My crayfish are covered with small, buff coloured eggs?
These eggs are laid by a small aquatic insect, the water boatman or “corixid”, which is beetle-shaped and has two oar-like rear legs. These insects can be seen darting, very quickly, back and forth to the surface of the dam in shallow water to breath air. Large numbers of these insects mean that a dam is highly organically polluted with very little oxygen, even in shallow water (summer floods are a common cause, but overfeeding can cause this condition, too). The corixids lay eggs on any stationary object (a stick) or slow moving crayfish. Marron are badly affected in polluted dams, but we’ve had no reports for yabbies, which are less slowed down by low oxygen. However, large numbers of corixids are a good indication of a dam which is too rich in decomposing organic matter and microscopic algae. On the other hand, a good indication of a dam with well-oxygenated shallow water is the presence of a small crustacean called a scud (amphipod); these get their oxygen from the water, not the a
