Category Archives: Insects

The Insects at Mwamba!

Over the past two months, we have been doing a baseline study on the insects at Mwamba. Insects are a fundamental part of the life cycle, and a fantastic way to study effects of deforestation and different habitats. The nature trail here at Mwamba has 3 clearly defined areas of vegetation, so we thought a comparison of the population and order diversity of insects in the 3 different areas would be very interesting to study.

The first area is the old dune forest area, as you first walk into the nature trail, with thick vegetation and an almost completely shaded environment, with leaf litter and sticks covering the ground. The next is the cleared area, which was similar to the canopy forest, before it was completely deforested in 1974. Therefore, now it is entirely exposed, with just grass and soil on the ground, and very few sticks/logs. The final site was the coastal scrub forest (heavily bushed area), making up the far end of the nature trail, with very thick and low-lying vegetation, and again a dense layer of leaf litter and sticks above the soil of the ground.

The method of trapping insects involved putting out a 20 metre transect along an area, and a pitfall trap every 2 metres along the transect, with 10 pitfall traps total. The pitfall traps were highly technical (!) – large margarine containers dug into the ground, covered by a raised slate, to prevent rain or debris getting into the traps. Picture – preparing for some sorting with Alex and Steve!

The results were very interesting! The cleared (deforested) area had the lowest number of insects, for most insect orders (those of cockroaches, spiders, crickets and woodlice), except for hymenoptera (wasps, bees and ants). The 10 pitfall traps caught 290 ants in this area – the most of all the sites! I expected to see the cleared area to have the least insects of all orders. The explanation for this surprise result is that the vast majority of the ants caught here, were of the same species. The species is a very small ant that nests underground (so creates its own shade) – therefore the deforestation had little or no effect on these. We didn’t catch any of the ant species that nest in trees, so these must have all been wiped out with the deforestation.

For insects that require a damp and shaded habitat – especially cockroaches, woodlice and beetles – we caught the most in the heavily bushed area, due to the shade from the sun, and the abundant leaf litter that retains water for weeks after it rains. We also trapped a large number of these in the old dune forest area with suitable ground conditions. However, the lack of low-lying vegetation could be a factor for the lower amount caught there than the bushed area. The cleared area caught a very low number of these insects – as it provided an entirely unsuitable environment – exposed to the sun, therefore no shade, and dry very quickly after rain.

We have now sent off an individual of each species I caught off the museum to be identified (at least 100 species!), and this will add to the species biodiversity list of Mwamba. This investigation will be repeated every year, and at different times of year, to show changes over time in order diversity of insects, and keep increasing the species list!

Robin Harris