THIS is with reference to the picture of a tree covered in ‘spider webs’ in the flood-affected area of Khairpur Nathan Shah (April 8). Only a day earlier, a freelance journalist had drawn my attention towards the report and pictures posted on the Net by the UK Department for International Development about this phenomenon.

According to the report, millions of spiders have taken refuge in trees due to the floodwater, which is still standing in many parts of Sindh. It is stated that the local people have never seen anything like this before, but they claim to notice fewer mosquitoes because spiders are supposedly capturing them.

Apparently an expert has not examined these trees and the infesting organism. Reportedly thousands of trees have been affected. Anything with certainty can be said only after a close examination, but I highly doubt that these are spiders.

The spiders using a tree just as an abode never smother it in their web in a manner like this. The typical look of this web on the trees in Sindh is like a heavy infestation by spider mites. Although none of the pictures available on the Net is a close-up, all the affected trees (except one) are most probably acacia nilotica trees. The one which I could not identify looks like Salvadora or Zizyphus.

Spider mites are not spiders. They are web-spinning mites parasitising on a number of plant species.

They are serious pests which obtain their food by puncturing the plant cells; a heavy infestation ultimately kills the plant.

There are more than 1,600 species of spider mites the world over, some of which may look like tiny spiders while some others may be hardly visible to the naked eye.

Mostly they infest herbaceous plants, but several species parasitise on trees and shrubs. They spin the web not for capturing insects but for protecting their own colonies against any predator.

The plants under stress are more susceptible to spider mites. The trees surrounded by floodwater are surely under stress due to overwatering.

It is not clear how many trees on how much area are affected, and how many species of trees and other plants are sufferers.

However, acacia nilotica appears to be the main victim. If this is, in fact, a hitherto unrecorded species of spider mite in our area, it is an alarming situation.

The smothered trees would die in a matter of months if the infestation continues as such.

Acacia nilotica is regarded as the ‘golden tree of Sindh’ which, being an indigenous tree in complete harmony with the local environment, has innumerable ecological and economic benefits.

Large-scale death of these trees will be a great damage to the environment and livelihood of people.

The Forest Department and Plant Protection Department should pay immediate attention to examine these trees and identify and control the infesting organism.

PROF(DR) SURAYYA KHATOON Chairperson, Department of Botany, University of Karachi