Do you want to slap a mosquito to death? Dinosaurs may have thought so too

Mosquitoes have a way of ruining our mood every summer night with their distinctive buzz, but we humans aren't the only ones who hate them.

Imagine that more than 100 million years ago, when the huge dinosaurs were resting in the humid jungle, the ancestors of these tiny flying creatures might have been circling them, using the same buzzing sounds and sharp mouthparts to look for opportunities to make the dinosaurs equally disgusted - yes, this blood-sucking creature appeared on the earth much earlier than us humans.

So, when did the oldest mosquito appear?

Reconstruction of the intermediate Lebanese mosquito buzzing around a dinosaur. (Photo credit: Nanjing Institute of Geology and Palaeontology)

Ancient blood sucker

Although there are more than 3,500 species of mosquitoes today, the early evolutionary history of mosquitoes has always been vague due to their tiny and fragile individuals and the difficulty of fossil preservation.

The broad mosquito family includes the Culicidae family and its sibling families Dixidae, Corethrellidae, and Chaoboridae. Molecular biology suggests that it originated in the Triassic period (about 250 million to 201 million years ago), when its sibling families had already parted ways with the Culicidae family. The two subfamilies of the modern Crown Group of Culicidae, Culicinae and Anophelinae, are speculated to have appeared in the Jurassic period.

However, no fossils of the Culicidae family were found in the Jurassic period, which is actually not in line with common sense.

Previously, the compression fossils (fossils that are compressed and flattened in sediments, with fewer details and poorer preservation than the vivid three-dimensional fossils preserved in amber) found during this period were often described as Culicidae, but considering that the integrity and clarity of their fossils cannot be compared with amber fossils, it is difficult to identify and classify these "Centilidae" fossils. They may actually belong to the Culicidae family. The earliest record of the appearance of Culicidae fossils that are more certain is in the middle Cretaceous period 100 million years ago, when scientists discovered them in Burmese amber.

Genealogy of the vampire family (Image credit: Danny Azar)

Dances with Dragons

The most attractive thing about paleontology is that there are always surprises.

Danny Aza, a Lebanese researcher from the Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, found two of the oldest male mosquito fossils in Lebanese amber, the intermediate Lebanese mosquito (Libanoculex intermedius), and classified them into a new subfamily. They lived in the early Cretaceous period 130 million years ago. This discovery pushed the fossil record of the Culicidae family back 30 million years.

Two male mosquitoes from Lebanon found in amber dating back 130 million years ago (Photo credit: Nanjing Institute of Paleontology)

What is surprising is that these two male mosquitoes actually showed obvious blood-sucking characteristics! They are surprising because this discovery is completely opposite to the habits of modern mosquitoes. Modern blood-sucking mosquitoes are all female mosquitoes, and they need to supplement sufficient energy substances and proteins from the blood of animals in order to reproduce. Modern male mosquitoes are all "vegetarians" and feed on plant nectar and the juice in fruits, stems, and leaves.

Male mosquitoes sucking plant sap (Image source: Wikipedia)

How do scientists know that these mosquitoes living in the distant Cretaceous period are blood-sucking mosquitoes? This is because the blood-sucking behavior of insects often requires a mouthpart that can penetrate the skin of animals, which is likely to have originated from the "piercing and sucking" long mouthparts of their ancestors that sucked plant sap.

In this study, scientists used advanced scientific instruments such as laser confocal microscope and fluorescence microscope from Nanjing Institute of Geology and Paleontology to carefully observe and found that the male mosquitoes in the two pieces of amber had preserved their unique blood-sucking mouthparts, including sharp triangular mandibles and elongated structures with small teeth. This means that this male mosquito was also a vampire in that era.

A Mesozoic long-mouthed insect fossil, with a very long mouthpart framed, scale: 5 mm (Image source: Conrad C. Labandeira)

Reconstruction of the long-mouthed insect Anyu scorpionfly helping gymnosperms pollinate (Photo credit: Yang Dinghua)

Detail of the mouthparts of a male mosquito in amber, scale: 10μm (Photo credit: Nanjing Institute of Geology and Paleontology)

The sharp triangular jaw and the elongated structure with small teeth, scale: 50μm (Image source: Nanjing Institute of Geology and Paleontology)

Mosquitoes have a wide range of blood-sucking targets. In addition to mammals, they also suck blood from reptiles, amphibians, and even fish and invertebrates. So it is hard to imagine that mosquitoes would stay away from dinosaurs when they dominated the earth. Therefore, it is reasonable to imagine that at least 130 million years ago, annoying mosquitoes had already swarmed around the huge dinosaurs, waiting for an opportunity to suck blood at any time.

There is more to be explained about mosquitoes...

The earliest mosquito-bearing Lebanese amber was found in Lebanon and southwestern Syria. Although Lebanese amber has a low density, is relatively fragile, easily damaged, and is not suitable for gem mining, it can be traced back to the Barremian period of the early Cretaceous period, about 130 million to 125 million years ago, and because it may have formed in tropical or subtropical temperate or hot climates, it is one of the oldest sources of amber with a large number of inclusions, and naturally has become a huge treasure trove for paleontological research.

The earliest family of flat-headed mud wasps was also found in these ambers. The two amber fossils of mosquitoes are also the result of Danny Azar's collection of nearly 500 amber sources, further proving the research potential of Lebanese amber.

Danny Azar collects amber in the wild in Lebanon (Image source: author)

This study has once again updated our understanding of the evolutionary history of mosquitoes. It not only pushed the appearance time of the original Culicidae back 30 million years, but its unique mouthpart structure also proved that male mosquitoes at that time also fed on blood. But how did all modern male mosquitoes degenerate into "vegetarians"?

Some scientists believe that an external reason is that angiosperms began to flourish in the Cretaceous period, and the "vegetarian environment" became larger.

From the perspective of benefits, first of all, blood-sucking by mosquitoes is not a win-win business for the host being sucked. It is difficult to guarantee that the host will not kill them in various ways during the blood-sucking process. If they are not careful, it will be a "mosquito tragedy" where both husband and wife die. Secondly, blood-sucking is not a rigid demand for male mosquitoes, and female mosquitoes have to take risks when reproducing the next generation. Since "vegetarianism" can provide more eating space and lower eating difficulty, and can also prevent being "killed in one pot", it is understandable that male mosquitoes choose "vegetarianism". Of course, this is just a speculation of scientists, and the specific evolutionary process still needs more fossil evidence for further research.

In short, mosquitoes are not only a part of human history, but also an ancient role in the history of the earth's biology. Their existence not only witnesses the miracle of evolution, but is also part of the diversity of nature.

References:

[1] Dany Azar, Andre Nel, Diying Huang, Michael S. Engel, The earliest fossil mosquito, Current Biology (2023), https://doi.org/10.1016/j.cub.2023.10.047.

[2] Soghigian, J., Sither, C., Justi, SA et al. Phylogenomics reveals the history of host use in mosquitoes. Nat Commun 14, 6252 (2023). https://doi.org/10.1038/s41467-023-41764-y.

Author: Wang Guanqun, Liu Yun, Danny Azar, Huang Diying

Author unit: Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences

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