A grasp of the past

by Ricardo Perez-De-La Fuente, research fellow

Few creatures look weirder – or are cooler, in my opinion – than mantidflies. There are around 400 species of these small predatory insects known worldwide – a scarce diversity by insect standards.

Like praying mantises, mantidflies have long ‘necks’ and forelegs armed with powerful spines and other structures used to hunt their prey with a sudden lethal grasp. The unfortunate victims become immobilised until they are meticulously eaten alive – not the best way to spend your last minutes on Earth!

Mantidflies belong to the Neuroptera order of insects and so aren’t actually related to praying mantises, but to insects such as lacewings and antlions.

A new paper that a colleague and I have published presents a new fossil mantidfly from Spanish amber that is important in understanding the evolution of their gripping – or raptorial – forelegs. The finding is presented in the open access journal Scientific Reports today.

Although the discovery has just been published, we excavated the new fossil during the scorching summer of 2010 in Teruel, northeastern Spain.

Amber excavations are very romantic – while they take place we carefully store the amber, piece by piece, into muddy plastic bags, remaining oblivious of what creatures are being unearthed because the amber surfaces have become opaque during fossilisation. Later, in the laboratory, the surfaces of the amber pieces are polished and screened for inclusions. Then a first glimpse is gained into what has remained frozen in time for millions of years.

It is only when the amber inclusions are carefully examined and studied that the implications of the specimens that were dug up years earlier start to be revealed. In this case, a specimen that was preserved in fragments, nothing spectacular at first look, ended up being truly exceptional.

Foreleg of Aragomantispa lacerata, showing powerful spines and other structures adapted to strike and hold prey.

Extinct true mantidflies, particularly those preserved in amber, are extremely rare. Our new fossil, pictured above at the top of the article, is 105 million years old, from the Cretaceous period. It currently stands as the oldest true mantidfly known in amber. The new extinct species, named Aragomantispa lacerata, has allowed us to compare the structures of the raptorial forelegs between extinct and extant mantidflies with an unprecedented detail.

Comparison between the foreleg spine-like structures of the new fossil mantidfly (up), with those from a close modern species (bottom).

Present-day mantidflies have forelegs with spines that bear minute cones at their tip. These cones are sensory organs that elicit the striking reflex and feel the prey’s movements once captured and restrained by the mantidfly’s tight embrace.

The forelegs of Aragomantispa lack these cones at the spines’ tip, instead having larger, icicle-shaped tips. We do not know how sensitive the mantidfly forelegs were in the Cretaceous, but the spines of at least some of these insects seem to be not as specialised as those from their present-day relatives.

Some mantidflies have smaller, reclined hair-like structures forming an edge on the leg’s surface opposing the spines. These reinforced edges create a scissor effect that stuns prey when the forelegs strike. Although Aragomatispa has these structures on the forelegs, they are also different in shape to those found on extant mantidflies.

Reconstruction of Aragomantispa lacerata striking at a hypothetical prey on a fern in the Cretaceous Spanish forest.

The fossil record offers the only direct means to assess when and how the traits characteristic of a given animal group originated in time. However, this kind of fossil evidence appears very occasionally. Our discovery shows that the foreleg spine-like structures of recent mantidflies were not fully developed in at least some of their Cretaceous ancestors.

The most exciting part is to think that this story and literally thousands more lie waiting to be discovered – or otherwise forgotten forever – buried underground.

Bursting into life

By Ricardo Pérez-de la Fuente, Museum Research Fellow

One of the earliest and toughest trials that all organisms face is birth. In egg-laying animals, the egg shell that has protected the embryo during its early development ultimately becomes a hard barrier between the animal and its life out in the world. The bursting of the egg is literally a threshold moment, and there are many ways to crack an egg…

Some animals break the egg membranes using dissolving chemicals; others physically, mechanically tear their way through the shells. Among the latter, a great diversity of animals use specialised devices called egg bursters. These vary greatly among the many arthropods and vertebrates that use them, but perhaps the most famous example is the ‘egg tooth’ that is present on the beak of newborn chicks.

Four complete Tragychrysa ovoruptora newborns preserved together with egg shell remains and one egg burster. Modified from the open access Palaeontology paper.

My colleagues and I have found an exceptional fossil in 130 million-year-old Lebanese amber. Inside, trapped together are newborn larvae from Green Lacewings, the split egg shells from where they hatched, and the minute egg bursters that the hatchlings used to crack the egg. This is a first: no definitive evidence of these specialised egg-bursting structures had been reported from the fossil record of any egg-laying animals, until now.

The finding has been recently published as open access in the journal Palaeontology. Because multiple newborns were ensnared and entombed in the resin simultaneously, the fossil larvae have been described as the new species Tragichrysa ovoruptora, meaning ‘tragic green lacewing’ and ‘egg breaking’. A sad event, indeed, taking place in an ordinary day 130 million years ago in the Cretaceous forests of Lebanon, yet a happy circumstance now that we can take a privileged glimpse into the adaptations and behaviours of these fascinating tiny creatures.

The hatchlings from modern Green Lacewings open a slit on the egg with a ‘mask’ bearing a saw-like blade. Once used, this ‘mask’ is shed together with the embryonic cuticle and is left attached to the empty egg shell.

With the help of Amoret Spooner, Collections Manager at the Museum, egg clutches from modern green lacewings were found in the Museum collections. These eggs happened to have the intact egg bursters still attached to them, and proved to be crucial to understand that we had the same structures preserved in the amber together with the newborn larvae.

Two Tragychrysa ovoruptora newborns preserved together with egg shell remains and two visible egg bursters (right inset). Modified from the open access Palaeontology paper.

Green Lacewing larvae are small predators that often carry debris as camouflage, using their sickle-shaped jaws to pierce and suck the fluids of their prey. Whereas the larvae trapped in amber differ significantly from modern-day relatives, in that they possess long tubes instead of clubs or bumps for holding debris, the studied egg shells and egg bursters are remarkably similar to those of today’s green lacewings.

The larvae were almost certainly trapped by resin while clutching the eggs from which they had freshly emerged. Such behaviour is common among modern relatives while their body hardens and their predatory jaws become functional. Indeed, the two mouthparts forming the jaws are not assembled in most of the fossil larvae, which indicates, together with the large relative size of the head and legs, that they were recently born.

Detail of a head with the jaws still dislodged, indicating that the larva was recently hatched when it was ensnared by amber and the jaws had not yet had time to fully assemble.

It may seem reasonable to assume that traits controlling a life event as decisive as hatching would have remained largely unchanged during evolution. In fact, we see in very closely related insect groups different means of hatching that can entail the loss of the egg bursters. So the persistence of a hatching mechanism in a given animal lineage through deep time can’t be determined without direct proof from the fossil record.

Reconstruction of two Tragichrysa ovoruptora newborns clutching the eggs from where they recently hatched, moments before they were trapped by resin. Larvae colour and egg stalks are conjectural. Extracted from the open access Palaeontology paper.

This new discovery shows that the mechanism green lacewings use to crack the egg was already established 130 million years ago. Overall, it represents the first direct evidence of how insects hatched in deep time, egg-bursting their way through into life.

*

The hatching mechanism of 130-million-year-old insects: an association of neonates, egg shells and egg bursters in Lebanese amber by Ricardo Pérez-de la Fuente, Michael S. Engel, Dany Azar and Enrique Peñalver is published as open access in Palaeontology this month.

Bee beautiful

Our conservator Bethany Palumbo tells us how she restored a beautiful 19th-century papier-mâché model of a honeybee hive, created by master model-maker and anatomist Louis Thomas Jérôme Auzoux

Louis Thomas Jérôme Auzoux

Although the Museum’s collections are mostly of organic specimens, we also hold a fascinating collection of scientific models made to represent the natural world, made from all types of materials, from wax and cardboard to plaster and paint.

We are lucky enough to own a model made by esteemed French anatomist Louis Auzoux (1797-1880), who in the late 19th century developed a method of building strong yet light papier-mâché models that could be taken apart and rebuilt, allowing internal elements such as tissues and organs to be studied in detail.

Model of a honeybee hive in box with six bees, by Louis Auzoux

While Auzoux made many models demonstrating human anatomy, he later expanded his business to include magnified models of plants and insects. The model we have is of a honeybee hive, containing six beautiful bees.

The hive, painted with a protein-based paint and varnished with gelatine, is large enough to allow the viewer to see the fine details of the hive, including individual chambers containing tiny larvae.

As you can see in the image at the top of the article, the bees themselves are also intricately painted, with rabbit hair used to simulate their natural fuzz, and delicate wings constructed from metal wire.

While there was much to admire about this model, it was in received in poor condition. Previous restoration attempts had introduced many materials that were now failing. There were fills, constructed of paper, applied to areas in an attempt to hide cracks in the original model. These were covered in oil paint, which was dripping over the original paintwork and had become brittle and discoloured.

Oil paint layers were peeling from the model

The whole hive was coated in a layer of cellulose nitrate film, a popular coating in the mid-20th century which was used as protection and to create a gloss finish. This coating doesn’t age well, resulting in peeling. It had also been applied to the bees themselves, clumping together the bee ‘fuzz’ and disguising the paintwork underneath.

The priority for treatment was to return the model to its original form while stabilising it for the future.

I undertook treatment in several stages over the course of six months. First, the cellulose nitrate film was removed from all areas using acetone, which could be applied with a cotton bud and fortunately didn’t affect the paint layer beneath.

Fill material used to cover previous damage had become discoloured

The next stage was to remove the discoloured oil paint from the hive. This was done manually using metal and wooden tools lubricated with white spirit, which were used to gently scrape the surface under magnification. This revealed old fills on the hive, made from a combination of plastic tape, paper and old adhesives which also needed to be removed. They were easily softened with water and gently peeled away.

Once all unstable introduced materials were removed, work began to stabilise the original model. The bees were suffering from paint cracking and peeling, as seen in the magnified photograph below.

Peeling paint at 6x magnification

We decided to consolidate this using gelatine as it would be in keeping with the original construction and could easily be reversed if necessary. Gelatine was mixed in water and warmed to make it a thin consistency, and then applied with a paintbrush. Once the paint flakes had softened they could be gently pressed down. Gelatine was also used with acid-free tissue to stabilise the cracks and areas of surface loss on the hive.

With the hive and bees now clean and stable, the quality of this piece and its incredible paintwork can really be admired. We hope to put it on display soon for all our visitors to enjoy!

Marvellous Mantodea

In the latest display in our Presenting… series, collections manager Amoret Spooner takes a look at the wonderful and sometimes strange world of the praying mantis.

Praying mantis is the common name given to an order of insects called Mantodea, a word which derives from mantis meaning prophet, and eidos meaning form or type. The more familiar ‘praying mantis’ refers to the striking way that they hold their large forelimbs, in a ‘praying’ posture.

Display of different mantis species

There are over 2,400 species of mantis worldwide, split into 21 different families. The image above shows their incredible diversity of colour, shape and size. But while they may differ in appearance, their biology and many behavioural traits are the same.

Mantis are predators of insects, including other mantis, but larger species will eat small lizards and birds. But they are perhaps best known for being cannibalistic. This behaviour is most commonly seen in nymphs straight out of the egg case, or ootheca, but it can also occur when the female eats the male after mating. However, cannibalism is not required to mate, so when it happens it’s usually because the female is hungry!

The egg case, or ootheca, of mantis vary greatly depending on the size and behaviour of the species.
Revisio Insectorum Familiae Mantidarum was one of John Obadiah Westwood’s greatest works. Thankfully he kept all of his drawings, annotated pages and notes for the publication, allowing us an insight into the years of work he put into its production.

Praying mantis are ambush hunters, either camouflaging themselves while waiting for their prey to approach, or actively stalking prey. Their compound eyes are specialised in perceiving motion, and are widely spaced giving them a wide field of vision. Along with powerful front legs and an ability to move the head up to 180°, this makes them successful predators.

The Museum’s archive contains original drawings and annotations by John Obadiah Westwood (1805–1893), the first Hope Professor of Zoology. As a renowned scientist Westwood described many new mantis species, and he was also a talented artist.

The Presenting… Marvellous Mantodea case is on display at the Museum until 1 November 2018.

Cicada serenade

A Spotlight Specimens special for Oxford Festival of Nature

by Leonidas-Romanos Davranoglou, DPhil student, Animal Flight Group, Department of Zoology, University of Oxford

Anyone walking on a summer day in hot places such as the Mediterranean or the tropics will have heard cicadas singing. Cicadas actually are among the loudest of all animals, singing at up to 120 dB – as loud as a passing freight train. In fact, you can damage your ear if a particularly loud species starts singing next to your head.

Some countries even have health and safety policies which prevent people from working outdoors when cicadas are singing. If a single cicada can sing that loud, you can imagine what a forest filled with them sounds like!

Tropical cicadas from the Museums' collections
Tropical cicadas from the Museums’ collections

Only male cicadas sing, primarily to attract females, much like a Romeo singing to his Juliet. Females are mute, but they respond to males of their liking by flicking their wings, generating a loud click. Entomologists often mimic the female response by snapping their fingers under a tree containing cicadas. In this way, they can collect males eager to mate, which would otherwise be too high in the tree to reach.

An unpleasant parasitic fungus capitalises on this arrangement: The fungus basically consumes the innards of the male cicadas, causing their private parts to fall off – in effect castrating them. A castrated male may stop singing and as a result, other males try to mate with it, and in this way the fungus is transmitted from male to male.

But how do these famous (or notorious, if you find them annoying) cicadas produce these incredible sounds? This has remained a mystery since the time of the ancient Greeks, who admired these animals. But the matter was settled through a collaboration between Oxford University and Australian scientists. The physical process is not too complex and you can get a good idea how it works by using an empty plastic bottle.

Cicadas have a unique membrane on the sides of their abdomen called the tymbal membrane, which is strong but flexible. Internally, two huge muscles attach to this membrane. When the muscles contract, they pull and buckle the membrane inwards to produce a strong popping sound. You can imitate this by squeezing an empty plastic bottle in and out. Speed up this process by a few hundred buckles per second and you get a cicada’s song.

PowerPoint Presentation
Dorsal view of the abdomen of the cicada Cicadetta flaveola, showing the two membranes on the sides of the abdomen (tymbal membrane).
Lateral view of a dissected cicada, Tibicen plebejus. The huge muscle attaches to the tymbal memembrane, and pulls it inwards to generate a loud click. Note that after the large muscle, the abdomen is largely hollow.
Lateral view of a dissected cicada, Lyristes plebejus. The huge muscle attaches to the tymbal memembrane, and pulls it inwards to generate a loud click. After the large muscle, the abdomen is largely hollow.

Producing sound however, is not enough. Just like we have to talk with a particular loudness so people can hear us, cicadas must find ways of amplifying their sound, so females can hear them from very far away. The way cicadas achieve this is via something called Helmholtz resonance. You can create this phenomenon by blowing air across the top of the empty bottle you just used to create the pop.

Blowing across a bottle produces sound due to the behaviour of air when it is confined in a container with an open hole. The abdomen of cicadas forms a Helmholtz resonator as well: it is completely hollow, and two openings on the underside, called tympana, act as the top of a bottle and radiate sound in the same way.

Ventral view of a dissected cicada, Tibicen plebejus. The large aperture is the tympanum, which acts as the amplifier for the cicadas' song. The hole of an empty bottle behaves in the same way when you blow air over it.
Ventral (underside) view of a dissected cicada, Lyristes plebejus. The large opening is the tympanum, which acts as the amplifier for the cicada’s song. The hole of an empty bottle behaves in the same way when you blow air over it.

The singing habits and unique anatomy of the cicadas are perhaps best summarized in a quote by 19th-century entomologist Jean Henri Fabre, who, poetically as always, said:

Assuredly one must be passionately devoted to music thus to clear one’s internal organs in order to make room for a musical box!

OFoN_logo_green block_small