Albizia, by their stamens, which are not joined at the base. Also, unlike individual Mimosa flowers, those of Acacia have more than ten stamens. The plants often bear spines, especially those species growing in arid regions. These sometimes represent branches that have become short, hard, and pungent, though they sometimes represent leaf-stipules. Acacia armata is the kangaroo-thorn of Australia, and Acacia erioloba (syn. Acacia eriolobata) is the camelthorn of Africa. Acacia seeds can be difficult to germinate. Research has found that immersing the seeds in various temperatures (usually around 80 °C (176 °F)) and manual seed coat chipping can improve growth to around 80%. Symbiosis In the Central American bullthorn acacias—Acacia sphaerocephala, Acacia cornigera and Acacia collinsii — some of the spiny stipules are large, swollen and hollow. These afford shelter for several species of Pseudomyrmex ants, which feed on extrafloral nectaries on the leaf-stalk and small lipid-rich food-bodies at the tips of the leaflets called Beltian bodies. In return, the ants add protection to the plant against herbivores. Some species of ants will also remove competing plants around the acacia, cutting off the offending plants' leaves with their jaws and ultimately killing them. Other associated ant species appear to do nothing to benefit their hosts. Similar mutualisms with ants occur on Acacia trees in Africa, such as the whistling thorn acacia. The acacias provide shelter for ants in similar swollen stipules and nectar in extrafloral nectaries for their symbiotic ants, such as Crematogaster mimosae. In turn, the ants protect the plant by attacking large mammalian herbivores and stem-boring beetles that damage the plant. The predominantly herbivorous spider Bagheera kiplingi, which is found in Central America and Mexico, feeds on nubs at the tips of the acacia leaves, known as Beltian bodies, which contain high concentrations of protein. These nubs are produced by the acacia as part of a symbiotic relationship with certain species of ant, which also eat them. Pests In Australia, Acacia species are sometimes used as food plants by the larvae of hepialid moths of the genus Aenetus including A. ligniveren. These burrow horizontally into the trunk then vertically down. Other Lepidoptera larvae which have been recorded feeding on Acacia include brown-tail, Endoclita malabaricus and turnip moth. The leaf-mining larvae of some bucculatricid moths also feed on Acacia; Bucculatrix agilis feeds exclusively on Acacia horrida and Bucculatrix flexuosa feeds exclusively on Acacia nilotica. Acacias contain a number