Monday, 15 August 2011

The richness of insect life is staggering

The malaise trap has had its first outing of the summer, ahead of some survey work planned for the coming weekend. The trap is designed to intercept flying insects and resembles a small tent with sloping sides that don’t come anywhere near to the ground. Insects fly into a central vertical panel (which does reach the ground) and, finding their way blocked, they then fly up to the highest point of the roof. It is here that there is a small aperture, allowing the insects through into a collecting bottle.  It is a simple enough arrangement and one which allows me to catch up with many insects that would otherwise be overlooked.

Large (and hence obvious) insects can be excluded from the collecting bottle by using a little piece of wire mesh. In this way you can avoid the capture of butterflies, day-flying moths and the larger bumblebees; these, after all, are species that can be found and identified with relative ease by using other means.

The trap seems to be particularly good at catching small flies and solitary wasps, many of which will take some time to identify. A few more obvious species are usually present in each haul. The other day, for example, there were three brightly coloured ichneumonid wasps, each yellow and black with an elongated body and legs. These were Amblyteles amatorius, their identification confirmed under the microscope, a species that is fairly common on umbellifers at this time of the year. The species parasitizes a number of different moth caterpillars, including some of those species that I am catching in my moth trap at this time of the year.

Also represented in the trap were several different species of hoverfly, some of which can be surprisingly abundant in the garden at this time of the year. There are in excess of 250 hoverfly species known from Britain, with a few new ones added over recent years. This sort of number, coupled with their relatively large size, often well-marked abdomens and subtleties in wing venation, means that this is a group that amateur naturalists often tackle once they move on from butterflies and bumblebees. There are several good publications available and I have been putting these to good use as I have taken more interest in hoverflies over the last couple of years. Unsurprisingly, the group shows a diversity of lifestyles; for example, the larvae of some species are pests of bulbs, while others feed on aphids, making them both a garden pest and a gardener’s friend. The smaller species are some of the more difficult to identify (or find) and this is where the malaise trap really helps, turning up things that I would otherwise miss.

No comments:

Post a Comment