I just got done with a my Growing Cool Season Crops class today and someone asked about those white grubs in the soil when they were turning it over. So I dug out this post I wrote in 2012 about what are those white grubs in the soil. I told the class I would put pictures up of the grubs and cutworms so you can know how to ID each of them. One is harmless and the other can be a real problem. Read on.
This time of year when you are adding amendments and turning your soil, you may notice some white fat grubs with brown heads. I noticed they were in soil that I heavily amended with horse manure and would freak out when I saw them. I took all of them (sometimes a lot) and give them to the chickens. I use to think were cutworms but they are not.
They are Scarab beetle larvae and will NOT harm your vegetable plants or vegetable roots. They are also known as the ‘dung beetle’ larvae. In fact they are beneficial because they help break down the manure by eating it, hence you will find them where you use manure. Just leave them alone as they are kind of like worms, adding nutrients to the soil as they process the manure. I have never seen any damage to vegetables but if they are in your lawn (what lawn?! LOL) they will eat grass-roots (but not vegetable roots).
cutworms
On the other hand, here is a picture of cutworms which are HARMFUL to your plants. They come out of the ground at night and chew the base of your transplant stem off leaving you with a decapitated plant (so to speak). They attack baby plant stems because they are tender. After the plants get older, they don’t bother them. If you see these, get rid of them. I look for them in the soil around the hole I dig just before I put my transplants in the ground. But there is something else you can do to protect your plants.
You can protect your plant by putting a ‘cutworm collar’ around your newly planted transplants. I use a paper towel roll or toilet paper row cut into 2 inch increments. I cut the tube lengthwise to get them around the plant stem and tape the cut seam.
Then I sink the tube about 1 inch into the soil. They won’t crawl up the tube. After your plants get a little older, take the tube off-they only like young stems. In this picture the collar is filled with dirt but I just leave the collar on without filling it with dirt.
giantveggiegardener 
Thanks! I wondered about this last year. We had tons of the white ones.
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Just fyi, I cut the bottom out of little paper cups and sink them in, anchored with an earth staple. After the seedling is big and they start to deteriorate, I just pull them up. I have always had to do this with my green beans but did not know what was eating them. This was a great blog. Thanks!
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Afraid I must disagree with your statement that Scarab beetle larvae are harmless. Noticed my recently transplanted lettuces were being cut off overnight at ground level in the typical manner of cutworm, (moth larvae) but when unearthing the root, instead of the typical brownish-grey larvae, each time I found a scarab larvae exactly as illustrated in your first picture illustration, right under each plant. The culprits all have long yellowish front legs, orangey-brown heads and show black (digested food remains?) at the rear end.
Hope this helps.
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Hi Richard-Thanks for your input. I’ll have to check this out better but I use to think the scarab beetle larvae were eating the plants too but never saw one on the surface, always deeper. Instead I discovered that the plants were being eaten by a rolly poly bug (many people call them pillbug, sowbug also). I thought were just composters-they are but they also eat seedlings and newly sprouted seeds right down to the ground like cutworms but the culprits were not cutworms. Since I use lots of manure to make my compost for my veggie beds, rolly pollies show up. Like I said they are great composters and my soil is heavily composted. I assume you use manure to make compost too as those scarab beetle larvae are also great composters in helping to break down the raw ingredients. The scarab beetle lays its eggs in the manure.
So take a look at the top layer of your soil and see if you have rolly pollies on the surface or just below, they may or may not be the culprit. If you have them, I use SLUGGO PLUS (not regular SLUGGO) to sprinkle around the plants or where I just planted seeds and it works like a charm. You can get it online and in some nurseries. Then I usually sprinkle it again after they sprout till they get much taller. SLUGGO PLUS has Spinosad in it which is organic. Let me know what you find out, I’m curious!
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