The Venezuelan Cave Cricket – Hydrolutos breweri

Head of a male Hydrolutos breweri. Image: C Brewer-Carias

This month’s curiosity is Hydrolutos breweri, a newly discovered flightless Venezuelan cricket which lives its entire life in perpetual darkness in the freshwater pools and streams flowing through caves atop high mountain plateaus.  As you can see in the video below, Hydrolutos is unlike any entry into the Cabinet so far!

Hydrolutos breweri is a member of a fascinating family of giant crickets from the Southern Hemisphere, the Anostostomatidae, which includes the Australian king cricket – which has been seen to overpower and eat large funnel-web spiders!

The new species was discovered in a gigantic quartzite cave – Cueva Charles Brewer (named after the Venezuelan explorer who “discovered” it, and famous for (amongst other things): “the discovery of the world’s largest quartzite cave and 27 plants, reptiles, insects and a scorpion named in his honour; a raft of diseases including malaria and leishmaniasis in his system; and a record for starting fire with sticks (2.7 seconds)”) – on a mountain plateau in eastern, Venezuela.

Known locally as “tepuis”, such table mountains rise sharply and dramatically up sheer cliffs from the lowlands, isolating the plants and animals they support on plateaus high above lowland ecosystems.

A Venezualan tepui rises sharply from the lowland landscape. Image: wikipedia

This detachment from the wider ecosystem allows species on the high tepuis to evolve in isolation over time, producing an incredibly rich biodiversity, consisting of many plants and animals with curious, unusual characteristics contained in a small area, a phenomenon known as endemism.  This isolated evolution atop high South American mountains inspired Arthur Conan Doyle to write The Lost World in 1912, a novel suggesting that dinosaurs and other prehistoric creatures still survived on such plateaus!

The incredible Cueva Charles Brewer. Image:

In 2010, an expedition was led by Charles Brewer-Carias and Branislav Smida to explore the gigantic quartzite Churi-tepui cave system in the Chimanta mountain range in eastern Venezuela.  The expedition discovered an incredible new insect, named Hydrolutos breweri after the explorer in a 2010 paper published by Tomas Derka and Peter Fedor.

Male Hydrolutos breweri. Image: Mr. Michal Poljak

The newly discovered cricket is found in the freshwater streams and pools that wind through the plateau cave system, where its strong legs and claws (see the picture above) allow it to grip, clamber and swim through a treacherous, slippery environment.  Incredibly, the cricket lives its entire life in perpetual darkness in the cave system.  However, the fact that Hydrolutos breweri doesn’t display any of the usual features of cave-dwelling insects (or “troglobionts”) such as tiny eyes or a whitening in body colour, means that this new discovery is likely to also be found in other streams and pools outside of the cave system.

Hydrolutos breweri in its natural environment. Image Tomas Lanczos

Another fascinating curiosity for the Cabinet of Freshwater Curiosities – who knows what the continued exploration of this amazing cave system will yield?  New freshwater plants and animals are being discovered every year, even in areas thought to be well explored and known – if you haven’t seen WWF’s report on their most recent expeditions in Papau New Guinea (where they found, amongst other things a previously undiscovered 2.5 metre long river shark and a “vampire frog”!), it’s well worth reading.

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Lesser water boatman – Micronecta scholtzi

Lesser waterboatman. Image: Jérôme Sueur

Tiny freshwater bugs create a cacophony in inventive ways…!

This month’s entry into the Cabinet of Freshwater Curiosities is the lesser waterboatman – Micronecta scholtzi – a common freshwater bug that produces a peculiar courtship song by rubbing its penis along its abdomen, a sound which reaches an incredible 99.2 db!  That’s a sound level equivalent to sitting in the front row of an orchestral concert, or standing close to a passing train!

As Dr James Windmill at the University of Strathclyde – a lead researcher on the June 2011 study “So Small, So Loud: Extremely High Sound Pressure Level from a Pygmy Aquatic Insect” published in the open-access journal PLoS – describes:

“Remarkably, even though 99% of sound is lost when transferring from water to air, the song is so loud that a person walking along the bank can actually hear these tiny creatures singing from the bottom of the river.”

The sound, used by tiny (2mm) males to attract mates, is produced by rubbing the penis and the abdomen together, in a process called stridulation. In the lesser waterboatmen the area used for stridulation is only about 50 micrometres across, roughly the width of a human hair.  This stridulation process is similar to that used by grasshoppers and crickets to produce their idiosynchratic chirps and chirrups.

Dr Windmill continues: “If you scale the sound level they produce against their body size, Micronecta scholtzi are without doubt the loudest animals on Earth.”

Animal noise/size comparison. Image:Jérôme Sueur

The loudest human shout ever recorded is 129db by British teaching assistant Jill Drake in 2000.  Sperm whales have been recorded emitting sounds reaching an incredible 236db, a cacophony required to communicate across vast, turbulent oceanic distances.  Decibels are a measure of the intensity or ‘loudness’ of a sound, measured on a logarithmic scale.  This means that for every increase of 10 decibels, there is a 10 fold increase in sound energy.


For comparison, a normal human conversation is generally measured at around 60db.  Incredibly, at 99.2db, the sound made by the lesser waterboatman is almost 10,000 times more powerful!  Whilst completely different in size, the incredible sounds emitted by both the lesser waterboatman and sperm whale, shows how aquatic animals have evolved to be able to communicate despite the muffling effects of the underwater environment.

This remarkable little bug is a fantastic wee addition to our Cabinet of Freshwater Curiosities, and like previous entries the bladderwort, the caddis larvae and the mayfly shows that incredible creatures live in the most everyday, developed freshwater environments: curiosity close to your home.

Let us know your thoughts on the waterboatman in the ratings and comments boxes below, and we’d welcome any budding “Curators of Curiosity” to get in touch using the box on the right with any amazing animals they’d like to see in the Cabinet in the future.

More links and information:

Strathclyde University Press Release on the story

Sueur et al 2011: The original journal article in PLoS One

Wired article on this incredible insect 

Wired article on the “bioacoustics” of animal sounds

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Tisza mayfly – Palingenia longicauda

Long-tailed Mayflies (Palingenia longicauda) hatching in the Tisza River -- Solvin Zankl/Visuals Unlimited,Inc. ©

Guest curator: Following his extremely successful caddis fly entry into the Cabinet in March, BioFresh partner Dr Daniel Hering returns to showcase Palingenia longicaudia, or the Tisza mayfly – Europe’s largest mayfly.  You can find a special series of articles on the fascinating ecological, cultural and recreational importance of the mayfly on the BioFresh blog.

Mayflies are an abundant and diverse insect group occurring in running and to some degree in standing waters. In German, they are called “Eintagsfliegen” which means “one day flies”, as their winged, adult stage is very short – a few hours or a few days as a maximum. Most of their life-time, is spent as a larvae in the water, lasting for one year or more. Most species emerge in synchrony from the aquatic habitat in the summer, creating an incredible natural spectacle as blooms of the insect appear to dance above the river’s surface.

Almost all specimens of a mayfly species tend to leave the water within one or few days, creating huge clouds of swarming insects.  The advantages of this huge, synchronised hatch are obvious: as insects can only mate in their adult stage, by synchronising the hatch,  the chance of finding a partner is maximized – which is very important for species with such a short adult life stage. Predators like bats or birds are surprised by this sudden appearance of clouds of prey, and so can hunt only a small fraction of the population. The vast majority of mayflies die immediately after mating; in some cases the piles of dead mayflies block roads or bridges and need to be removed with a snow plow!

The swarming of mayflies is particularly impressive in case of large specimens, which used to be extremely abundant in large lowland rivers. Due to widespread pollution most of the large river species disappeared from European rivers in the 20th century but conservation efforts in the last two decades are helping some of them return.

Tisza mayfly (image: Lacitot,

However, Europe’s largest mayfly Palingenia longicauda, has managed to retain small but healthy populations around Hungary and northern Serbia.Palingenia specimens are about 4 cm long. They appear to be much larger, as they have up to 8 cm long appendages at their abdomen. The only large population of Palingenia longicauda, which has survived, is based in the Tisza river in Hungary. The species emerges around mid June, and event which is frequently referred to as “Tisza blooming” and is amongst the most fascinating natural phenomena in European rivers.

Tisza bloom (image: The Nature Animals)

This synchronised hatch is one of nature’s great sights, as the surprisingly large insects seem to dance above the river’s surface, smothering the riverbank and any other available surface (including cars, roads and people!) as they seek to find a mate in the short time available to them.  Hundreds of thousands of males fly towards the middle of the river to search for females which hatch at the water surface.  After mating the females may fly several kilometers upstream to compensate for downstream larval drift and laying their eggs along the way.  

And then as suddenly as it began, this fleeting, wonderful natural marvel is over.  Around the end of June the surface of the Tisza is covered with large dead mayflies, spent after their ephemeral existence is over. The larvae resulting from succesful mating grow in holes in the loam of the river bottom for three years, until they hatch and mayfly’s day-long dance is repeated once again.

More information

  • Wonderful gallery of high-resolution photos of the Tisza mayfly here
  • Arkive page here
  • Wild Serbia page on the Tisza mayfly

Arkive footage:

ARKive video - Male Tisza mayflies searching and competing for a female mateARKive video - Tisza mayflies swarming

Caddis larvae – Trichoptera

Micropterna in an artificial case (image: Gerhard Laukötter)

Artistic riverine insects create colourful cases from unusual materials

Guest curators: Prof. Daniel Hering (University of Duisburg-Essen) and Gerhard Laukötter

Many animal species are protected from predators, desiccation or disturbance by a thick shell or skin. Only few, however – leaches, midge larvae and butterfly larvae – are capable of building cases to artificially protect them from the environment. Unsurpassed as artistic architects of such artificial cases are tiny caddis larvae, which live amongst the rocks, vegetation and rubbish on river beds.  These unique little creatures have developed the curious ability to use these raw materials to create colourful and unusual protective outer tubes.

Lithax in an artificial case (image: Gerhard Laukötter)

Caddis larvae are the larval stages of caddis flies (Trichoptera), of which about 12,000 species are known worldwide. Larvae of almost all species are aquatic. Larvae of about half of the species construct transportable cases, protecting soft-skinned parts of the body and in which the larvae can retreat in case of danger. All species protect their defenceless pupal stage with artificial cases, which are firmly attached to the river bed.

Depending of the larval habitat size and form of caddis cases vary, resulting in a large number of unusually constructed cases: round and square tubes, cases in the form of a turtle shell or a snail shell, sand tubes punctuated by thick stones and multi-story cases with sophisticated ventilation systems! Fascinatingly, caddis larvae use very diverse materials for case construction, including: self generated silk; sand of a defined grain size or of different grain sizes; small pieces of wood cut at an exact size by the larvae’s mouthparts; and small parts of leaves, roots or of reed stalks.


Sand: Sericostoma (image: Gerhard Laukötter)

Helicopsyche (image: Gerhard Laukötter)

Sericostoma larvae bind small sand grains together in a seemingly jointless, curved tube. Similar material is used by representatives of the genera Molanna (in flat tubes) and Helicopsyche (in winded cases, amazingly similar to a snail shell).


Silk: Micrasema (image: Gerhard Laukötter)

Larvae of the genera Micrasema and Setodes are specialized weavers, with cases made of pure silk. The diameter of the tube increases when the larvae growths.

Wood and vegetation

Crunoecia (image: Gerhard Laukötter)

Some caddis larvae species (e.g. Crunoecia which inhabits springs), cut wood fragments to a standardized size with which perfectly squared cases are built. Other species don’t care for geometry at all and assemble chaotic cases using all available wood and leaf material without any real construction plan. The important outcome – protecting the larvae – is nevertheless achieved.

Unusual and artificial material

When these preferred materials are not available, most species resourcefully change to building cases out of other more unusual material, with a range of strange and curious results.

Micropterna (case of artificial material, image: Maren Hering)

In springs with low current flow, coarse sand and gravel is often absent; and the riverbed is covered by fine sand. Species usually preferring coarse particles have to change to completely different items: using seeds, small mussel and snail shells, regardless of whether they are empty or still inhabited! On rare occasions, a fascinating form of kleptomania can be observed. Here, the cases of small larvae are used by larger larvae for building their own cases. As with snails, this is done regardless whether or not the cases are still inhabited.

Artificial material is also used by caddis larvae, and sometimes even preferred. Small fragments of red bricks or cement, fibrous tissue, even small pieces of paper or plastic have been observed as parts of colourful caddis cases.

Limnephilidae (case of Bythinella shells, image: Gerhard Laukötter)

As caddis larvae are generalists in selecting building material, several scientists have exposed larvae in laboratories. In some cases there was a scientific rationale for this. For example, larvae can be marked to observe their migration, as colourful cases are more easily found in a stream. Caddis larvae reared on a bed of small glass pieces may build a transparent case – which proves useful for scientists hoping to observe the behaviour of the larvae inside.

Limnephilus (case made of snails, image: Gerhard Laukötter)

Some biologists have offered fragments of corals, nacre, opal, malachite, lapis lazuli, garnet, rock crystal or turquoise to caddis larvae. These materials result in precious and colourful cases.

Some specimens alternately reared on two different materials some species build ringed cases.

Beautiful, natural art made by insects in seemingly everyday landscapes.  There’s often a lot more to the curious world of freshwater ecosystems than first meets the eye…

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Small red-eyed damselfly – Erythromma viridulum

Small red-eyed damselfly (image: wikipedia)

Often overlooked ultramarine marvel on a migration north

Whilst the original Cabinets of Curiosity prized (and often mythologised and fabricated) objects sourced from far-flung, exotic locations, this tiny curiosity shows you can find amazing creatures in your back garden, if only you look hard enough.  Common to weed-strewn lakes in southern Europe, the small red-eyed damselfly is tracking a warming climate north, and is the first dragonfly to have colonised Britain since records began.

In summer months throughout central Europe, you are likely to see the iridescent blue flash of the dragonfly flitting through reedbeds and bankside vegetation.  If you are lucky, you may witness the dragonfly’s peculiar mating ritual, where the male and female embrace in a heart-shape.

Male (left) and female (right) damselflies in a heart-shaped embrace (image: Ann Brooks, with permission)

Easily confused with its larger relative the Red-eyed damselfly, the small red-eyed damselfly is coloured shimmering sky-blue, with crimson red eyes.  The small red-eyed dragonfly can be distinguished by the way it holds its abdomen in an upcurve.

Find out more:

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Diving bell spider – Argyroneta aquatica

Water spider (image: wikipedia)

Submerged spiders spin silken scuba tanks

Common in northern and central Europe, the diving bell spider is the only spider that spends its whole life underwater, made possible by an amazing adaptation – the ability to spin a silken scuba tank!

The small (8-15mm) brown arachnids spin silken bubbles or “air bells” which supply oxygen, protect eggs and spiderlings, and provide a place to consume prey.  The spiders are covered with tiny hairs, which trap bubbles of air when they swim to the water surface.  The air bubbles are then transferred to the spider’s gossamer aqualung.  In fact, the spider’s Latin name Argyroneta means “silvery net”!

The silken diving bell is cunningly designed.  Its walls allow oxygen to diffuse into the air bubble and carbon dioxide to diffuse out, meaning the spider doesn’t need to regularly replenish it at the water’s surface.

An excellent swimmer, the spider will wait for prey to pass before seizing it between venomous jaws and retreating to its silk shelter.  Whilst it feeds largely on small aquatic insects, its venomous fangs are large enough to piece human skin – leading to a painful itch!

Unusually for a spider, males are considerably larger than females.   When mating, the male will (rather presumptuously) build a silk diving bell which connects to that of his intended female.  After up to 70 eggs have been laid, the diving bell provides a safe nursery, sheltered from predators until the spiderlings are large enough to disperse.

Water spider (image: wikipedia)

Where to see?

The diving bell spider is common to ponds and lakes across north and central Europe.  If you do go out pond dipping, please be careful of its painful bite!

More information:

Videos at ARKive:

ARKive video - Water spiders interactingARKive video - Water spider moving around habitat - showing diving bell

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