Tetraponera penzigi
Tetraponera penzigi, is a species of ant of the subfamily Pseudomyrmecinae, which can be found in East Africa. It forms an obligate symbiosis with the whistling thorn ("Vachellia drepanolobium"), a dominant tree in some upland areas of East Africa. Description. A worker of "T. penzigi" is typically in length and is black with light brown appendages. Distribution. "Tetraponera penzigi" is native to Kenya, Uganda and Tanzania. Ecology. The whistling thorn produces a pair of straight spines at each node, and some of these have grossly swollen, hollow bases which are used by ants as domatia. Four species of  symbiotic ant use "V. drepanolobium" as host; these are "T. penzigi" and three different species of "Crematogaster". The ants are mutually exclusive, only one species normally occupying a host tree at any one time. "T. penzigi" is often the first ant to colonise young trees, being attracted by the nectar provided by extrafloral nectaries that the tree supplies. As the tree grows, "T. penzigi" ants tend to be evicted by "Crematogaster" ants, which do not feed from the nectaries, and destroy them on trees occupied by "T. penzigi", but not on other trees. The tree benefits from the presence of  the ants because they are aggressive, streaming out of their domitia when disturbed and attacking grazing animals such as giraffes and rhinoceroses; having learned this, the mammals are deterred in their grazing activities. The introduction of the bigheaded ant "Pheidole megacephala" in Laikipia County, Kenya, has disrupted the mutualism between acacia trees and ants. "Crematogaster" ants actively defended the whistling thorn against the bigheaded ants and were all extirpated from the tree. However, "T. penzigi" workers, when present, retreated into their domitia and co-existed with the invaders for more than thirty days. The absence of the fierce "Crematogaster" ants  resulted in the tree being much more likely to be grazed and damaged by elephants.