Beetles among flood refuse


The warmer months are in many ways the best time for finding beetles; adults are active on vegetation or on the ground and so are easily sampled, at this time also many seasonal groups are present e.g. longhorns and cardinal beetles, and a few seasonal events such as hawthorn and umbels coming into flower or wetland margins drying out provide many opportunities for sampling a wide range of beetles with relative ease. This is also the time when things get moving at night, lots and lots of things. Saproxylic beetles are active and easily found and water beetles become common in the spring. All these beetles are present year-round, in various stages, and many overwinter as adults. But there is one huge disadvantage to collecting during the warmer months and this is obvious from the number of posts on various wildlife sites on social media, and that is, with the possible exception of bird watchers, people do not like going out recording or sampling beetles when it is cold. The overwhelming reason for this is that it is usually uncomfortable; it is cold and everywhere is damp, beyond this the weather is unpredictable and many sites become inaccessible due to water-logging or exposure; a chalk hillside exposed to the sun is a delight in the spring but another matter altogether during the winter. Then there are the beetles, many winter outings produce disappointing results and it does not take many of these before interest begins to fade. Turning logs or searching under bark during the winter will produce plenty of specimens but little diversity unless a great deal of effort is expended, likewise for sweeping vegetation or beating ivy etc., but there are two methods that can be used through the winter that can produce really good results with relatively little effort, and most of the interesting work can be done comfortably inside. These methods are sampling grass tussocks and collecting flood refuse. Tussock sampling is a wide subject which we hope to cover in another article, but here we look at flood refuse.

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Flood-refuse can be collected and examined at any time but it is much less productive during the warmer months because beetles are more active and can, to a greater degree, escape flooding by climbing stems, running or taking flight. But beetles are much less active during the winter because it is cold and they are largely ectothermic and therefore mostly sedentary, thus many will remain stranded, usually along with considerable quantities of organic matter which they tend to cling to for some time. All beetles are present year-round and many overwinter in their early stages but many more do so as adults and, for obvious reasons, they tend to do so in secure and sheltered places, either among organic material near to their natural habitats or in soil near to their host plants or natural haunts. Many choose grass tussocks and these overlap with the present discussion as they can become waterlogged like anything else, the difference here being that tussocks often retain pockets of air among the tightly-packed leaves at the base and these can maintain overwintering insects when the surrounding ground is waterlogged or flooded. So, during a flood, which does not need to be a river or lake overflowing, it can be the result of prolonged local rain which causes the land to be covered with water, the soil becomes saturated and all the organic stuff begins to float. Insects escape the ground because they do not want to drown and, with very few options, cling to the floating stuff until the water recedes. Collecting the floating stuff will therefore produce insects, but some floaty stuff is better than others. This method is obviously good for flooded fields etc. but with a little imagination it can be applied to other situations where excellent results can be had e.g., following autumn ploughing and sowing, an arable field will invariably have a deep furrow along one or two of its margins, these can become waterlogged and full of floating organic matter which may include a wide diversity of beetles. Permission should always be sought and here it should be understood that the vast majority of farmers are very understanding and accommodating, but also that the vast majority also have access to shot guns. Flooded arable land is often easily accessible from nearby roads and it is naturally a good place to sample as many beetles that are active through the milder months tend to migrate away from the fields and to the margins for the winter. Good results can be had from samples of moss or decaying fungi scraped from the ground and bagged, many samples will include leaf-litter or organic debris and these are often good as well, but less obvious samples should also be taken e.g. loose bark from floating logs can be removed and bagged, and even logs and other floating debris is often worth taking for examination.


It should be understood when starting out that many samples will be disappointing, that much of the usual diversity will involve ground beetles and rove beetles and that these usual suspects will occur again and again. This is especially the case when flood refuse is taken close to waterside habitats, from reed bed margins and the like. This is understandable because flood refuse will generally only contain species that have been displaced from their natural overwintering sites. It follows that to get varied samples, flood refuse should be collected from areas that are not normally subject to inundation. This is what the coleopterist should look out for; by monitoring local rivers, lakes and other water bodies through the winter it will soon become clear when the best times for collecting samples occur. These are usually when e.g. water from a flooded area begins to recede and a floating strand line, consisting of all the organic matter that has floated up from the ground begins to form. This will soon be left in lines as the flood abates and at this time the beetles will slowly begin to leave in order to find safer refuges. Freshly stranded lines or piles of vegetation make the best samples, and logs and other floating debris will often harbour many specimens. Taking samples requires a good deal of common sense, along with a decent pair of waders, and it cannot be stressed strongly enough that taking them from riparian situations that are still partly flooded can be very treacherous and in general is a stupid thing to do. But coleopterists, being lots of other things but not in general given to that kind of stupidity, will know when not to push their luck and will be content to take samples from areas that are obviously safe. Do not underestimate how dangerous this can be. I write from experience; it’s one thing having a boot fill up with freezing cold water, quite another to find yourself sliding down a very slippery bank towards an energetic river in flood. For such reasons collecting flood refuse samples is best not done alone. Good samples may provide many thousands of specimens representing a wide range of species, and with luck such samples may be easily accessible. Less accessible samples are best left alone. When facing a long line of stranded refuse it may be frustrating trying to decide what to sample and there is no simple advice to give here. It is sometimes easy to see where the stuff has originated and when this is the case decisions can be based on which areas are likely to have produced the most interesting specimens, but in most cases the stranded stuff originates from flood plain meadows and grazing etc. and is rather homogenous. This means that a few samples taken from a long line of refuse is much more likely to be representative than a single sample, or a couple of samples, taken from a single site. Single samples can be surprising diverse and rich in specimens but increasing the chances of getting something unusual by taking a series of samples is always a good idea, especially when having gone to the trouble to get out in the winter to do this sort of stuff in the first place is considered.

Samples can be collected by hand or with a net e.g. we have obtained good samples by picking up stuff using a long-handled net from a bridge, they will be wet and voluminous and the usual method of sieving them over a sheet is the last thing anybody wants to attempt to do during the winter in the field. They will need to be taken home. A good method is to use buckets or other large containers with close-fitting lids but these take up a lot of space, at least when they are occupied, and they soon become impractical. Large polygrip bags are very good as they can be flattened to evacuate the air before being sealed and so take up a minimum of space. And for the really enthusiastic there are few things as good as pillow cases, these can accommodate decent samples, they allow any water to drain and when it comes to removing the samples are easy to turn inside out to make sure that nothing has been missed. They are also very easy to clean ready for the next sample. In any case a decent number of sampling containers or bags should be taken into the field and all should come back occupied. As with extraction samples it is often the case that out of several taken from the same site there will be one that is full of beetles while many contain nothing at all.


Processing samples

Dealing with samples is usually time consuming but can be very rewarding. Where lots of samples are involved they can be sealed in polygrip bags and left out outside or in a fridge for a few days without harming the specimens but in any case they should be dealt with as soon as possible. Very enthusiastic coleopterists will tend to take too many samples at first but experience soon shows what can be sensibly dealt with. This applies especially when visiting distant sites during the winter specifically to take samples, but following a few good results many coleopterists routinely take a few sample bags into the field throughout the year and so dealing with them soon becomes second nature.  At home they can be sieved into a tray and the beetles pootered for closer examination but this method is likely to overlook a good number of specimens which tend to cling obstinately to the wet sample. The best method to use is that which the beetles were trying to avoid in the first place i.e.  flooding. Submerging  a weighted sample in a bowl

of water will produce beetles but the water will need to be monitored constantly as some specimens take a while to float and, once exposed to the warmth, tend to swim or take flight at the soonest opportunity. Once on the surface they can be removed easily with a fine brush and tubed. When lots of specimens appear they can be swept off the surface with a tea-strainer which can then be drained of water and tapped into petri dishes. With the lids attached such samples may be kept in the fridge for later examination under the microscope without giving the occupants the chance to escape.

It soon becomes obvious that the limiting factor regarding the number of samples taken from the field is the speed at which they can be dealt with, this is further constrained when things like setting and identification are taken into account. Therefore with experience the number of samples will gradually dwindle to a workable number and, with respect to this, the choice of samples taken in the field will become more critical, but after looking at a good number of samples it becomes naturally easy to be able to choose the right stuff to sample. So, after looking at a few hundred samples from varying situations and over a season or two, it becomes second nature to find and take good and productive samples and to be able to ignore less productive stuff. It is very difficult to give advice on how to choose the best samples, this needs to be learned through experience, or better, by going out with an experienced sampler and taking careful observations and advice. It cannot be stressed enough that the work involved with dealing with samples will constrain the number of samples taken, and this is exemplified by considering the very best method of all for removing specimens from samples i.e. by heat extraction. This method is time consuming and, unless stupidly large equipment is used, can only deal with limited amounts of sample. Extraction equipment also involves financial investment, effort and plenty of space. Ideally a series of extractors would be installed in a garden shed in order to avoid domestic strife, but satisfactory and good results can be achieved with a single small device used indoors. Extraction techniques are simple but there are a few things that need to be learned and which will need to be mastered through experience, in view of this we have explained the basics here. A decent extractor will open a whole new world to the novice coleopterist - it is especially useful when dealing with winter samples but, once mastered, will be used routinely through the year for all kinds of samples.


These brief notes usually end with a list or at least an overview covering what kinds of beetles might be expected from the host plants or methods under discussion, but this would hardly be appropriate here. Of course seasonal adults will not appear among winter samples, but otherwise just about anything might be expected; there will generally be plenty of feather-winged beetles and rove beetles, leaf beetles and weevils will also be well-represented and so will certain dung beetles. In the right situation there will be plenty of hydrophilids, histerids and byrrhids and, of course, in riparian situations, the usual haliplids, dytiscids, and hydraenids etc. It would be fair to say that most of our families might eventually be represented among winter samples, even less obvious ones such as Clambidae, Ptinidae and Coccinellidae. Winter flood sampling also produces species less obvious during the warmer months e.g. corylophids and latrids can be found and dealt with before things get really busy in the spring. It really depends on taking samples at the right time and from a wide range of habitats and locations.