Pill bugs, sow bugs & 'Roly-Polies'
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- --- Brett in Oklahoma City, OK
- ---Tracey; Trenton, NJ
- ---Patricia in Lawton, OK
- ---Tony in Brown City, MI
Isopods, not insects, these cousins to crayfish have more in common with crabs and lobsters than cicadas and ladybugs. And although they can be pestiferous under the right conditions, they more often take the fall for some other creatures' crime. When I get emails about them, I write back to explain that they mostly live on decayed plant material and to ask if the writer is SURE that they're the ones doing the damage.
…To which Brett in Oklahoma City replied: "I'm not 100% sure, but there are holes in the leaves of my hostas, and the sow bugs are the only things I see". Patricia in nearby Lawton said: "Well, I was sure until you told me that they mostly eat dead plant material. Now I'm at a loss. They're the only thing that comes out when I water"!
No surprise there. To say that woodlice are fans of moisture is putting it mildly. All of their relatives live IN water, their bodies are NOT watertight, and so their entire life is an endless search for moisture, which is why we often see them around compost piles and mulch—they always gravitate to the moistest area around. And when they're in mulch they don't need to attack your plants; they prefer that nice wet, dead plant material. Yum.
So, 'who' is to blame here? I pick slugs out of the pestiferous lineup. They live in the same kinds of overly-moist conditions, and I often see woodlice (and millipedes) move in after slugs have chewed the first holes in things like strawberries or tomatoes. And Brett even mentions "holes in his hostas"; that's a positive ID! Hostas are the favorite food of the nasty little slimers. Book 'em, Dano!
If you want to make SURE, wait till after dark and go out to the affected area; you may already see slugs massing for an attack. If not, crack a beer, pour some into little margarine tubs, place these around the plants and then check them in the morning. Odds are they will be filled with dead drunken slugs. Control those slugs and I'll bet your problems will be over. Here's a previous Question of the Week that outlines your slimy terror control options.
To keep woodlice away from young transplants and tasty things like strawberries (both of which they are known to occasionally attack), move any mulch a foot away from the plants and ONLY water first thing in the morning, so the ground will be dry by the time they come out at night. You can also leave some mulch or plant debris nearby to decoy and/or trap them. And this may go without saying, but never let tomatoes sprawl on the ground—or everything BUT you will dine on them.
Question. Every time I turn my compost, lots of sow bugs scurry for cover. I generally nurse my compost along until February, and then spread it throughout the garden before planting. I don't see a lot of sow bugs among my plants, but I do plant seedlings throughout the season. Are the sow bugs a danger to those plants—or to my compost?
- ---Vicki in Palo Alto, CA
And if a sudden woodlouse population explosion coincides with really wet weather, sprinkle some diatomaceous earth around your plants. Available at most garden centers (generally labeled for slug control), "DE" looks like flour and is soft to our touch, but it's actually very sharp on a microscopic level. The mined remains of ancient sea-going creatures called diatoms, it is death to soft-bodied pests like slugs and creatures of moisture like our little friends.