The Aphid: A Kamikaze Plasterer
Sacrificing yourself to save the group is something that young aphids in the Asian species Nipponaphis monzeni take very seriously. They are willing to sacrifice their lives to save their colony’s "home".
A colony of these Asian aphids consists of hundreds or even thousands of members. They live together in a hard, closed sphere attached to a tree called a gall - which they build for themselves. What happens if their home is attacked, for example by a caterpillar biting a hole in it? The colony sends in its "soldiers": the young aphids. Some of these attack the intruder, while others repair the hole in the wall.
Crust
To seal his colony's home again, the young aphid squirts a slimy repair glue into the holes. This is a combination of fatty substances and the enzyme phenol oxidase. When these coexist within the cells in their body, nothing happens. However, when they burst out and come into contact with the aphid’s "blood" (haemolymph), a reaction does happen: the fats clump together and melanin is formed. As a result, the substance becomes darker and harder. This forms a kind of crust that can reseal the aphids’ home.
Kamikaze
Aphids that do this are like "kamikaze plasterers", since they usually die during the repair. Some become fatally trapped within the spot as it hardens, but most of them lose so much fluid that they shrivel to barely a third of their original body size. They are then so weak that they probably die soon afterwards.
Little bombs
Cabbage aphids are another species of aphid in which individuals sacrifice themselves to allow many others to survive. These aphids extract a chemical from plants that turns them into walking bombs. When they are attacked by a predator, they release a deadly burst of mustard-like poison. Conclusion: aphids may be small, but they seem to be very brave.