts. This is true in this case as well, but the reader gives us some pretty decent information to work with, so the lack of a picture isn’t fatal to our task. Still, an image would be nice, especially because it isn’t entirely clear how we should understand “bottom.” Is this the underside of the creature, or is it perhaps one of its body ends (like its tail end)? Basically, we aren’t sure whether the larva’s change in color takes place horizontally or vertically.
If it’s the tail end, we suspect our reader is finding a pest that is closely tied to dogwood trees – dogwood borers. More precisely, our reader would be finding the larval form of dogwood borers (because she presumably wouldn’t refer to an adult borer, which is a moth that looks a bit like a wasp, as a “worm”). Dogwood borer larvae are what cause harm to trees (dogwood or otherwise), so the larvae are more conspicuous than the adults, at least from the perspective of someone trying to manage their trees. These larvae are a white or off-white color, but they can also be yellow or tan, and sometimes they are even vaguely pinkish. They have brown heads that are clearly distinguishable from the rest of their bodies, so if the non-head part of the body is its “bottom,” they kind of match our reader description. Alternatively, the non-head part of the larva’s body could be white, and its tail end might be more of a yellowish color, and this too would basically match the reader’s description.
Given the information we were supplied with, we think this is as good an identification as any, but we don’t want to imply that dogwood trees only suffer from the borers that are named after them. There is a fairly vast array of different creatures, ranging from aphids to leafhoppers, that might go after a dogwood tree. Of course, most of these creatures, in immature or mature form, wouldn’t be described as worms, but at least one other might – a sawfly larvae. There are many different sawfly species, and some of them have yellow undersides, but we don’t know any that would be described as “white worms with yellow bottoms.” They are generally quite colorful, with their bodies displaying green, black, and yellow patterns. Still, we think they are worth mentioning because the larvae are found on dogwood trees with some regularity, and perhaps there is some species that is predominantly white and yellow.
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As is often the case, we aren’t in a position to make a definitive identification. However, we think our reader should investigate dogwood borers, and she might also look up a list of pests that people find on dogwood trees to see if she finds a better match. In any case, we are quite confident she is finding some sort of insect larva, so that should orient her in the right direction.