Very occasionally I notice small, white worms to be present amongst brine shrimp.
What are these white worms and is it okay for my fish to eat these?
Those small white worms are the larvae of brine flies (Ephydra sp.), also called ‘salt flies’ or ‘shore flies’. As the name implies brine flies live in and near saline lakes, saline ponds and solar evaporation ponds in saltworks. Brine fly and brine shrimp are what’s called ‘co-inhabiting species’[1], which basically means that ‘where you find one of the species, you will more than likely also encounter the other’. And indeed, brine shrimp and brine fly are the only metazoan (so multicellular) species known to be able to permanently live in such saline lakes.
Brine fly larvae live on the bottom of the lakes where they graze on microalgae, bacteria and detritus. They occasionally get dislodged by currents caused by wind or rain and can therefore end up getting harvested together with brine shrimp. Although maybe unsightly to some people, these larvae are actually very nutritious and will be readily eaten by your fish, amphibians and aquatic invertebrates. In nature the larvae are mainly eaten by wading birds[2] and to a certain extend by water boatmen, as fish and amphibians cannot live in these lakes or ponds due to the high salinities (water boatmen only occur at the lower salinity range in which brine fly larvae can be found). As such brine fly larvae play an important role in the recycling of nutrients in saline bodies of water.
Adult flies can literally color patches of beach black because of the sheer, massive number of adults gathering together. Do they form a nuisance for us when harvesting brine shrimp? Not really, as the adult flies don’t fly up to people (they more than likely consider us predators). And besides, during the adult phase the flies only live for a couple of days and the only thing they are occupied with is finding a mate.
[1] Herbst, David B. (1999) "Biogeography and physiological adaptations of the brine fly genus Ephydra (Diptera: Ephydridae) in saline
waters of the Great Basin," Great Basin Naturalist: Vol. 59: No. 2, Article 3.
[2] Roberts, A.J. (2013) “Avian diets in a saline ecosystem: Great Salt Lake, Utah, USA”, Human-Wildlife Interactions 7(1):158-168.