Crawlers and fliers – how to study forest insects

Studying insects is interesting yet challenging. Determining individuals to the species level


The presence of birch bark beetles can be detected by their unique eating patterns. ©Stella Thompson

nearly always requires capturing them first, although some species, such as the birch bark beetle (Scolytus ratzeburgi), can be identified by the unique pattern they leave on tree trunks. However, it is almost always necessary to use various types of traps to capture individuals if identifying the insect species present at a certain site is the main objective of a study. For example, butterflies are trapped during the night using light traps, and the occurrence of certain protected species can be confirmed using feromone traps that use synthetic lures as bait. Traps can be dug into the ground, lifted high up into tree canopies, or attached to the insides of hollow tree trunks.

As my PhD research I am assessing how beavers affect forest beetle populations. I have several research questions:  do beaver-induced flood zones have different beetle species assemblages than other areas, do the increased moisture and sunlight conditions in the flood zone affect species assemblage, and do beaver areas advance or hinder potential forest pest or protected species. My research combines a game species with widespread effects on its surroundings and forest beetles, several species of which have become scarce and require protection. Beaver-induced flooding and the species’ habit of felling tree trunks may locally disturb forest owners, but my study is looking into whether beavers’ actions facilitate or disturb forest pests. Combining game and insect research is cool, and generates new information on which to base decision-making for future protection measures, beaver population management, and even for using beavers as a natural tool for restoring degraded wetlands and forests.

Window traps are widely used for determining the insect assemblages of sites. Window traps cannot be used to capture specific insect groups, because all sorts of invertebrates ranging from flies to pseudoscorpions and wasps to beetles creep or fly into them. Window traps are very simple: the trap is attached to a tree trunk or set to hang between two trees. Insects crawl or fly into the plastic plexiglas frame and then fall through the funnel into a liquid-filled container at the bottom. The container is filled halfway with water, dishwashing fluid, and salt. The dishwashing fluid prevents the insects from regaining flight, consequently drowning them. The salt helps preserve the insects until the trap is emptied out, which happens about once a month. I have 120 traps spread out at several sites, so every summer I collect about 600 samples.

Unfortunately other creatures may sometimes end up caught in the window traps. So far I have inadvertently captured a few common lizards and a bat. This is always disappointing, because an individual dying for nothing does not advance research or science in any way. In the same way it is frustrating if you unintentionally set up a trap on a tree trunk that an ant colony uses as its route. Hundreds or even thousands of ants may drown in the window trap. As my own study focuses on beetles, I cannot utilize the ants in any way. At least this does not happen very often.

After the trap container has been emptied the gathered sample is sifted through using tweezers and a microscope, to separate the insect groups that I am interest in. Next the individuals are determined to the necessary level. Sometimes determining the family level is enough, but if making conservation decisions or gaining new information on certain species is the goal, it is usually necessary to determine individual insects to the species level. How this is done depends on the order in question, e.g. beetles are often recognized by their ankles and genitals.

Occasionally you come across data deficient species, i.e. species that are not well known or understood. Species, genera, and families are determined using identification keys, which are sometimes incomplete. For example, currently the best key for identifying Finnish rove beetles is in German, and for several families the most complete keys are in Russian. So I’m currently kind of happy that I studied German in middle and high school. I guess next I should begin uncovering the secrets of Russian vocabulary.


Protecting one of the largest economies in the world

Wetland  ecology group_University of Helsinki_shallow waters of the Baltic Sea

Shallow waters of the Baltic Sea © Stella Thompson

Implementing the Red List of Ecosystems (RLE) has kicked off to a good start. I introduced this fairly new conservation method in a previous blogpost ( So far trial studies have been conducted in cooperation with IUCN on all continents apart from Africa and Antarctica. Several countries (e.g. El Salvador, Costa Rica, Marocco, Senegal) have additionally completed or nearly completed drafts for the RLE assessment of their ecosystems. Norway, Finland, and Australia are furthest in the task of implementing RLE categories and criteria into their national nature conservation standards and biodiversity legislation. A quick look at the different ecosystems encompassed so far reveals that various mires, wetlands, shore environments, coral reefs, and temperate and boreal forests are fairly well represented.

The Southern Hemisphere in particular has stepped up in the concrete utilization of RLE in assessing the health and collapse risk of ecosystems. Through a series of 13 studies, Australian researchers have determined that RLE is a functional tool for classifying and assessing various ecosystems. This has concurrently revealed several practical measures for promoting ecosystem conservation. Within the next couple of years the assessments will be extended to include all ecosystems in Australia. Factors most strongly weakening the health of Australian ecosystems have been gathered together. It is hardly surprising that climate change plays a large part, impairing ecosystems from rainforests to oceans and deserts to dry meadows. However, each ecosystem faces unique challenges at its own pace. This supports the all-round utilization of RLE. We cannot kid ourselves that conserving a few currently unwell ecosystems would be sufficient, but we must also take into consideration the probable changes that will occur in presently healthy or nearly healthy ecosystems in the near future. The future viewpoint should unquestionably be included in national RLE assessments.

A concurrent armament race seems to be ongoing concerning marine conservation; during 2015 at least four countries announced plans of founding the largest marine conservation areas in the world. The Kermadec nature reserve in the Pacific waters of New Zealand will span 240 000 mi2 (620 000 km2), while Great Britain is planning three protection zones in the Pacific and Atlantic Oceans with a combined area of 695 000 mi2 (1 8000 000 km2). Palau ratified the establishment of a 193 000 mi2 (500 00 km2) nature reserve, and Chile declared intentions of founding a marine sanctuary in the waters of Easter Island, covering 243 200 mi2 (630 000 km2). Complete RLE assessments should be conducted on each of these soon-to-be-founded zones, to find the areas that would most benefit from improvement. Assessments have indeed been planned for some of the reserves.

Marine conservation is geared towards securing important growth, spawning, reproductive, and feeding areas. Protecting specific ecosystems, e.g. underwater volcano chains, and securing fishing possibilities are also paramount. A recent WWF report (downloadable at calculates the combined economic value of oceans at $24 trillion. The products and services attainable from oceans is valued at $2.5 trillion. If they were an independent nation, the world’s oceans would be the seventh largest economy on the globe, ranking between Great Britain and Brazil. However, the WWF report concludes that the biodiversity of oceans has decreased by nearly 40% during 1970–2010 due to climate change, seawater acidification, and overfishing. Currently two thirds of our fishing waters have been completely utilized. Most of the remaining areas are over- rather than underexploited. The economic value of oceans is presently dwindling rapidly as marine ecosystems weaken and collapse.

Wetland  ecology group_University of Helsinki_fishing boats on the Atlantic

Fishing boats on the Atlantic Ocean © Stella Thompson

The oceans and seas have long been the Wild West of our planet, where utilization and downright exploitation are permitted with little or no rules (the so-called “tragedy of the commons”). Legislation lags behind the current situation, but founding enormous nature reserves is an excellent way to uphold ocean ecosystem health, at least from the viewpoint of reducing raw material overexploitation. But even huge conservation zones are not sufficient to control the negative effects of climate change.

Marine sanctuaries are an indication of how much we can do to uphold and maintain ecosystem health, especially when national authority and decision-making is combined with international cooperation. Unfortunately the similar protection of land ecosystems is proving more difficult because of intense land use and strict land ownership. The above-mentioned four marine sanctuaries will have a total surface area of approximately 75% of the surface area of the European Union. Conserving such a massive land area would be demanding. International cooperation is the only way forward when dealing with these challenges.


More on the planned marine sanctuaries:

Beavers restore the dead wood of boreal forests

Dead wood is a necessary element for numerous species living in the boreal zone. It functions as a food resource, nesting space or growth substrate for several mammals, fungi, insects, and birds. Dead wood is produced through two main mechanisms: senescence and disturbances e.g. forest fires or wind damage. A controlled forest has less ageing trees and disturbances, and currently up to 90% of Fennoscandian forests have been influenced by forest management. The recent drop in dead wood levels due to intensive forest management across the globe has concurrently led to dead wood-dependent (= saproxylic) species becoming rare as well, which weakens food webs and ecosystem functionality. Managed forests may only contain a few cubic meters of dead wood per hectare, while dead wood levels in old-growth forests and forests influenced by disturbances can rise up to hundreds of cubic meters per hectare.

Beaver, the ecosystem engineer © Sari Holopainen

Beaver, the ecosystem engineer © Sari Holopainen

Strong disturbances are less frequent in moist lowland areas of the boreal zone, where dead wood is mainly created as single trees die due to competition and ageing. However, beavers act as wetland ecosystem engineers, raising floodwaters through the damming of water systems. These floodwaters kill surrounding shore forests due to oxygen deprivation, thus creating significant amounts of dead wood into the habitats. In certain cases the flooding may kill entire forest stands. Beavers can therefore be considered the main natural disturbance factor of lowland forests.

Beavers require wood for food and as a building material for their nests and dams. Foraging for woody materials causes the resource to run out within a few years, forcing the beavers to move location. The process of flooding and dead wood creation begins again in a new area, thus producing a continuation of dead wood hotspots into the landscape. Eventually after several years the beavers can return to a previously inhabited location, which will be then be repeatedly subjected to their engineering. These hotspots may be very important to dead wood -dependent species, especially as they uphold a network and continuous supply of different-aged dead wood.

Calculating dead wood levels at a beaver flood - spot the researchers! ©Mia Vehkaoja

Calculating dead wood levels at a beaver flood – spot the researchers! ©Mia Vehkaoja

Despite an overall decrease in dead wood levels, certain types of dead wood have become rarer in the boreal forest than others. Currently the rarest forms are standing dead trees (snags) and deciduous dead wood. Both have declined more rapidly than other types due to forest management actions and attitudes. Beavers create a broad range of dead wood types (e.g. downed wood, stumps and coniferous dead wood), but they particularly aid in the production of snags and deciduous dead wood. This is good news for many saproxylic species, as these organisms are often strongly specialized, utilizing very specific dead wood types.

The dead wood produced by beaver-induced flooding is also very moist, which may affect the wood-decay fungi species that begin colonizing the dead wood. For example, sac fungi are more tolerant of wet conditions, and may therefore outcompete Basidiomycetes at beaver sites. This in turn will lead to differing invertebrate communities that utilize sac fungi instead of Basidiomycetes. Very different dead wood –dependent species assemblages may therefore be formed at beaver sites compared to fire areas of clear-cuts. The interactions of these species are currently poorly understood.

The beaver offers a possibility for all-inclusive ecosystem conservation compared to the conservation of single species. The species could be used to produce dead wood and restore the shore forests of wetlands.

Our research group has recently published an article concerning the impacts beavers have on boreal dead wood. The article can be accessed from

Calculating dead wood levels at a beaver flood - spot the researchers! ©Mia Vehkaoja

Calculating dead wood levels at a beaver flood – spot the researchers! ©Mia Vehkaoja

An Awful Lot of Voles every five years or so…

Grey red-backed vole (Myodes rufocanus) ©Sari Holopainen

Grey red-backed vole (Myodes rufocanus) ©Sari Holopainen

A recent hiking trip to Lapland got me thinking of voles. The little critters were absolutely everywhere, happily (or with a vengeance) gnawing at our rucksacks during the night in hope of finding food. Several notes left in hiking huts along the way gave more proof of their high numbers: two people had had their rucksacks eaten through and one had lost a bag of nuts when a vole ate a hole through the tent.

Back home in southern Finland, not hair nor hide of a vole. Why not? What actually constitutes a vole cycle, how does it work, and why does it periodically crash? And how does it affect other animals?

Voles can reach sexual maturity as early as three or four weeks, depending on the species in question. This combined with large brood sizes and giving birth to several broods during the breeding season means that when conditions are right there will be an Awful Lot of Voles (called the peak of the cycle). This leads to increases in the numbers of predators (e.g. stoats Mustela erminea and least weasels Mustela nivalis), which marks the start of vole population declines and crashes as their mortality increases. The whole cycle appears to take around three to five years in northern Europe, but it is not synchronous everywhere. Hence a deluge of voles in Lapland, while populations in southern Finland crashed last winter and currently remain small.

Vole populations fluctuate on a yearly basis. Graph by Hannu Pietiäinen.

Vole populations fluctuate on a yearly basis. Graph by Hannu Pietiäinen.

Voles are of course, paramount to many predators. During our hike we saw a hawk owl (Surnia ulula) and several rough-legged buzzards (Buteo lagopus). Signs of martens and stoats were numerous. Unfortunately the elusive snowy owl (Bubo scandiacus) did not make an appearance. These are all species whose life cycles are influenced by voles. They produce larger numbers of offspring during vole-rich years, while breeding may plummet to zero when vole cycles are down. Many strict vole eating owl species are nomadic, wandering large distances to ensure being in the right place at the right time when it comes to food. However, several owl species are residential and will not travel in search of food, e.g. the tawny owl (Strix aluco). For these species in particular the vole cycle does not only determine breeding success or brood size, but actually influences the number of breeding pairs in the total population, the timing of nesting onset, even a young owl’s entire life expectancy and quality of life. For example, the phase of the vole cycle (aka the nutritional state of an owl) during the first year of an owl’s life correlates with the number of parasites it carries as an adult. The vole cycle also determines at what age residential owls are recruited into the population as breeders (e.g. whether at one or two years of age), as owls will not breed if the female is too weak.

Phase of vole cycle affects nesting and owling survival. Modified from picture by Hannu Pietiäinen.

Phase of vole cycle affects nesting and owling survival. Modified from picture by Hannu Pietiäinen.

A worrying phenomenon has possibly begun to unfold during the last few decades concerning vole cycles. Twice the cycle has been disrupted, and an anticipated peak has not occurred. If disturbances in the cycle become more frequent, this will play havoc for countless northern species. The reasons behind this disturbance are unclear, but a warming climate with thin snow cover has been suggested.

Rough-legged buzzards use voles as their primary food source. ©Sari Holopainen

Rough-legged buzzards use voles as their primary food source. ©Sari Holopainen

Hot spots of boreal landscape

The beaver (Castor spp.) is a known ecosystem engineer that modifies its environment quite drastically. It builds a dam and raises floodwaters into surrounding forests, killing trees, and releasing organic material into riverine systems and lakes. The rising water level changes both the abiotic and biotic conditions of a wetland. Many organisms, from water lice to water birds, benefit from these changes. Beavers facilitate these species by offering both nesting and sheltering areas in the form of low bushes and trees by the water’s edge, increased aquatic plant communities for nutrition, and ice-free water areas for extended periods.

Beaver-created wetlands are cyclic ecosystems. Beavers usually inhabit a site for one to three years and then move to the nearby site, where the whole process starts again. After the beaver has left the site, the abandoned site reverts quite slowly back to the original. So the beaver’s actions endure much longer than they occupy the site, and commonly they return to former sites within 10 years.


Beaver-created wetlands can be seen as a biodiversity hot spots. This pic is from eastern Finland. © Mia Vehkaoja

Beaver-created wetlands can be seen as a biodiversity hot spots. This pic is from eastern Finland. © Mia Vehkaoja

The beavers’ actions can be seen as quite sharp shifts in an ecosystem, but the very nature of the changes that the beavers create tends to be rather stable. As the beavers transform the ecosystem they also enable resilience in landscapes. Beaver-created wetlands increase the heterogeneity of the landscape, and can be seen as biochemical and biodiversity hot spots. They maintain several declining species, especially in the northern Boreal Hemisphere, where eutrophic wetlands are relatively rare.
The EU has an ongoing project called the Return of Rural Wetlands. The size of the EU funding in this project in Finland is a little over a million Euros. The other million Euros come from the Finnish Government and the rest from the Finnish Wildlife Agency. The aim of the project is to create a new frame and a good start for the future nationwide program for wildlife habitat conservation, restoration and re-creation. So people are creating new wetlands using tractors and diggers, and by bringing soil and water from elsewhere.

Beavers would do the same work for free. Instead of misspending lots of money on labor, expensive machines and moving earth, we could use some part of the funding to re-introduce the European beaver (Castor fiber) to a wider area. In this way we would save money, get the same results, if not even better ones, and help our original, once extinct species to recover. In addition, Finland would achieve the obligations of EU Inland Water Directive.

The new re-introduction of the European beaver project would involve the same interest groups as the Return of Rural Wetlands project. Some of the re-introductions could be conducted on state-owned lands and some on privately owned land. There are several local landowners involved in the Return of Rural Wetlands project, so there is a good possibility that they would be interested in the same kind of project as well. Regional hunting clubs would want to be involved, as beaver-created wetlands offer improved hunting and fishing opportunities, because their habitat engineering increases the number of game and fish species. It might be easy to get regional authorities and policymakers to engage in the project, because of the EU obligations that abide them. Furthermore, the policymakers would conserve the biodiversity of Finland, and gain the respect of The Finnish Association for Nature Conservation and the public. When all these interest groups are involved in and the role of power is divided to various levels, a revolution in wetland creation is possible. When such a project succeeds in Finland, it should be possible to implement it also in other EU countries.


The Mallard (Anas platyrhynchos) favors beaver-created wetlands, especially during breeding season. © Mia Vehkaoja

The Mallard (Anas platyrhynchos) favors beaver-created wetlands, especially during breeding season. © Mia Vehkaoja

The beaver’s actions extend wider than just creating suitable wetlands for several species. Beaver-created wetlands produce high amounts of dead wood. Dead wood is a decreasing natural source and the species dependent on dead wood are under threat. There are numerous bryophyte, lichen and beetle species that rely on moist dead wood. The resilience of beaver-created wetlands is more general than specified, as its transformability reaches from wetlands into the forest.

Beavers provide also other ecosystem services to humans. They mitigate flood peaks by retaining rainwater and drought conditions by slowly releasing water. Beaver-created wetlands act as buffer zones by filtering impurities, e.g. heavy metals, thus increasing water quality. They facilitate and conserve endangered and declined species, and create interesting hiking and relaxation possibilities for humans. All in all, beaver-created wetlands are one of the key ecosystems in boreal areas to be conserved.

A whole new universe in dead wood

Before I took part in the course Biodiversity in dead wood (organized by the University of Helsinki), I thought that there is dead wood only aboveground. So it was an elevating experience to realize that most of the dead wood is underground. Boreal forests have more underground dead wood than for example broadleaved forests. Underground dead wood is very common in Finland as there are lots of pine-dominant bogs. There pines sink underground before they are decayed, and lots of underground dead wood is produced.

Standing dead pine, possible becoming a kelo. © Stella Thompson

Standing dead pine, possible becoming a kelo. © Stella Thompson

One other special characteristic for Finland forests is kelo, which is a dead standing pine. Usually the kelo has lost its pine bark. Kelo trees have unique biodiversity, which is completely different than for example in dead birch. It is quite typical that the saproxylic species are specific to certain tree species. This feature enhances the saproxylic diversity in forests. Saproxylic species are defined as any species that depends upon decaying woody material.

The carboniferous was a starting point for saproxylic evolution. Almost immediately when the first trees arrived on land, the first decomposing fungi evolved. After fungi the first decomposing invertebrates developed. The rapid specification of the saproxylic species occurred in the Triassic and Jurassic ages. The first termites existed about 100 million years ago. The evolution of saproxylic beetles is better known than the evolution of basidiomycetes. This is due to better preserved fossils.

There are approximately 400 000–1 000 000 saproxylic species in the world, and in the Nordic countries the same number is 7589 known species. Finland alone has 4 000–5 000 dead wood species. This is about 20–25 % of all forest species. It could be argued that there are several unknown saproxylic species in the Nordic countries. Solely in Finland, almost every year new saproxylic species are found. Boreal forests have almost as much dead wood as tropical forests. This correspondence between the two forest types results from the different decaying rates.  The decaying rate of tropical forests is much faster.

Basidiomycetes decaying goat willow (Saprix caprea). © Stella Thompson

Basidiomycetes decaying goat willow (Saprix caprea). © Stella Thompson

The decaying rates also differ in different parts of boreal forests. In the fast-decaying parts 90% of organic matter can be decomposed in 50 years, whereas the same process will take 100 to 200 years in the slow-decaying parts. At an early successional stage the decaying process is usually slow and accelerates towards the pristine forest stage. The main hazard to saproxylic species is forestry. For instance in Finland forestry has reduced the amount of dead wood from 60–120 m3 per hectare to 2–10 m3 per hectare. This reduction is severe. The new trend in forestry, at least in the Nordic countries, is bio-fuel in the form of intensive residue harvesting. This means that even the branches, crowns, and stumps are collected from the logging area. This leads to an even more decreased amount of dead wood in forests. It can be quite easily calculated that without dead wood about 25% of Finland’s forest species are lost. Why is nobodytaking strong action to prevent this from happening? Researchers and conservationists should come together, and force decision-makers to see the dramatic downside of residue harvesting.

Dead wood on top of lingon- and blueberries in boreal forest. © Mia Vehkaoja

Dead wood on top of lingon- and blueberries in boreal forest. © Mia Vehkaoja


Check out also this amazing article about Ancient Forest Found Thawing Beneath Melting Glacier in Alaska


Aliens are among us

The EU announced a new alien species strategy just a few weeks ago. The strategy uses a three-step hierarchical approach: 1) preventing species from entering and spreading in a country, 2) early detection and eradication, and 3) long-term control and spreading prevention. What are the most efficient actions to preventing the spread and/or eradication of alien species?


Alien species are considered one of the greatest threats to biological diversity. Their success lies in rapid reproduction, good tolerance of different environments and a high dispersal ability. So what to do? Prevention is the key. One of the most efficient examples of a country with a very strict controlling program is Australia. The county controls everything that tries to enter through its international borders. Even the dirt on the soles of your shoes is investigated for microscopic aliens. This is no wonder as prevention is the most cost-effective method against invasive alien species. The costs caused by alien species are over 1 400 billion Euros every year.


When an alien species has spread, there are several methods for eradicating it. One can try to hunt down every individual or use pesticides, predators or pathogens against the alien. There are few successful examples of eradications, such as rat eradication in Tahanea Atol to save the endangered Tuamotu sandpiper Prosobonia cancellata, but most of the time the process is difficult if not completely unsuccessful. Pesticides used against plant pathogens or pest insects can seep into the soil and pollute near ecosystems as well as fresh water supplies. Predators can be used to control alien species population levels, but on the other hand finding a predator specialized in one particular species is very difficult. So the downside is that the predator will probably wipe out several other species also.


Are modern-day eradication strategies timely? What if we invest a lot of effort and money into eradication, and the alien species eventually spreads naturally and unaided into the ecosystem due to climate change? This has already happened in Spain, where the human-introduced ruddy duck Oxyura jamaicensis (originally from North America) threatened the rare white-headed duck Oxyura leucocephala. The Spanish government and EU first tried to exterminate the ruddy duck populations but then gave up, as it was quite clear that the species might spread naturally into the ecosystem within just a matter of years.

Alien species don’t just influence nature. They also affect the societies and economies that we live in. The pine wood nematode Bursaphelenchus xylophilus would have tremendous effects on Finnish forest industry if it were to invade Finland. The pine wood nematode is originally from North America, where local pine species have evolved a resistance to the nematode. The pine wood nematode is a real threat to Finland, as it has already spread to Portugal and the EU commission has restricted the export of Portuguese conifers. If the nematode would spread to Finland, the consequences could be devastating not only to Finnish forest industry, but to Finnish society as a whole. The total value of exports by the Finnish forest industry was 10.8 billion Euros in 2010, which is approximately 20% of the total export of Finland. In light of all the negative effects, can the aliens ever be friendly? And can we afford to be friendly in return?