The forests and woodlands of Nairobi have been looking particularly lush and green for the last couple of months. This is all thanks to the more-than-generous ‘short rains’ that we experienced late last year. Nairobi is an interesting city for wildlife and nature as it has both forests and savannahs right next to traffic jams and high-rise buildings!
For those who have had the pleasure of visiting any forest or wooded area in Central Kenya over the past few weeks, a strange and beautiful phenomenon is on display.
Scattered here and there in the forests are isolated trees that are draped with shimmering silk. The trees marked in this distinctive way are Elaeodendron buchananii, a common tree of the dry evergreen highland forest and riverine woodland. This species also occurs in the Mara region and parts of Western Kenya.
What makes them stand out at present are the beautiful sheets of silk that drape the trees, which can also be mostly defoliated. The silken sheets stretch over the entire tree, typically covering the trunk as well as the branches and what leaves/twigs are left.
The silk is spun by a veritable army of gregarious caterpillars of a group of insects know as ‘Tent Moths’. These moths, in the genus Yponomeuta, have their own Family within the Lepidoptera: the Yponomeutidae.
The Tent Moths are distinctive in that they live in social aggregations and often completely cover the Elaeodendron trees in Eastern Africa. The caterpillars spin the silk from special glands and move about the tree within its protective confines. Elaeodendron trees are also poisonous and this no doubt confers some added advantage to the caterpillars.
The caterpillars are present on the trees for a few weeks and will then pupate in an aggregation, often sheltered by a branch or on trunk. Occasionally they may enter leaf-litter or shrubbery close to the tree. From these pupae a smallish grey moth with spots on its wings will eventually emerge and start the whole process over again by mating and laying eggs on the host trees.
This phenomenon is really impressive and represents a massive investment made through the efforts of many tiny individual insects working together. Insects may be small, but working together they can have a big impact on the world!
More from the world of insects soon!