The Whistling Thorn Acacia (Acacia drepanolobium) is a species of acacia tree. They grow in many of the rainforests around the world and also in the Acacia Highlands of Kenya in Africa.

As protection against the many herbivorous forest creatures, the whistling thorn is armed wth two types of thorns. One type are pale color and grow in pairs on the tree. They are very sharp and stiletto-like and can grow up to three inches long. The thorns grow from a hollow, bulbous swelling on the tree. Tiny holes can be seen in them, which act like a flute in the wind, producing the whistling sound for which the acacia is named.

The whistling thorn is also occupied by ants, some species of which live nowhere else. These ants live in a symbiotic relationship with the tree.


The swollen, hollow thorns and thorn base provide a perfect shelter for the ants. Environmental conditions seem to prevent the ants from nesting effectively in the ground. Also, special glands on the tree, called "nectaries", produce a sugary excretion that is a perfect food for the ants, and see to be produced for that purpose alone. When the ants lay their eggs inside the thorn base, they harvest several oval shaped polyps, called "Beltian bodies" that grow from the tips of the tree's leaves. These bits provide nourishment for the developing ants.

As for what is given in return to the tree, the benefits vary on the sies of ant living in the tree. There have never been more than one species living in the same tree because of a violent intolerance for each other. Generally, though, there are only four different species which live with the tree.

Two of the species are very aggressive, swarming and biting any intruder who so much as shakes a branch. This provides great protection for the whistling thorn, warding off any animal that may try to eat from it. Often, vines will attach themselves to the trees in an effort to so up the sunlight that is often scarce beneath the rainforest canopy. The ants will then sever the vine, removing it from the tree, practically ensuring the acacia's survival.

The other spees are far less aggressive, retting into the shelter of the tree at the first sign of trouble. However, if the disturbance starts, the ants will eventually attack the intruder.