The BERLESE mounting medium

The preparation method described here is suitable only for small worms, insects, arachnids and other small animals with a more or less stable cuticle. So first try to get adequate specimen! To do so, use the device outlined here ("BERLESE-funnel"). Fill it with a sufficient quantity of decayed leaves and humus from the layer which is located between the upper layer of dried leaves and the topsoil. The heat of the bulb and the increasing dryness of the upper layer of the funnel forces small animals to move downwards where they finally end in alcohol of 80% - what a nice way to pass away! Methylated spirit of 80% is sufficient. After about 24 hours the procedure is completed.

A BERLESE funnel can be easily made from cardboard, but sheet metal is preferable since this material transports heat much better to the lower part of the device. The lower opening should be closed with a wire mesh. Textile nets are inadequate as the animals will not pass this material.

Safety note: Never leave the funnel unattended as accumulation of heat in the then dry upper layer may cause fire!

To produce prepared micro slides you need the BERLESE mounting medium. This is a highly concentrated solution of chloral hydrate and gum arabic in water, which penetrates in a short time into the objects and dissolves almost all soft tissues, making the objects transparent. This process takes several days, sometimes some weeks, and it may happen that the objects become completely opaque for a few days first. The BERLESE mounting medium can be bought in shops for school supplies. We do not recommend to prepare the solution yourself.

The preparation method is very simple: As BERLESE solution does not tolerate alcohol, put the objects into water for one day to remove the alcohol completely, then position the wet objects on an object slide, cover them with plenty of BERLESE mountant and cover with a coverslip. In case of thicker objects put some splinters of coverslips between coverslip and slide. The bleaching process usually is completed after a few days, but then it takes at least another month until the mounting medium is solid. So keep the slides in a horizontal position. The objects cannot be stained because BERLESE dissolves or distroys almost any dyestuff, only soft tissue staining with "nuclear fast red aluminum sulfate" and similar mordant dyes (BECHER-dyes) are possible, but not very useful, as BERLESE solution leads to a severe damage of soft tissues. The coverslides need no ring of varnish. The prepared slides are stable, but temperatures below zero may cause irreversible damage, because the chloralhydrate will form crystals. In that case remove the coverslide by simply covering the whole slide with water for some days, then make a new prepared slide.