Your picture looks like dysentery to me. But, you need to have the bees examined. A bee lab tech should be able to diagnose the problem after examining a few bees. There are -- at least -- two endoparasites that are a problem with Bumbles: Nosema bombi (infects the epithelial cells of the midgut) and Crithidia bombi (because each intact parasite has a flagellum, I think it likes the lumen of the gut. A zoonotic trypanosomiasis like Chagas come to mind...ouch). Or, perhaps a Malpighamoeba sp. may be the problem. If the bees are suffering from amoebic dysentery, you'll notice a very odd odour from the feces quite unlike anything you have experienced before. Nosema is devastating, especially to individual Bumbles (the course of the disease is much the same as in Honeybees). But, strong colonies often survive. Crithidia is less virulent but has many subtle ways, more of interest to evolutionary biologists. There are a few papers on Bumble dysentery worth reading. Schmid-Hempel is one investigator interested in endoparasites in Bumbles with an eye to testing evolutionary theory regarding parasite virulence and insect 'immune response' (my interest). I like to read anything with Schmid-Hempel as one of the authors -- just because! Fascinating stuff if you're interested in evolutionary theory. Papers with Brown or Shykoff as authors are very good, too. I'd like to know how your case turns out. Oh, try e-mailing Dr Brown at [log in to unmask] at University of Dublin Trinity College. He's interested in Bumble poop. From this North American's point of view, he's so close to you e-mailing seems extreme. Try shouting. We yodel. Best regards, RG :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: -- Visit www.honeybeeworld.com/BEE-L for rules, FAQ and other info --- ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::