Insect excreta
Do small insects like mosquitoes and ants excrete solid waste? Are these excreta visible to the naked eye?
P.K. VISVESVARAN , Chennai
Insects feed on different types of food and the nature of their excretory materials mainly depends on the type of foods that they consume. Insects feeding on liquid diet generally excrete liquid waste, whereas insects feeding on solid food produce dark coloured fecal pellets.
The excretory substance of an insect is discharged from the anus and it contains the undigested food from the gut and metabolic excretions from the Malpighian tubules, the slender outgrowths of the gut that float freely in the blood. Insect gut is composed of fore-, mid- and hind-guts.
The semi-solidified wastes and undigested food wastes move to the hind-gut and become part of the feces. The rectal pads in hindgut reabsorb most of the water, salts and other molecules in the feces. Finally, the remaining undigested food materials and the semi-solid wastes are excreted as feces.
Adult mosquitoes of both the sexes feed on nectar and other sugar sources. However, female mosquitoes necessarily feed on blood meal to produce more eggs.
The proteins in the blood meal are hydrolyzed in the midgut into free aminoacids which are essential for the synthesis of its egg yolk proteins. Because of the liquid diet, mosquito adults excrete the sticky feces. However, the feces are not visible unless a large number of mosquitoes excrete in a confined area.
The excretory wastes of ants cannot be generalized since there are several thousand ant species present and their diets greatly vary. Since ants are social insects that live in colonies, they mostly have an organized waste (including excretory wastes) disposal or utilization.
Ant species such as African weaver ants deposit fecal droplets containing a colony-specific material surrounding their nests. A few other ant species maintain external waste heaps outside their nests.
However, these waste heaps are not only meant for the excretory wastes, but also for different wastes from the colony. Hence, it is extremely difficult to see the solid or liquid excretory wastes of small insects, unless they are produced by a group or colony in a confined area.
R. SRINIVASAN
Entomologist and Head of Entomology Group
The World Vegetable Center
Tainan, Taiwan
