Chas, as Timbersmith said. They're many different kinds of leeches but if you're in North America you could probably do an online search and pretty quickly have your answer. Most around NA can be confused with a worm or slug. In-the-water-habit for the aquatic type of leech is one clear way of differentiating it. My understanding of it is that there are terrestrial leeches (I don't know if there are terrestrial leeches in North America). My neighbor is the real expert though. He's a Curator & Professor of Herpetology. If you have any questions or pictures I could take it 'em to him.

Khalid wrote in another thread: "Then I stopped spraying even any organic matter. I gave more calcium to my roses which made the soft branches and leaves harder thus making it relatively unattractive for the pests. This reduced the affected bushes / leaves to a good extent." Agree with Khalid, folks in rainy climate lime their soil, either in late fall or early spring, depending on how many inches of rain they get. Rain is acidic at pH 5.6, as the pH drops, less calcium and potassium are available. The best lime to use is Espoma Garden Lime (sold at Walmart for $10 per 5 lb.). It has 20% calcium and 10% magnesium ... both are essential in keeping leaves thick so pests cannot invade. From the above chart, around pH 5.6 (rain water), less molybdenum, less magnesium, less calcium are available. Next nutrients that are less: phosphorus, potassium, and nitrogen. I already posted in Organic Rose my experiment that I did with 2 identical Thai basil: I lowered the pH of one with acidic cracked corn (pH 4), plus gypsum (17% sulfur) .. that Thai basil' leaves became pale, plus THINNER due to less calcium and magnesium available. Then I saw blackspots on a Thai basil for the 1st time !! The other basil I planted in my alkaline clay (pH near 8), and it's twice taller plus really thick & glossy leaves (more available nitrogen, potassium, sulfur, calcium, and magnesium). But leaves were just a bit pale due to less iron at high pH, so I gave it blood meal, has chelated iron, and leaves became dark green. I once planted a bok-choy vegetable next to my patio with a limestone base, so the soil is very alkaline, pH 8. The leaves were dark-green, but its so tough that I boiled it for one hour, and it's STILL so fibrous that my teeth can't handle, let alone some tiny pests like aphids, rose slugs, or midge. Rose slugs (sawfly larvae) are very rare in my alkaline clay, unless I lower the pH with my experiments: Put acidic cracked corn (pH 4) in potting soil, and roses got rose-slugs from THINNER LEAVES in acidic rain (calcium, magnesium, and potassium drops when pH drops). Mirandy rose got a big-fat rose-slug on it for the 1st time. Why? It's next to a tree, and the tree robs the soil of calcium, magnesium, and potassium. Plus tree roots secret acid, so the soil became even more acidic with rain (pH of rain is 5.6). Used molasses, plus vinegar, plus sulfate of potash (21% sulfur), plus gypsum (17% sulfur) ... such acidic solution made leaves thinner, plus the stinky molasses really attract sawfly which give birth to rose-slugs. CONCLUSION: The best solution for pests is to raise soil pH by using dolomitic lime such as Espoma Garden lime (20% calcium and 10% magnesium). My soil is dolomitic clay, so I don't have midge, rose-slugs (sawfly larvae), nor aphids, unless I use acidic fertilizer. When there's tons of acidic rain, I throw pea-gravel on top of roses that like it alkaline, pea-gravel has many alkaline minerals to make leaves thick, glossy, and to prevent pests.

Thanks for all the comments and helpful hints. I put the cheap Walmart dry dog food out in the evening and kill the diners at about 9PM and maybe again at 10PM. By morning it is typically gone, even though it was often sprayed with the ammonia. As it will stay light later I will have to adjust the schedule. Recently my nightly kill dropped to 20 one night, so I skipped about a week. I will put out the dog food tonight. Ok this will sound gross, but they also like chewed up chocolate or chocolate cookies. The very weird thing is I had a liquidy chocolate that I deposited on the ground. I did this about 4:00PM, then went to a play. Came back and checked about 9PM. I thought that the way the chocolate dropped to the ground and worked it's way into the dirt that they would be working on the chocolate awhile. Surprise, the Chocolate was ALL GONE, not a trace in all 8 spots. Wish I saw what happened. I may try that again tonight.

I have a bunch of hazel seedlings, some in the porch and some planted last year. The slugs here, Canada, leave them alone. I'll be likely having some hazels come up outside shortly, as I planted beaked hazel nuts, so I'll know better if tender new seedlings are tasty to slugs. What kinds of hazels do other folks have?