The Hemiptera are divided into 2 sub orders.

Above the sap-feeding hemipteran gut showing how excess water and sugar can bypass the mid gut and be quickly excreted. Below a winged aphid.

Aphids feed on the phloem sap of plants. This liquid is very sugar-rich, (think of maple syrup), has a high water content, but is low in nitrogen. So the bug must eat large quantities to get sufficient nitrogen. The gut is modified so that the excess water and sugar can quickly pass from foregut to hindgut then rectum, bypassing the midgut (see top right which shows the sap feeding hemipteran digestive tract). The midgut is where the nitrogen and the amino acids are absorbed. This means that the excreted liquid is very sweet, and it is sometimes called honeydew. Some aphids can excrete as many as seven droplets of this sugar-rich liquid an hour - that can be as much as 133% of the insect's weight! And some hemipterans consume more than 100 times their body weight per day.

Ants collect or "milk" aphids, but when there are no ants around to collect the honeydew the aphids flick or squirt the droplets away. Sometimes the honeydew is in quantities large enough to be used by man. In the Old Testament the manna given to the Israelites was probably anal excretions of Trabutina mannipara, which feeds on the tamarisk. The Arabs still collect it today, and call it "man". The Australian aborigines also collect honeydew.

They are also prodigious breeders. Females can give birth without mating (parthenogenesis). During summer the young are born live, and one female can give birth to numerous females in a day.

Some aphids have wings and others are wingless, see the drawings left and below.