Hyalella azteca is a widespread and abundant species complex of amphipod crustacean in North America. It reaches long, and is found in a range of fresh and brackish waters. It feeds on algae and diatoms and is a major food of waterfowl. Description Hyalella azteca has body plan similar to most amphipods and is a classic freshwater example of the order. They grow to a length of , with males being larger than females. Their color is variable, but the most frequent hues are white, green and brown. They are identified from other similar species by antenna 1 being equal or shorter than antenna 2, 1 spine on each plate 3rd and 4th from the last on the dorsal side, Pereopod I and II are gnathopod with males having a visibly larger gnathopod. Distribution Hyalella azteca is found across Central America, the Caribbean and North America, as far north as the Arctic tree line. It lives among vegetation and sediments in permanent bodies of freshwater, including lakes and rivers, extending into tidal fresh water, and freshwater barrier lagoons. It is "the most abundant amphipod of lakes [in North America]", with golf course ponds sometimes supporting large populations. Ecology In contrast to other species of Hyalella, H. azteca is extremely common and has wide ecological tolerances. It can tolerate alkaline waters and brackish waters, but cannot tolerate a pH lower (more acidic) than 6.0. The main foodstuffs of H. azteca are filamentous algae and diatoms, although they may also consume organic detritus. It cannot assimilate either cellulose or lignin, even though these biomolecules are a major component of the leaf litter. It can, however, assimilate 60%–90% of the bacterial biomass that it ingests. Hyalella azteca is an important food for many waterfowl. In Saskatchewan, 97% of the diet of female white-winged scoters was observed to be H. azteca, and it also makes up a significant part of the diet of lesser scaup. Insecticide resistance Some H. azteca have evolved insecticide resistance. This does however conflict with their need to adapt to climate change: Fulton et al 2021 finds some of their mechanisms of resistance impose a fitness cost under higher temperatures. Life cycle Hyalella azteca passes through a minimum of nine instars during its development. Sexes can first be distinguished at the 6th instar, with the first mating occurring in the 8th instar. Subsequent instars, of which there may be 15–20,